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Q Name a disease transmitted by direct contact medicine 223 order lopinavir with mastercard, a disease transmitted by indirect contact, and a disease transmitted by droplet transmission. Houseflies, for instance, can transfer the pathogens of typhoid fever and bacillary dysentery (shigellosis) from the feces of infected people to food. The pathogens then reproduce in the vector, and the increase in the number of pathogens increases the possibility that they will be transmitted to another host. Some parasites reproduce in the gut of the arthropod; these can be passed with feces. If the arthropod defecates or vomits while biting a potential host, the parasite can enter the wound. Some protozoan and helminthic parasites use the vector as a host for a developmental stage in their life cycle. Traditionally these were called nosocomial infections (nosocomial is Latin for hospital). Microorganisms in the Hospital Although every effort is made to kill or check the growth of microorganisms in the hospital, the hospital environment is a major reservoir for a variety of pathogens. Then, during the 1980s, antibiotic-resistant gram-positive bacteria, Staphylococcus aureus, coagulase-negative staphylococci (see page 422), and Enterococcus spp. By the 1990s, these gram-positive bacteria accounted for 34% of nosocomial infections, and four gram-negative pathogens accounted for 32%. In addition to being opportunistic, some microorganisms in the hospital become resistant to antimicrobial drugs, which are commonly used there. Most of these pneumonias are related to respiratory devices that aid breathing or administer medications. Intravenous catheterization is implicated in haIs of the bloodstream, particularly infections caused by bacteria and fungi. Burns, surgical wounds, trauma (such as accidental wounds), injections, invasive diagnostic procedures, ventilators, intravenous therapy, and urinary catheters (used to drain urine) can all break the first line of defense and make a person more susceptible to disease in hospitals. Burn patients are especially susceptible to nosocomial infections because their skin is no longer an effective barrier to microorganisms. The risk of infection is also related to other invasive procedures, such as administering anesthesia, which may alter breathing and contribute to pneumonia, and tracheotomy, in which an incision is made into the trachea to assist breathing. Patients who require invasive procedures usually have a serious underlying disease, which further increases susceptibility to infections. Invasive devices provide a pathway for microorganisms in the environment to enter the body; they also help transfer microbes from one part of the body to another. In healthy individuals, white blood cells called T cells (T lymphocytes) provide resistance to disease by killing pathogens directly, mobilizing phagocytes and other lymphocytes, and secreting chemicals that kill pathogens. White blood cells called B cells (B lymphocytes), which develop into antibodyproducing cells, also protect against infection. Antibodies provide immunity by such actions as neutralizing toxins, inhibiting the attachment of a pathogen to host cells, and helping to lyse pathogens. Drugs, radiation therapy, steroid therapy, burns, diabetes, leukemia, kidney disease, stress, and malnutrition can all adversely affect the actions of T and B cells and compromise the host. These strains become part of the microbiota of patients and hospital personnel and become progressively more resistant to antibiotic therapy. In this way, people become part of the reservoir (and chain of transmission) for antibioticresistant strains of bacteria. Chain of transmission Given the variety of pathogens (and potential pathogens) in health care settings and the compromised state of the host, routes of transmission are a constant concern. Because health care personnel are in direct contact with patients, they can often transmit disease. For example, a physician or nurse may transmit microbes to a patient when changing a dressing, or a kitchen worker who carries Salmonella can contaminate a food supply. Certain areas of health care facilities are reserved for specialized care; these include the burn, hemodialysis, recovery, intensive care, and oncology units. Unfortunately, these units Compromised Host A compromised host is one whose resistance to infection is impaired by disease, therapy, or burns. Two principal conditions can compromise the host: broken skin or mucous membranes, and a suppressed immune system. ChaPter 14 Principles of Disease and epidemiology 405 also group patients together and provide environments for the epidemic spread of nosocomial infections from patient to patient. Many diagnostic and therapeutic hospital procedures provide a fomite route of transmission. Needles may introduce pathogens into muscle or blood, and surgical dressings can become contaminated and promote disease (see page 411). Infection can range from asymptomatic colonization of patients to diarrhea or colitis. On average, health care workers wash their hands before interacting with patients only 40% of the time. Respirators and humidifiers provide both a suitable growth environment for some bacteria and a method of airborne transmission. Most hospitals have at least an infection control nurse or epidemiologist (an individual who studies disease in populations). The role of these staff members is to identify problem sources, such as antibiotic-resistant strains of bacteria and improper sterilization techniques. The infection control officer should make periodic examinations of hospital equipment to determine the extent of microbial contamination. Samples should be taken from tubing, catheters, respirator reservoirs, 390 403 405 407 412 and other equipment. An emerging disease can be caused by a virus, a bacterium, a fungus, a protozoan, or a helminth. About 75% of emerging infectious diseases are zoonotic, mainly of viral origin, and are likely to be vector-borne. For example, influences the evolution of microorganisms some diseases present symp. Some are recognized because improved diagnostic techniques allow the identification of a new pathogen. Others are identified when a local disease becomes widespread, a rare disease becomes common, a mild disease becomes more severe, or an increase in life span permits a slow disease to develop. A variety of factors contribute to the emergence of new infectious diseases: New strains, such as E. A new serovar, such as Vibrio cholerae O139, may result from changes in or the evolution of existing microorganisms. The widespread, and sometimes unwarranted, use of antibiotics and pesticides encourages the growth of more resistant populations of microbes and the insects (mosquitoes and lice) and ticks that carry them. ChaPter 14 Principles of Disease and epidemiology 407 Global warming and changes in weather patterns may increase the distribution and survival of reservoirs and vectors, resulting in the introduction and dissemination of diseases such as malaria and Hantavirus pulmonary syndrome. Known diseases, such as chikungunya (or dengue) and West Nile virus, may spread to new geographic areas by modern transportation. This was less likely 100 years ago, when travel took so long that infected travelers either died or recovered during passage. Previously unrecognized infections may appear in individuals living or working in regions undergoing ecological changes brought about by natural disaster, construction, wars, and expanding human settlement. In California, the incidence of coccidioidomycosis increased tenfold following the Northridge earthquake of 1994. Workers clearing South American forests are now contracting Venezuelan hemorrhagic fever. The increase in Lyme disease in recent years could be due to rising deer populations resulting from the killing of deer predators. Failures in public health measures may be a contributing factor to the emergence of previously controlled infections. For example, the failure of adults to get a diphtheria booster vaccination led to a diphtheria epidemic in the newly independent republics of the former Soviet Union in the 1990s. To detect, promptly investigate, and monitor emerging infectious pathogens, the diseases they cause, and factors that influence their emergence 2. A contaminated food or water supply, for example, can affect many thousands of people very quickly. Identifying the causative agent of a disease is desirable so it can be effectively controlled and treated. It is also desirable to understand the mode of transmission and geographical distribution of the disease. John Snow, a British physician, conducted a series of investigations related to outbreaks of cholera in London.

