Micro Biology- Exam 3

There were 100 new cases of syphilis last year in a given population of 100,000 people. At that time, 500 people in this population already had syphilis. The incidence of syphilis in this population is __________.

100 per 100,000 *** Incidence of a disease is defined as the number of new cases of the disease in a given area or population during a given period of time. Therefore, the incidence of syphilis in this population is 100 per 100,000.

Sulfonamide drugs inhibit microbial growth by disrupting metabolic pathways. What general mechanism do these drugs use?

Competitive inhibition *** Sulfonamides bind to the active site of an enzyme in the metabolic pathway responsible for producing folic acid, a key step in nucleotide production.

Refrigeration is an effective germicidal method.

False

The (incubation/morbidity/prodromal) period is the time between infection and the occurrence of the first symptoms or signs of the disease.

Incubation

A new drug blocks the adhesins on the surface of a bacterial pathogen. What would likely be the major effect of this drug?

It will prevent infection by this pathogen. *** Without adhesins to help them attach to host cells and tissues, pathogens generally cannot resist the defenses of the body long enough to cause an infection or disease.

PART A Transcription produces which of the following? PART B According to the animation, which of the following makes mRNA from the information stored in a DNA template? PART C Ribosomes contain which of the following? PART D Which of the following is involved in bringing amino acids to the ribosomes? PART E Which of the following can be translated into protein?

PART A mRNA, tRNA, and rRNA are all produced by transcription. PART B RNA polymerase PART C rRNA PART D tRNA PART E mRNA

While investigating a newly discovered Gram-negative bacterium, you find that when the bacteria die, the host experiences severe fever and inflammation. You suspect that the bacterium has __________ in its outer wall membrane.

lipid A *** Lipid A is the toxic portion of the lipopolysaccharide (LPS) found in the outer membrane of Gram-negative bacteria. Lipid A stimulates the body to release chemicals that can cause fever, inflammation, diarrhea, hemorrhaging, shock, and blood coagulation.

A base substitution changes a UCG codon to UAG. This is an example of a ________ mutation.

nonsense

Which of the following types of mutations creates a stop codon where one did not exist before?

nonsense mutation

Damage to the cell wall will adversely affect a bacterial cell by making it more susceptible to __________.

osmotic pressure *** Without a strong, functional cell wall, the bacterial cell cannot resist sudden changes in osmotic pressure and can die as a result.

The tetracyclines interfere with

protein synthesis.

Persons with asymptomatic infections may be (contaminants/reservoirs/zoonoses) of disease.

reservoirs

Handwashing with regular soap is effective because __________.

the hydrophobic end of the soap molecule breaks up oily deposits and the hydrophilic end of the molecule attracts water. This combination makes soap a good degerming agent. *** Degerming is the removal of microbes from a surface by scrubbing. The combination of soap and scrubbing during handwashing will remove microbes from the skin's surface.

The incidence of tuberculosis in the year 2000 in the United States was 12.43/100,000 cases. This means

there were 12.43 new cases of tuberculosis for every 100,000 people in the United States in the year 2000.

Genetic elements known as promoters are initiation points in the process of

transcription.

RNA polymerase is primarily responsible for

transcription.

Bacteriophages are important for which of the following processes?

transduction

A patient contracted a disease just by being in the same room with an infected individual for an extended period of time. Which of the following modes of disease transmission is most applicable in this situation?

vehicle transmission *** Any of these modes of transmission is theoretically possible. However, evidence suggests that the infectious agent was probably spread through the air, a type of vehicle transmission.

Which of the following is an example of vehicle transmission?

drinking contaminated water

Which of the following is NOT a factor in determining the potential of a new antimicrobial?

duplication of existing antimicrobial mechanism of action

Quaternary ammonium compounds are disinfectants effective against

enveloped viruses.

If the sequence of DNA is CCGATTAG and it becomes CCGAATTAG, what type of mutation has occurred?

frameshift mutation

An epidemiologist collects drinking glasses, tissues, and bed sheets from the apartment of an individual infected with a particular disease. Which of the following modes of transmission is being investigated for this disease?

indirect contact transmission *** Inanimate objects, also known as fomites, are instrumental in the spread of pathogens by indirect contact transmission.

Which of the following is NOT a mode of action of antimicrobial drugs?

inhibition of flagella formation *** Antimicrobial drugs can inhibit protein or nucleic acid synthesis and can also inhibit the formation of the cell wall. Inhibition of flagella formation might be an indirect result of the action of some antimicrobial drugs, but it is not a direct target.

_____ cells would be expected to be the most susceptible to the action of polyene drugs such as amphotericin B, while _____ cells would be the least susceptible.

- Fungal; bacterial *** Fungal cells are the most susceptible to the activity of polyene drugs due to the presence of ergosterol in their cytoplasmic membranes. Bacterial cells are the least susceptible because they usually have no sterols in their membranes.

What kind of mutation is characterized by having no effect on the final protein?