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Similarly symptoms 12 dpo buy lopinavir master card, ocean estuaries (fed by rivers) have higher nutrient levels and therefore larger microbial populations than other shoreline waters. In water, particularly with low nutrient concentrations, microorganisms tend to grow on stationary surfaces and on particulate matter. In this way, a microorganism has contact with more nutrients than if it were randomly suspended and floating freely with the current. Many bacteria whose main habitat is water often have appendages and holdfasts that attach to various surfaces. Freshwater Microbiota A typical lake or pond serves as an example of the various zones and the kinds of microbiota found in a body of fresh water. The littoral zone along the shore has considerable rooted vegetation, and light penetrates throughout it. The limnetic zone consists of the surface of the open water area away from the shore. Microbial populations of freshwater bodies tend to be affected mainly by the availability of oxygen and light. In many ways, light is the more important resource because photosynthetic algae are the main source of organic matter, and hence of energy, for the lake. These organisms are the primary producers of a lake that support a population of bacteria, protozoa, fish, and other aquatic life. Microorganisms growing on nutrients in stagnant water quickly use up the dissolved oxygen in the water. Wave action in shallow layers, or water movement in rivers, tends to increase the amount of oxygen throughout the water and aid in the growth of aerobic populations of bacteria. Movement thus improves the quality of water and aids in the degradation of polluting nutrients. Deeper waters of the profundal and benthic zones have low oxygen concentrations and less light. These bacteria are anaerobic photosynthetic organisms that metabolize H2S to sulfur and sulfate in the bottom sediments of the benthic zone. Clostridium species are common in bottom sediments and may include botulism organisms, particularly those causing outbreaks of botulism in waterfowl. These organisms are mostly Archaea, which adapt well to environmental stresses and have low energy requirements. One conclusion, so far, has been that nearly a third of all life on the planet consists of microbes that live, not in ocean waters, but under the seafloor. These microbes make immense amounts of methane gas that could be environmentally damaging if it were to be released into the atmosphere. Populations of different strains vary at different depths according to their adaptations to available sunlight. A drop of seawater might contain 20,000 cells of Prochlorococcus, a tiny sphere less than 0. This unseen population of microscopic organisms fills the upper 100 meters of ocean and exerts a profound influence on life on Earth. The support of oceanic life depends largely on ChaPter 27 Environmental Microbiology 781 Luminous organ the role of Microorganisms in Water Quality Water in nature is seldom totally pure. Water Pollution the form of water pollution that is our primary interest is microbial pollution, especially by pathogenic organisms. The most dangerous form of water pollution occurs when feces enter the water supply. Globally, it is estimated that waterborne diseases are responsible for over 2 million deaths each year, mostly among children under the age of 5. Examples of such diseases are typhoid fever and cholera, caused by bacteria that are shed only in human feces. Improvements in sanitation, including the use of sand filter beds, in developed nations have greatly reduced incidence. Chemical Pollution Preventing chemical contamination of water is a difficult problem. Industrial and agricultural chemicals leached from the land enter water in great amounts and in forms that are resistant to biodegradation. Rural waters often have excessive amounts of nitrate from agricultural fertilizers. When ingested, the nitrate is converted to nitrite by bacteria in the gastrointestinal tract. Nitrite competes for oxygen in the blood and is especially likely to harm infants. Billions of these in every liter of seawater double in number every few days and are consumed at about the same rate by microscopic predators. Immense populations of another bacterium, Pelagibacter ubique, metabolize the waste products of these photosynthetic populations (see the discussion under Microbial Diversity in Chapter 11 on page 315). In waters below about 100 meters, members of the Archaea begin to dominate microbial life. Planktonic members of this group of the genus Crenarchaeota (kren-ar-K-tah) account for much of the microbial biomass of the oceans. These organisms are well adapted to the cool temperatures and low oxygen levels of oceanic depths. Microbial bioluminescence, or light emission, is an interesting aspect of deep-sea life. Many bacteria are luminescent, and some have established symbiotic relationships with benthicdwelling fish. She tells him that she had been to China, the Philippines, haiti, Chile, and indonesia. Just before leaving haiti to go home, Charity had eaten fried shrimp and prawns purchased from a local market and prepared by a local family. She also recalled drinking a half glass of water with her dinner; she did not know whether it was bottled water. Purple and green sulfur bacteria are photosynthetic organisms, but they are generally found deep in freshwater rather than at the surface. As a result, phosphate-containing detergents and lawn fertilizers are banned in many places. Water Purity tests Historically, most of our concern about water purity has been related to the transmission of disease. Therefore, tests have been developed to determine the safety of water; many of these tests are also applicable to foods. For one thing, if we were to find the pathogens causing typhoid or cholera in the water system, the discovery would already be too late to prevent an outbreak of the disease. Moreover, such pathogens would probably be present only in small numbers and might not be included in tested samples. The tests for water purity in use today are aimed instead at detecting particular indicator organisms. The most important criterion is that the microbe be consistently present in human feces in substantial numbers so that its detection is a good indication that human wastes are entering the water. The indicator organisms should also survive in the water at least as well as the pathogens would. The indicator organisms must be detectable by simple tests that can be carried out by people with relatively little training in microbiology. In the United States, the usual indicator organisms in freshwater are the coliform bacteria. Because some coliforms are not solely enteric bacteria but are more commonly found in plant and soil samples, many standards for food and water specify the identification of fecal coliforms. There are specialized tests to distinguish fecal coliforms from nonfecal coliforms. Note that coliforms are not themselves pathogenic under normal conditions, although certain strains can cause diarrhea (see Chapter 25, page 719) and opportunistic urinary tract infections (see Chapter 26, page 749). The methods for determining the presence of coliforms in water are based largely on the lactose-fermenting ability of coliform bacteria.

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Animals infected with the spirochete shed the bacteria in their urine for extended periods medications rights generic lopinavir 250mg with amex. In rats, the bacteria inhabit renal tubules, an immunologically privileged site, where they continue to reproduce and are shed, copiously, in urine for cystitis Cystitis is a common inflammation of the urinary bladder in females. The female urethra is less than 2 inches long, and microorganisms traverse it readily. These considerations are reflected in the fact that the rate of urinary tract infections in women is eight times that of men. Lactose-fermenting, gram-negative rods are cultured from her urine (see the photo). Designed to selectively grow gram-negative bacteria and differentiate them by their ability to ferment lactose. Disease cystitis (urinary bladder infection) Pyelonephritis (kidney infection) Leptospirosis (kidney infection) Pathogen Escherichia coli, Staphylococcus saprophyticus primarily E. Humans become infected by contact with urine-contaminated water from freshwater lakes or streams, soil, or sometimes with animal tissue. People whose occupations expose them to animals or animal products are most at risk. Usually the pathogen enters through minor abrasions in the skin or mucous membranes. Domestic dogs have a sizable rate of infection; even when immunized, they may continue to shed leptospira. After an incubation period of 1 to 2 weeks, headaches, muscular aches, chills, and fever abruptly appear. Several days later, the acute symptoms disappear, and the temperature returns to normal. Because of this, the immune response is delayed long enough (1 or 2 weeks) for the population in the blood and tissues to reach enormous numbers. An emerging form of leptospirosis, pulmonary hemorrhagic syndrome, has appeared globally. Affecting the lungs with massive bleeding, it has a fatality rate of more than 50%. Recovery results in a solid immunity, but only to the particular serovar involved. Chapter 26 Microbial Diseases of the Urinary and Reproductive Systems 751 Most cases of leptospirosis are diagnosed by a serological test that is complicated and usually done by central laboratories. However, a number of rapid serological tests are available for a preliminary diagnosis. Doxycyline (a tetracycline) is the recommended antibiotic for treatment; however, administration of antibiotics in later stages is often unsatisfactory. That immune reactions are responsible for pathogenesis in this stage may be an explanation. Maricel had really enjoyed the excursion because it included kayaking in streams near isolated rural villages, so she was able to get a feel for the "real" Costa Rica. Why is urethritis, an infection of the urethra, frequently preliminary to further infections of the urinary tract An ancient disease, gonorrhea was described and given its present name by the Greek physician Galen in A. To infect, the gonococcus must attach to the mucosal cells of the epithelial wall by means of fimbriae. The pathogen invades the spaces separating columnar epithelial cells, which are found in the oral-pharyngeal area, the eyes, rectum, urethra, opening of the cervix, and the external genitals of prepubertal females. The invasion sets up an inflammation and, when leukocytes move into the inflamed area, the characteristic pus forms. About 80% of infected men show these obvious symptoms after an incubation period of only a few days; most others show symptoms in less than a week. More than 30 bacterial, viral, or parasitic infections have been identified as sexually transmitted. Many of these infections can be successfully treated with antibiotics and can be largely prevented by the use of condoms. Home test kits can speed diagnosis and treatment, allowing individuals who might otherwise avoid the health clinic to privately begin the screening process. People with positive tests receive referrals to nearby clinics for counseling and treatment options. There is also an option on the website allowing the user to anonymously notify sexual partners that they may also be infected. These tests also look for presence of leukocytes, which indicate an immune response to an infection. Pros of at-home testing More Cases Diagnosed In a 5-year period, the "I Want the Kit" initiative detected more chlamydial infections than traditional clinics did in the areas where it was available. Its creators estimate that this method of testing would save about $41,000 in direct medical costs per 10,000 women, when compared with clinic-based screening. Better Access for Patients Home testing kits can also be very helpful for people with limited transportation or for residents of rural areas who live far from medical facilities. Most home test kits are available at drugstores or can be ordered online or over the phone. Quicker Treatment Providing a screening method that works for people who are reluctant or unable to visit a clinic means more diagnoses and quicker treatment. Privacy Allowing access to test information through a hotline or website raises concerns that results may fall into the hands of someone other than the patient. Not All Home Test Kits Are Equally Accurate Unfortunately, not every home test kit sold online today is necessarily effective. And regardless of test results, a person with persistent or worsening symptoms should always see a health care provider. Positive Result If there is a line next to the "T", however faint, the result is positive. Certain gram-negative organisms convert nitrates to nitrites, so the presence of nitrites in urine can indicate urinary tract infection. The vaginal walls are composed of stratified squamous epithelial cells, which are not colonized. Later in the course of the disease, there might be abdominal pain from complications such as pelvic inflammatory disease (discussed on page 757). In both men and women, untreated gonorrhea can disseminate and become a serious, systemic infection. Complications of gonorrhea can involve the joints, heart (gonorrheal endocarditis), meninges (gonorrheal meningitis), eyes, pharynx, or other parts of the body. Gonorrheal arthritis, which is caused by the growth of the gonococcus in fluids in joints, occurs in about 1% of gonorrhea cases. If a mother is infected with gonorrhea, the eyes of her infant can become infected as it passes through the birth canal. Because of the seriousness of this condition and the difficulty of being sure the mother is free of gonorrhea, antibiotics are placed in the eyes of all newborn infants. If the mother is known to be infected, an intramuscular injection of antibiotic is also administered to the infant. Gonorrheal infections can also be transferred by hand contact from infected sites to the eyes of adults. Gonorrheal infections can be acquired at any point of sexual contact; pharyngeal and anal gonorrhea are not uncommon. The symptoms of pharyngeal gonorrhea often resemble those of the usual septic sore throat. The gonococcus is very sensitive to adverse environmental influences (desiccation and temperature) and survives poorly outside the body. It even requires special transporting media to keep it viable for short intervals before the cultivation is under way. Cultivation has the advantage of allowing determination of antibiotic sensitivity.

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Thus treatment sciatica safe lopinavir 250 mg, 795 797 801 804 806 807 796 part Five environmental and Applied Microbiology 1 Blanching in hot water or steam softens the product to easily fill the can. Washing, sorting, blanching Steam box this treatment lowers the microbial population and destroys enzymes that might alter color, flavor, or texture. Many industries have standards for the numbers of such thermophilic bacteria permitted in raw materials. Both types of spoilage occur only when the cans are stored at higher than normal temperatures, which permits the growth of bacteria whose endospores are not destroyed by normal processing. Mesophilic bacteria can spoil canned foods if the food is underprocessed or if the can leaks. Leaking cans are often contaminated during the cooling of cans after processing by heat. The hot cans are sprayed with cooling water or passed through a trough filled with water. Contaminating bacteria in the cooling water are drawn into the can with the water. Spoilage from underprocessing or can leakage is likely to produce odors of putrefaction, at least in high-protein foods, and occurs at normal storage temperatures. In such types of spoilage, there is always the potential that botulinal bacteria will be present. Occasional problems in acidic foods develop from a few microorganisms that are both heat resistant and acid tolerant. Radiation is measured in Grays, named for an early radiologist-often in terms of thousands of Grays, abbreviated as kGy. Farkas, "physical Methods of Food preservation," in Food Microbiology: Fundamentals and Frontiers, 2d ed. Low doses of irradiation (less than 1 kGy) are used to kill insects (disinfestation) and inhibit sprouting, as in stored potatoes. Pasteurizing doses (1 to 10 kGy) can be used on meats and poultry to eliminate or critically reduce the numbers of specific bacterial pathogens. High doses (more than 10 kGy) are used to sterilize, or at least greatly lower, the bacterial populations in many spices. Spices are often contaminated with 1 million or more bacteria per gram, although these are not considered to be normally hazardous to health. Aseptic Packaging the use of aseptic packaging to preserve food has been increasing. Packages are usually made of some material that cannot tolerate conventional heat treatment, such as laminated paper or plastic. Metal containers can be sterilized with superheated steam or other high-temperature methods. While still in the sterile environment, the material is formed into packages, which are then filled with liquid foods that have been conventionally sterilized by