- Silent mutation *** Silent mutations involve a change in the original genetic code that does not change the final amino acid sequence.

How do the antiviral drugs amantadine and rimantadine work?

- They prevent viral uncoating by increasing the pH in phagolysosomes. *** Amantadine and rimantadine increase the pH inside phagolysosomes, preventing viruses that require low pH from uncoating.

All of the following might lead to a disease caused by an opportunistic pathogen except __________.

- an encounter with an infected animal *** Opportunistic pathogens are usually normal microbiota that become pathogenic only under certain conditions. Since the pathogens are found on the host, an encounter with an infected animal would not lead to a disease caused by an opportunistic pathogen.

Which of the following is NOT associated with microbial mechanisms of resistance?

- denaturation of proteins *** Proteins are not denatured by antimicrobial drugs.

A particular microbe gains resistance to gentamicin. You might also expect this microbe to exhibit resistance against __________.

- streptomycin *** Since streptomycin and gentamicin are members of the same group of antimicrobial drugs (the aminoglycosides), one might expect that resistance to both drugs could develop simultaneously through the phenomenon of cross-resistance.

Using a broad-spectrum antibiotic to treat an infection might seem like a good idea at first, but its use can allow unaffected members of the microbiome to cause what sort of infection?

- superinfections ***Superinfections are caused when some microbiota are unaffected by an antimicrobial drug and find themselves unchallenged by their usual neighbors who are affected. The sudden lack of competition for resources results in microbial overgrowth.

What major cellular feature that might be targeted by antimicrobial drugs is found in both bacteria and fungi but not in human cells?

- A cell wall *** Both bacteria and fungi have cell walls. One antimicrobial strategy is to prevent the synthesis of cell walls. Humans do not have cell walls and are thus unaffected.

How do the enzymes hyaluronidase and collagenase increase bacterial virulence?

- By allowing bacteria to invade deeper into tissues, making the infection more likely to cause disease *** Hyaluronidase and collagenase allow bacteria to penetrate deeper into tissues.

Mycoplasmas are bacteria that do not contain cell walls. These bacteria are naturally resistant to which of the following?

- Methicillin *** Methicillin is a beta-lactam and targets growing peptidoglycan layers in the cell wall. Since mycoplasmas do not have a cell wall, they are naturally resistant to beta-lactams.

Which of the following types of diseases develops rapidly and only lasts a short time?

Acute disease *** Acute diseases develop rapidly and last a relatively short time.

An antimicrobial that inhibits bacterial cell wall synthesis will result in which of the following?

Bacterial cells become more susceptible to osmotic pressure

Drugs known as beta-lactams interfere with bacterial (DNA/folic acid/cell wall) synthesis.

Cell wall

The ribosomes of bacteria differ significantly from our own, making them a prime target for antimicrobial drugs. Which commonly prescribed antimicrobial for eye infections blocks the formation of peptide bonds in prokaryotes?

Chloramphenicol *** Chloramphenicol blocks formation of new peptide bonds in prokaryotes.

Aldehydes are highly effective germicidal agents because they damage (lipids/cell walls/DNA)

DNA

The viral pathogen that causes cold sores can remain inactive in the body for a long time between disease outbreaks. How is this disease classified?

It is a latent disease. *** A latent disease remains inactive in the body for a long period of time.

PART A What is meant when a bacterium is said to become "resistant" to an antibiotic? PART B When a patient is treated with antibiotics, __________. PART C The process of acquiring antibiotic resistance by means of bacteriophage activity is called PART D Which of the following mutations would not result in antibiotic resistance? PART E R-plasmids are most likely acquired via

PART A The bacterium is neither killed nor inhibited by the antibiotic. PART B the drug will kill or inhibit the growth of all of the sensitive bacterial cells PART C transduction PART D Silent mutation PART E bacterial conjugation

PART A Competent cells are cells that PART B Mice that are injected with only the R strain of Streptococcus pneumoniae PART C What characteristic of the S strain allows it to evade the immune system of the mice? PART D What most likely explains the recovery of live S strain cells from a mouse injected with heat-killed S strain mixed with live R strain cells? PART E Which finding is most surprising from Griffith's experiments?

PART A can take up DNA from their surrounding environment and integrate it into their own chromosomes by recombination PART B stay healthy, because their immune systems can kill this strain easily. PART C The cells have a capsule. PART D The R strain picked up the S strain DNA, enabling it to produce a capsule. PART E S strain cells are isolated from the blood of mice infected with heat-killed S strains and live R strains.

PART A Certain traits that allow pathogens to create infection and cause disease are termed PART B Which of the following enzymes breaks down the "glue" that holds cells together? PART C Which of the following virulence factors would be found in Staphylococcus aureus? PART D How do fibrinolysins enhance a pathogen's virulence?

PART A virulence factors. PART B Hyaluronidase PART C Staphylokinase PART D They break down fibrin proteins that are involved in clot formation, allowing the cells to penetrate deep into damaged skin.