heat. A specialized use of irradiation has been to sterilize meats eaten by American astronauts, and a few health facilities have selectively used irradiation to sterilize foods ingested by immunocompromised patients. Irradiated food is marked in the United States with a radura symbol and a printed notice. Unfortunately, this symbol has often been interpreted as a warning rather than the description of an approved processing treatment or preservative. Chang initiates a case-control study with representatives of the state health departments that had reported S. Fifteen items, suspected as possible vehicles of infection on the basis of the individual case investigations, are listed. State officials determine whether each suspect item was used or consumed by the infected person within the 3 days before onset of illness. Controls were asked the same questions as patients, except that they were questioned about the use or consumption of the 15 suspect items during the previous month. Foil-Wrapped Chocolate Balls ate Did not eat Cases 38 7 Controls 12 79 radiation and Industrial Food Preservation It has long been recognized that irradiation is lethal to microorganisms; in fact, a patent was issued in Great Britain in 1905 for the use of ionizing radiation to improve the condition of foodstuffs. X rays were specifically suggested in 1921 as a way to inactivate the larvae in pork that are the cause of trichinellosis. The ionizing irradiation is usually X rays or the gamma rays produced by radioactive cobalt-60. Up to certain energy levels, high-energy electrons produced by electron accelerators are also used. These sources inactivate the target organisms and do not induce radioactivity in the food or packaging material. This development quickly led to an improved understanding of the relationships between specific microbes and their products and activities. For example, once it was understood that a certain yeast grown under certain conditions produced beer and that certain bacteria could spoil the beer, brewers were better able to control the quality of their products. Specific industries became active in microbiological research and selected certain microbes for their special qualities. The brewing industry extensively investigated the isolation and identification of yeasts and selected those that could produce more alcohol. In this section, we will discuss the role of microorganisms in the production of several common foods. Cheese the United States leads the world in the making of cheese, producing millions of tons every year. Another recent application is to irradiate mail to kill possible bioterrorism agents that it might contain, such as anthrax endospores. Electron gun High-Pressure Food Preservation A recent development in food preservation has been the use of a high-pressure processing technique (pascalization). Prewrapped foods such as fruits, deli meats, and precooked chicken strips are submerged into tanks of pressurized water. The pressure can reach 87,000 pounds per square inch (psi)-which has been compared to the equivalent of about three elephants standing on a dime. This process kills many bacteria, such as Salmonella, Listeria, and pathogenic strains of E. It also kills nonpathogenic microorganisms that tend to shorten the shelf life of such products. Because the process does not require additives, it does not require regulatory approval. These machines generate an electron stream that is accelerated down a long tube by electromagnets of the opposite charge. The vertical beam is swept back and forth over the target as it is moved past the beam. The penetrating power of the beam is limited: if the target substance is expressed as an equivalent thickness of water, the maximum is about 3. These inoculated lactic acid bacteria also provide the characteristic flavors and aromas of fermented dairy products during the ripening process. The curd undergoes a microbial ripening process, except in the case of a few unripened cheeses, such as ricotta and cottage cheese. Cheeses are generally classified by their hardness, which is produced in the ripening process. The more moisture lost from the curd and the more the curd is compressed, the harder the cheese. The hard cheddar and Swiss cheeses are ripened by lactic acid bacteria growing anaerobically in the interior.

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Suppose we want to grow a culture of a certain microorganism symptoms pancreatitis buy lopinavir 250mg amex, perhaps the microbes from a particular clinical specimen. First, it must contain the right nutrients for the specific microorganism we want to grow. It should also contain sufficient moisture, a properly adjusted pH, and a suitable level of oxygen, perhaps none at all. The medium must initially be sterile-that is, it must initially contain no living microorganisms-so that the culture will contain only the microbes (and their offspring) we add to the medium. A wide variety of media are available for the growth of microorganisms in the laboratory. Media are constantly being developed or revised for use in the isolation and identification of bacteria that are of interest to researchers in such fields as food, water, and clinical microbiology. When it is desirable to grow bacteria on a solid medium, a solidifying agent such as agar is added to the medium. A complex polysaccharide derived from a marine alga, agar has long been used as a thickener in foods such as jellies and ice cream. Agar has some very important properties that make it valuable to microbiology, and no satisfactory substitute has yet been found. The test tubes are called slants when their contents are allowed to solidify with the tube held at an angle so that a large surface area for growth is available. Petri dishes, named for their inventor, are shallow dishes with a lid that nests over the bottom to prevent contamination; when filled, they are called Petri (or culture) plates. Organisms of this type, such as Lactobacillus (page 310), are sometimes used in tests that determine the concentration of a particular vitamin in a substance. To perform such a microbiological assay, a growth medium is prepared that contains all the growth requirements of the bacterium except the vitamin being assayed. Then the medium, test substance, and bacterium are combined, and the growth of bacteria is measured. This bacterial growth, which is reflected by the amount of lactic acid produced, will be proportional to the amount of vitamin in the test substance. The more lactic acid, the more the Lactobacillus cells have been able to grow, so the more vitamin is present. Most heterotrophic bacteria and fungi, such as you would work with in an introductory lab course, are routinely grown on complex media made up of nutrients including extracts from yeasts, meat, or plants, or digests of proteins from these and other sources. In complex media, the energy, carbon, nitrogen, and sulfur requirements of the growing microorganisms are provided primarily by protein. Proteins are large, relatively insoluble molecules that only a minority of microorganisms can utilize directly. Partial digestion by acids or enzymes reduces proteins to shorter chains of amino acids called peptones. Vitamins and other organic growth factors are provided by meat extracts or yeast extracts. The soluble vitamins and minerals from the meats or yeasts are dissolved in the extracting water, which is then evaporated, so these factors are concentrated. In a recently introduced system, each individual Petri plate (OxyPlate) becomes an anaerobic chamber. The medium in the plate contains an enzyme, oxyrase, which combines oxygen with hydrogen, removing oxygen as water is formed. Because anaerobes might be killed by exposure to oxygen, special media called reducing media must be used. These media contain ingredients, such as sodium thioglycolate, that chemically combine with dissolved oxygen and deplete the oxygen in the culture medium. To routinely grow and maintain pure cultures of obligate anaerobes, microbiologists use reducing media stored in ordinary, tightly capped test tubes. When water is mixed with the chemical packet containing sodium bicarbonate and sodium borohydride, hydrogen and carbon dioxide are generated. Reacting on the surface of a palladium catalyst in a screened reaction chamber, which may also be incorporated into the chemical packet, the hydrogen and atmospheric oxygen in the jar combine to form water. Also in the jar is an anaerobic indicator containing methylene blue, which is blue when oxidized and turns colorless when the oxygen is removed (as shown here). Materials are introduced through the small doors in the air-lock chamber at the left. Q In what way would an anaerobic chamber resemble the Space Laboratory orbiting in the vacuum of space Mycobacterium leprae, the leprosy bacillus, is now usually grown in armadillos, which have a relatively low body temperature that matches the requirements of the microbe. Another example is the syphilis spirochete, although certain nonpathogenic strains of this microbe have been grown on laboratory media. With few exceptions, the obligate intracellular bacteria, such as the rickettsias and the chlamydias, do not grow on artificial media. Cultures are placed in a large sealed jar containing a lighted candle, which consumes oxygen. The candle stops burning when the air in the jar has a lowered concentration of oxygen (at about 17% O2, still adequate for the growth of aerobic bacteria). Candle jars are still used occasionally, but more often commercially available chemical packets are used to generate carbon dioxide atmospheres in containers. When only one or two Petri plates of cultures are to be incubated, clinical laboratory investigators often use small plastic bags with self-contained chemical gas generators that are activated by crushing the packet or moistening it with a few milliliters of water. These packets are sometimes specially designed to provide precise concentrations of carbon dioxide (usually higher than can be obtained in candle jars) and oxygen for culturing organisms such as the microaerophilic Campylobacter bacteria (page 302). The lab is a sealed environment within a larger building and has an atmosphere under negative pressure, so that aerosols containing pathogens will not escape. The laboratory itself should be negatively pressurized and equipped with air filters to prevent release of the pathogen from the laboratory. Selective media are designed to suppress the growth of unwanted bacteria and encourage the growth of the desired microbes. For example, bismuth sulfite agar is one medium used to isolate the typhoid bacterium, the gram-negative Salmonella typhi (T-f), from feces. Bismuth sulfite inhibits gram-positive bacteria and most gram-negative intestinal bacteria (other than S. Differential media make it easier to distinguish colonies of the desired organism from other colonies growing on the same plate. Similarly, pure cultures of microorganisms have Chapter 6 Microbial Growth 161 Enrichment Culture Because bacteria present in small numbers can be missed, especially if other bacteria are present in much larger numbers, it is sometimes necessary to use an enrichment culture. The medium (enrichment medium) for an enrichment culture is usually liquid and provides nutrients and environmental conditions that favor the growth of a particular microbe but not others. In this sense, it is also a selective medium, but it is designed to increase very small numbers of the desired type of organism to detectable levels. Suppose we want to isolate from a soil sample a microbe that can grow on phenol and is present in much smaller numbers than other species. If the soil sample is placed in a liquid enrichment medium in which phenol is the only source of carbon and energy, microbes unable to metabolize phenol will not grow. The culture medium is allowed to incubate for a few days, and then a small amount of it is transferred into another flask of the same medium. After a series of such transfers, the surviving population will consist of bacteria capable of metabolizing phenol. The bacteria are given time to grow in the medium between transfers; this is the enrichment stage. When the last dilution is streaked onto a solid medium of the same composition, only those colonies of organisms capable of using phenol should grow. A remarkable aspect of this particular technique is that phenol is normally lethal to most bacteria. Air pressure in the suit is higher than the atmosphere, preventing microbes from entering the suit. Q If a technician were working with pathogenic prions, how would material leaving the lab be rendered noninfectious Blood agar (which contains red blood cells) is a medium that microbiologists often use to identify bacterial species that destroy red blood cells. Sometimes, selective and differential characteristics are combined in a single medium.

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In specialized transduction treatment of scabies order 250mg lopinavir free shipping, however, only certain bacterial genes can be transferred. The phage carries this gene to a galactose-negative cell, which then becomes galactose-positive. Also, once the virus is inside, the synthesis and assembly of the new viral components are somewhat different, partly because of the differences between prokaryotic cells and eukaryotic cells. Finally, the mechanisms of maturation and release, and the effects on the host cell, differ in animal viruses and phages. A virus needs live host cells but must stop synthesis of host proteins, so the viral genes are translated. Research currently indicates that viruses use several mechanisms to inhibit expression of host cell genes. However, the receptor sites of animal cells are proteins and glycoproteins of the plasma membrane. The attachment sites of animal viruses are distributed over the surface of the virus, and the sites themselves vary from one group of viruses to another. As soon as one spike attaches to a host receptor, additional receptor sites on the same cell migrate to the virus. This could account for the individual differences in susceptibility to a particular virus. Understanding the nature of attachment can lead to the development of drugs that prevent viral infections. Many viruses enter into eukaryotic cells by receptor-mediated endocytosis (Chapter 4, page 97). These vesicles contain elements that originate outside the cell and are brought into the interior of the cell to be digested. Some animal viruses accomplish uncoating by the action of lysosomal enzymes of the host cell. Herpesviruses, papovaviruses, adenoviruses, and hepadnaviruses all follow this pattern of biosynthesis (table 13. Poxviruses are an exception because all of their components are synthesized in the cytoplasm. After Q attachment, viruses enter host cells by (a) receptor-mediated endocytosis 1 2 3 or (b) fusion of the viral envelope and cell membrane. Viral rNa functions as a template for synthesis of rNa polymerase, which copies - strand rNa to make mrNa in cytoplasm. Knowledge of viral replication phases is important for drug development strategies, and for understanding disease pathology. This enzyme is discussed later with the retroviruses, the only other family with reverse transcriptase. This enzyme copies the virus sense strand and makes an antisense strand (- strand), which serves as a template to produce additional + strands. Infectious hepatitis can be caused by a member of the picornaviridae, hepadnaviridae, or Flaviviridae. List the method of transmission, morphology, nucleic acid, and type of replication for these three viral families. Reoviridae Reoviruses were named for their habitats: the respiratory and enteric (digestive) systems of humans. Three serotypes are now known to cause respiratory tract and intestinal tract infections. Togaviruses are enveloped viruses; their name is from the Latin word for covering, toga. In other cases, the provirus is expressed and produces new viruses, which may infect adjacent cells. In oncogenic retroviruses, the provirus can also convert the host cell into a tumor cell; possible mechanisms for this phenomenon will be discussed later. Maturation and Release the first step in viral maturation is the assembly of the protein capsid; this assembly is usually a spontaneous process. A retrovirus may become a provirus that replicates in a latent state, and it may produce new retroviruses. Nonenveloped viruses are released through ruptures in the host cell plasma membrane. In contrast to budding, this type of release usually results in the death of the host cell. The relationship between cancers and viruses was first demonstrated in 1908, when virologists Wilhelm Ellerman and Olaf Bang, working in Denmark, were trying to isolate the causative agent of chicken leukemia. They found that leukemia could be transferred to healthy chickens by cell-free filtrates that contained viruses. Peyton Rous, working at the Rockefeller Institute in New York, found that a chicken sarcoma (cancer of connective tissue) can be similarly transmitted. Virus-induced adenocarcinomas (cancers of glandular epithelial tissue) in mice were discovered in 1936. Notice that the four budding viruses acquire their coats from the host plasma membrane. It has reverse transcriptase and is transmitted by the parenteral route (intravenous injection) or through sexual contact. The envelope protein is encoded by the viral genes and is incorporated into the plasma membrane of the host cell. The envelope lipid and carbohydrate are encoded by host cell genes and are present in the plasma membrane. After the sequence of attachment, entry, uncoating, and biosynthesis of viral nucleic acid and protein, the assembled capsid containing nucleic acid pushes through the plasma membrane. As a result, a portion of the plasma membrane, now the envelope, adheres to the virus. Oncogenes were first identified in cancer-causing viruses and were thought to be a part of the normal viral genome. Varmus received the 1989 Nobel Prize in Medicine for proving that the cancerinducing genes carried by viruses are actually derived from animal cells. Bishop and Varmus showed that the cancer-causing src gene in avian sarcoma viruses is derived from a normal part of chicken genes. Oncogenes can be activated to abnormal functioning by a variety of agents, including mutagenic chemicals, high-energy radiation, and viruses. Viruses capable of inducing tumors in animals are called oncogenic viruses, or oncoviruses. Transformed cells tend to be irregularly shaped, compared to normal cells, and they tend to exhibit certain chromosomal abnormalities, such as unusual numbers of chromosomes and fragmented chromosomes. These groups include the Adenoviridae, Herpesviridae, Poxviridae, Papovaviridae, and Hepadnaviridae. An autopsy revealed that the virus had been unwittingly introduced into the boy with the bone marrow transplant. For example, in this case, the health department recommends that everyone who ate at this convenience store in the previous 2 weeks receive hepatitis a vaccine and hepatitis a immunoglobulin. Viruses were originally named for the symptoms they caused, hence the name "hepatitis virus" for a virus that affects the liver (from Latin hepaticus). Molecular tools now allow viruses to be classified on the basis of genomes and morphology. Differentiating viruses based on their genetic information provides valuable information for treatment and prevention. Some retroviruses contain oncogenes; others contain promoters that turn on oncogenes or other cancer-causing factors. A virus can remain in equilibrium with the host and not actually produce disease for a long period, often many years. All of the human herpesviruses can remain in host cells throughout the life of an individual. The classic example of such a latent infection is the infection of the skin by Simplexvirus, which produces cold sores.

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Prostaglandins affect smooth muscles of the respiratory system and increase mucus secretion medicine zyrtec buy lopinavir 250mg otc. Collectively, all these mediators serve as chemotactic agents that, in a few hours, attract neutrophils and eosinophils to the site of the degranulated cell. Systemic Anaphylaxis At the turn of the twentieth century, two French biologists studied the responses of dogs to the venom of stinging jellyfish. Large doses of venom usually killed the dogs, but sometimes a few survived the injections. These surviving dogs were used for repeat experiments with the venom, and the results were surprising. Even a very tiny dose of the venom, one that should have been almost harmless, killed the dogs. They suffered difficulty in respiration, entered shock as their cardiovascular systems collapsed, and quickly died. Systemic anaphylaxis (or anaphylactic shock) can result when an individual sensitized to an antigen is exposed to it again. Even a small dose of the antigen in question may cause a systemic reaction in someone who is sensitized to it. Of course, the attached IgE monomers will not all be specific for the same antigen. But when an antigen such as plant pollen encounters two adjacent antibodies of the same appropriate specificity, it can bind to one antigen-binding site on each antibody, bridging the space between them. These mediators cause the unpleasant and damaging effects of an allergic reaction. Our bodies are complex sets of ecosystems, with segments that come into contact with the outer world, each having its own microbial population. However, a change in microbiota can result in dysbiosis, an imbalance that causes adverse effects in the human. For example, Clostridium difficile, or C-diff, is usually a minor component of the normal gut microbiota. But when antibiotic therapy kills normal microbiota, C-diff proliferates, producing two toxins that create significant inflammation and gas production in the intestines. Rationale for this hypothesis hinges on the fact that some metabolic products of normal microbiota, such as butyrates, exert an antiinflammatory effect on the body. Researchers hypothesize that this excess could result from a disruption in the balance of normal microbiota that would usually help keep inflammatory cytokines under control. Studies have demonstrated that the microbiome may not recover its full diversity after antibiotic treatment, which may lead to loss of organisms that would keep inflammation under control. Thomas Louie at the University of Calgary holds a dish of "poop pills" used for fecal transplantation. Fecal transplants involve taking gut microbiota from a healthy individual (usually a family member) and then transplanting it into the patient via an enema, gastroscope, or nasojejunal tube, which is placed through the nose and runs down to the small intestine. Researchers are working on ways to transplant microbiota in a more palatable fashion. Thomas Louie, an infectious disease specialist at the University of Calgary, has developed a method to deliver the microbiota in pills surrounded by a triple layer of gel, to prevent breakdown in the stomach. The release of mediators causes peripheral blood vessels throughout the body to enlarge, resulting in a drop in blood pressure (shock). Treatment usually involves self-administration with a preloaded syringe of epinephrine, a drug that constricts blood vessels and raises the blood pressure. In the United States, 50 to 60 people die each year from anaphylactic shock caused by insect stings. In these individuals, the penicillin, which is a hapten (it cannot induce antibody formation by itself; see Chapter 17), combines with a carrier serum protein. Patients who have a positive skin test can be desensitized (see page 521) by an orally administered series of increasing doses of penicillin V. The desensitization is effective only for an uninterrupted penicillin series immediately following the procedure. Allergy to penicillin also includes risk from exposure to some related drugs, such as carbapenem (page 558). In allergies involving the upper respiratory system, such as hay fever, sensitization usually involves mast cells in the mucous membranes of the upper respiratory tract. Antihistamine drugs, which compete for histamine receptor sites, are often used to treat these symptoms. Symptoms such as wheezing and shortness of breath are caused by the constriction of smooth muscles in the bronchial tubes. For unknown reasons, asthma is becoming a near epidemic, affecting about 10% of children in Western society, although they often outgrow it. The hygiene hypothesis, described previously, may be a factor in the increased incidence of asthma. Mental or emotional stress can be a contributing factor in precipitating an attack. Xolair (omalizumab) is a newly available drug but is a very expensive treatment for severe allergic asthma. Antigens that enter the body via the gastrointestinal tract can also sensitize an individual. Frequently, so-called food *Dander is a general term for microscopic particles from the fur or skin of animals. People with allergies to mice, gerbils, and similar small animals are more likely to be allergic to components of urine accumulating in cages. ChaPter 19 Disorders Associated with the Immune system 521 although food labels should indicate their presence, they may be difficult to avoid in practice. A food product may have come into contact with a food allergen through processing machinery or cookware previously used for other foods. Food and Drug Administration report, 25% of bakery, ice cream, and candy products tested positive for peanut allergens even though peanuts were not listed on the required product labels. In the United States it is estimated that 200 persons a year die of severe allergic reactions to foods. Preventing Anaphylactic reactions Some individuals experience an allergic reaction after eating an assortment of foods and may not know exactly what food they are sensitive to . These tests, which are also used for allergies other than those to foods, involve inoculating small amounts of the suspected antigen just beneath the epidermis of the skin. Sensitivity to the antigen is indicated by a rapid inflammatory reaction that produces redness, swelling, and itching at the inoculation site. Once the responsible antigen has been identified, the person can either try to avoid contact with it or undergo desensitization. This procedure usually consists of a series of gradually increasing dosages of the antigen carefully injected beneath the skin. The objective is to cause the production of IgG rather than IgE antibodies in the hope that the circulating IgG antibodies will act as blocking antibodies to intercept and neutralize the antigens before they can react with cell-bound IgE. A light scratch is made with a needle to allow the substances to penetrate the skin. Reddening and swelling at the site identify the substance as a probable cause of an allergic reaction. For example, many people are unable to digest the lactose in milk because they lack the enzyme that breaks down this disaccharide milk sugar. The lactose enters the intestine, where it osmotically retains fluid, causing diarrhea. Gastrointestinal upset is a common symptom of food allergies, but it can also result from many other factors. Hives are more characteristic of a true food allergy, and ingestion of the antigen may result in systemic anaphylaxis. Death has even resulted when a person sensitive to fish ate french fries that had been prepared in oil previously used to fry fish. Skin tests are not reliable indicators for diagnosing food-related allergies, and completely controlled tests for hypersensitivity to ingested foods are very difficult to perform. Only eight foods are responsible for 97% of food-related allergies: eggs, peanuts, tree-grown nuts, milk, soy, fish, wheat, and peas.

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Oral bacteria convert sucrose and other carbohydrates into lactic acid symptoms 10dpo purchase lopinavir with a visa, which in turn attacks the tooth enamel. Some other species of streptococci are also cariogenic but play a lesser role in initiating caries. In the production of dextran, the bacteria first hydrolyze sucrose into its component monosaccharides, fructose and glucose. Accumulations of bacteria and dextran adhering to the teeth make up dental plaque. The bacterial population of plaque may harbor over 400 bacterial species but is predominantly streptococci and filamentous members of the genus Actinomyces. On protected areas of the teeth, plaque accumulations 710 Part Four Microorganisms and Human Disease (a) S. Although saliva contains nutrients that encourage the growth of bacteria, it also contains antimicrobial substances, such as lysozyme, that help protect exposed tooth surfaces. It protects teeth by virtue of its flushing action, its phagocytic cells, and immunoglobulin content. Localized acid production within deposits of dental plaque results in a gradual softening of the external enamel. This Plaque Enamel Dentin Pulp Bone Root Decay is the reason for fluoridation of water and toothpastes, a significant factor in the decline in tooth decay in the United States. If the initial penetration of the enamel by caries remains untreated, bacteria can penetrate into the interior of the tooth. The composition of the bacterial population involved in spreading the decayed area from the enamel into the dentin is entirely different from that of the population initiating the decay. However, these very prolific lactic acid producers are important in advancing the front of the decay once it has become established. Almost any member of the normal microbiota of the mouth can be isolated from the infected pulp and roots. Once this stage is reached, root canal therapy is required to remove the infected and dead tissue and to provide access for antimicrobial drugs that suppress renewed infection. If untreated, the infection may advance from the tooth to the soft tissues, producing dental abscesses caused by mixed bacterial populations that contain many anaerobes. Although dental caries is probably one of the more common infectious diseases in humans today, it was scarce in the Western world until about the seventeenth century. The introduction of table sugar, or sucrose, into the diet is highly correlated with our present level of caries in the Western world. People living on high-starch diets (starch is a polysaccharide of glucose) have a low incidence of tooth decay unless sucrose is also a significant part of their diet. The contribution of bacteria to tooth decay has been shown by experiments with germ-free animals. However, if sucrose is ingested only at regular mealtimes, the protective and repair mechanisms of the body are usually not overwhelmed. Sugar alcohols, such as mannitol, sorbitol, and xylitol, are not cariogenic; xylitol even appears to inhibit carbohydrate metabolism in S. This is why these sugar alcohols are used to sweeten "sugarless" candies and chewing gum. The best strategies for preventing dental caries are a minimal ingestion of sucrose; brushing, flossing, and professional cleaning to remove plaque; and the use of fluoride. Professional removal of plaque and tartar at regular intervals lessens the progression to periodontal disease. The roots of the tooth are protected by a covering of specialized connective tissue called cementum. As the gums recede with age or with overly aggressive brushing, the formation of caries on the cementum becomes more common. It has been shown experimentally that gingivitis will appear in a few weeks if brushing is discontinued and plaque is allowed to accumulate. An assortment of streptococci, actinomycetes, and anaerobic gram-negative bacteria predominate in these infections. Periodontitis Gingivitis can progress to a chronic condition called periodontitis, an insidious condition that generally causes little discomfort. Use the table below to identify infections that could cause persistent sore, swollen, red, or bleeding gums, as well as tooth pain or sensitivity and bad breath. This gram-negative rod grown on blood agar accounts for nearly one-quarter of cases. Disease Dental Caries Periodontal Disease Acute Necrotizing Ulcerative Gingivitis Pathogen Primarily Streptococcus mutans Various, primarily Porphyromonas spp. Prevotella intermedia Symptoms Discoloration or hole in tooth enamel Bleeding gums, pus pockets Pain chewing, halitosis treatment remove decayed area remove damaged area; antibiotics remove damaged area; metronidazole Prevention Brushing, flossing, reducing dietary sucrose Plaque removal Brushing, flossing 35% of adults suffer from periodontitis, which is increasing in incidence as more people retain their teeth into old age. The bone and tissue that support the teeth are destroyed, eventually leading to loosening and loss of the teeth. Because these pathogens are usually anaerobic, treatment with oxidizing agents, debridement, and the administration of metronidazole or antibodies may be temporarily effective. Why are "sugarless" candies and gum, which actually contain sugar alcohols, not considered cariogenic Microorganisms can penetrate into the intestinal mucosa and grow there, or they can pass through to other systemic organs. ChaPter 25 Microbial Diseases of the Digestive System 713 Both infections and intoxications often cause diarrhea, which most of us have experienced. Both types of digestive system diseases are also frequently accompanied by abdominal cramps, nausea, and vomiting. Diarrhea and vomiting are both defensive mechanisms designed to rid the body of harmful material. The general term gastroenteritis is applied to diseases causing inflammation of the stomach and intestinal mucosa. It is estimated that mortality from childhood diarrhea could be halved by oral rehydration therapy (replacement of lost fluids and electrolytes). This is usually a solution of sodium chloride, potassium chloride, glucose, and sodium bicarbonate to replace lost fluids and electrolytes. This has been found to reduce the duration and severity of diarrheal episodes and even help prevent future episodes for 2 or 3 months. Public health departments often determine the incidence of diarrhea in the population by receiving weekly reports on the sales of oral rehydration preparations. Organisms incubate in food (temperature abuse) long enough to form and release toxins. Staphylococcal Food Poisoning (Staphylococcal enterotoxicosis) A leading cause of gastroenteritis is staphylococcal food poisoning, an intoxication caused by ingesting an enterotoxin produced by S. Staphylococci are comparatively resistant to environmental stresses, as discussed on page 309. Resistance to high osmotic pressures helps them grow in foods, such as cured ham, in which the high osmotic pressure of salts inhibits the growth of competitors. If the microbes are allowed to incubate in the food, a situation called temperature abuse, they reproduce and release enterotoxin into the food. The production of the toxin of serological type A (which is responsible for most cases) is often correlated with the production of an enzyme that coagulates blood plasma. No direct pathogenic effect can be attributed to the enzyme, but it is useful in the tentative identification of types that are likely to be virulent. Generally, a population of about 1 million bacteria per gram of food will produce enough enterotoxin to cause illness. The growth of the microbe is facilitated if the competing microorganisms in the food have been eliminated-by cooking, for example. It is also more likely to grow if competing bacteria are inhibited by a higher-than-normal osmotic pressure or by a relatively low moisture level. Competing microbes are minimized in custards by the high osmotic pressure of sugar and by cooking.

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If after 2 minutes the F2 cell now becomes thr1 and leu1 internal medicine buy cheap lopinavir 250 mg on line, the order of these two genes on the chromosome must be thr, leu. Animations Conjugation: overview, F Factor, hfr Conjugation, Chromosome Mapping Transduction in Bacteria A third mechanism of genetic transfer between bacteria is transduction. All genes contained within a bacterium infected by a generalized transducing phage are equally likely to be packaged in a phage coat and transferred. In another type of transduction, called specialized transduction, only certain bacterial genes are transferred (see page 372). F+ cell (a) When an F factor (a plasmid) is transferred from a donor Recombination between F factor and chromosome, occurring at a specific site on each Insertion of F factor into chromosome Integrated F factor F+ cell Hfr cell (b) When an F factor becomes integrated into the chromosome of an F+ cell, it makes the cell a high frequency of recombination (Hfr) cell. Plasmids and Transposons Plasmids and transposons are genetic elements that provide additional mechanisms for genetic change. They occur in both prokaryotic and eukaryotic organisms, but this discussion focuses on their role in genetic change in prokaryotes. They are found mainly in bacteria but also in some eukaryotic microorganisms, such as Saccharomyces cerevisiae. The F factor is a conjugative plasmid that carries genes for sex pili and for the transfer of the plasmid to another cell. Although plasmids are usually dispensable, under certain conditions genes carried by plasmids can be crucial to the survival and growth of the cell. For example, dissimilation plasmids code for enzymes that trigger the catabolism of certain unusual sugars and hydrocarbons. Some species of Pseudomonas ChaPter 8 Microbial Genetics 231 bp1 0 90 10 80 3480 kbp 70 20 1160 kbp 30 of bacteriocins, toxic proteins that kill other bacteria. These plasmids have been found in many bacterial genera, and they are useful markers for the identification of certain bacteria in clinical laboratories. Resistance factors (R factors) are plasmids that have significant medical importance. They were first discovered in Japan in the late 1950s after several dysentery epidemics. The numbers inside the circle indicate the number of minutes it takes to transfer the genes during mating between two cells; the numbers in colored boxes indicate the number of base pairs. How many minutes of conjugation would be needed to transfer genes for membrane synthesis on this chromosome Such specialized capabilities permit the survival of those microorganisms in very diverse and challenging environments. Because of their ability to degrade and detoxify a variety of unusual compounds, many of them are being investigated for possible use in the cleanup of environmental wastes. Other plasmidencoded toxins include the exfoliative toxin of Staphylococcus aureus, Clostridium tetani neurotoxin, and toxins of Bacillus anthracis. Different R factors, when present in the same cell, can recombine to produce R factors with new combinations of genes in their r-determinants. In some cases, the accumulation of resistance genes within a single plasmid is quite remarkable. Carried on this plasmid are resistance genes for sulfonamides, streptomycin, chloramphenicol, and tetracycline, as well as genes for resistance to mercury. This particular plasmid can be transferred between a number of enteric genera, including Escherichia, Klebsiella, and Salmonella. R factors present very serious problems for treating infectious diseases with antibiotics. The widespread use of antibiotics in medicine and agriculture (see the box in Chapter 20 on page 573) has led to the preferential survival (selection) of bacteria that have R factors, so populations of resistant bacteria grow larger and larger. The transfer of resistance between bacterial cells of a population, and even between bacteria of different genera, also contributes to the problem. The ability to reproduce sexually with members of its own species defines a eukaryotic species. However, a bacterial species can conjugate and transfer plasmids to other species. Nonconjugative plasmids may be transferred from one cell to another by inserting themselves into a conjugative plasmid or a chromosome or by transformation when released from a dead cell. Insertion is made possible by an insertion sequence, which will be discussed shortly. In the 1950s, American geneticist Barbara McClintock discovered transposons in corn, but they occur in all organisms and have been studied most thoroughly in microorganisms. They may move from one site to another site on the same chromosome or to another chromosome or plasmid. As you might imagine, the frequent movement of transposons could wreak havoc inside a cell. For example, as transposons move about on chromosomes, they may insert themselves within genes, inactivating them. The frequency of transposition is comparable to the spontaneous mutation rate that occurs in bacteria-that is, from 10-5 to 10-7 per generation. Following isolation, the pathogen was also found to be resistant to a number of different antibiotics. Researchers soon discovered that these bacteria acquired resistance through the spread of genes from one organism to another. R factors carry genes that confer upon their host cell resistance to antibiotics, heavy metals, or cellular toxins. ChaPter 8 Microbial Genetics 233 All transposons contain the information for their own transposition. Complex transposons also carry other genes not connected with the transposition process. Transposons with antibiotic resistance genes are of practical interest, but there is no limitation on the kinds of genes that transposons can have. Thus, transposons provide a natural mechanism for the movement of genes from one chromosome to another. Furthermore, because they may be carried between cells on plasmids or viruses, they can also spread from one organism-or even species-to another. For example, vancomycin resistance was transferred from Enterococcus faecalis to Staphylococcus aureus via a transposon called Tn1546. The tranposase gene is bounded at each end by inverted repeat sequences that function as recognition sites for the transposon. Diversity provides the raw material for evolution, and natural selection provides its driving force. Natural selection will act on diverse populations to ensure the survival of those fit for that particular environment. The different kinds of microorganisms that exist today are the result of a long history of evolution. Microorganisms have continually changed by alterations in their genetic properties and acquisition of adaptations to many different habitats. The base pairing of codon and anticodon at the ribosome results in specific amino acids being brought to the site of protein synthesis. Genetics is the study of what genes are, how they carry information, how their information is expressed, and how they are replicated and passed to subsequent generations or other organisms. Phenotype is the expression of the genes: the proteins of the cell and the properties they confer on the organism. At the replication fork, the leading strand is synthesized continuously and the lagging strand discontinuously. Regulating protein synthesis at the gene level is energy-efficient because proteins are synthesized only as they are needed. When cells are exposed to a particular end-product, the synthesis of enzymes related to that product is repressed.