PART A A recombinant cell PART B What is the hallmark of all horizontal gene transfers? PART C Which of the following is an example of horizontal gene transfer in bacteria?

PART A - is a cell that receives DNA from an outside source and incorporates it into its own. PART B - Transfer of DNA between organisms of the same generation PART C - Transduction, conjugation, and transformation

PART A Expected prevalence of a disease is PART B In the sixth segment of the animation, why is the disease epidemic in North America? PART C In the last segment of the animation, how many regions of the world experience the pandemic during April of year four? PART D In the last segment of the animation, when does the first epidemic occur? PART E If a disease occurs at a fairly stable rate, it is said to be

PART A the expected occurrence of a disease based on past observations. PART B The disease occurs at a higher rate than what would normally be expected in this region. PART C Five PART D January of year three PART E endemic.

What term describes a procedure that destroys all microbes?

Sterilization *** Sterilization refers to the removal or destruction of all microbes, including viruses and bacterial endospores, in or on an object.

***** Mary loved having her own garden and would often spend many hours tending to its care. She was meticulous in watering the plants, pulling the dreaded weeds, and harvesting the fruits and vegetables as they ripened. Her garden consisted of corn, tomatoes, green beans, okra, zucchini, squash, lima beans, watermelon, and cantaloupe. Often, the garden would produce much more than Mary and her daughter, Sue, could eat. Rather than waste the delicious food, the ladies would spend hours on the weekend canning the excess vegetables and fruit. It was something they had done for many years. On this particular occasion, Sue noticed that the pressure cooker, the instrument used to sterilize the canned food, did not seem to be acting quite right, but the cans were hot when they came out so she figured everything would be okay.Several months after their weekend of canning, the ladies invited the entire family over for Thanksgiving dinner. The meal consisted of turkey, ham, chicken, macaroni and cheese, rolls, spinach salad, tomatoes, corn, lima beans, green beans, and okra. All of the vegetables were the ones they had previously canned from their garden. For dessert, they had pecan pie and vanilla ice cream. The next day, while most of the family was out shopping, four of the family members were home with blurred vision, dry mouth, and muscle weakness. Mary called the family physician, Dr. Franklin, who told her to take the sick individuals to the emergency room, and he would meet them there. Upon arrival at the ER, Dr. Franklin asked what the family members had eaten for the meals before they developed the symptoms. The common foods that all of them ate were the chicken, the ham, the tomatoes, the green beans, and the spinach salad. The doctor determined that the family was suffering from botulism food poisoning. In the United States, foodborne botulism happens in 15% of cases each year, frequently from foods with a low acidity. He was suspicious of the green beans and tomatoes, even though tomatoes are highly acidic. Dr. Franklin also said that using proper methods of microbial control could have prevented their illness. Part A Which of the following is an example of microbial control? Part B What was the MOST likely source of the family's botulism food poisoning? ***** Miraculously, all four family members who had suffered from botulism food poisoning recovered fully from their illness. They were able to go home, but they were warned to be careful about ingesting canned goods in the future. Mary was thankful that the family members were okay. Part C Botulism food poisoning is a preventable illness if special precautions are taken during food preparation. In this case, what could Sue have done to prevent the outbreak of botulism? Part D Which of the following best explains why the pressure cooker is so important in the canning process? ***** In this case study, the pressure cooker used in the canning process for garden vegetables is essential to the prevention of illness and disease. Pressure cookers and autoclaves rely on moist heat for the sterilization of materials. Moist heat is an example of a physical method of control, but it is not the only method of controlling the growth of microorganisms. Chemical methods may also be employed, depending on the situation. Before choosing a method of control, you must consider the microbes involved and anything else that your chosen method may affect. Part E Use of moist heat can control microbial growth in many circumstances, but heat-sensitive items and those susceptible to moisture cannot be sterilized in this manner. Which of the following correctly describes a method of physical control used to control microbial growth on or in such items? Part F Sodium nitrate and sodium nitrite are added to many meat products, such as ham, bacon, hot dogs, and sausage. These additives help to prevent the growth of Clostridium botulinum by inhibiting certain iron-containing enzymes of the organism. This is an example of chemical food preservation. Which of the following correctly describes a method of chemical control used to control microbial growth?

Part A - Sue washes off the vegetables before serving them in a meal. - Sue uses bleach to clean the kitchen counters. - Mary places leftovers in the refrigerator after the meal. ***Methods of microbial control can be physical or chemical. Washing vegetables will physically remove any organisms that may be on them. Bleach is used very often as a surface disinfectant, both in the everyday household and on an industrial level. It is effective at controlling microbial growth because it interferes with cellular enzymes. Refrigeration is useful because the low temperatures found in the ordinary refrigerator (0 to 7 degrees C) inhibit the metabolic rate of most microbes to the point that they cannot reproduce or synthesize toxins. Most pathogenic bacteria will not grow at refrigerator temperatures. Part B - The family consumed botulism toxin in the canned green beans. ***The canned green beans are the most likely culprit for botulism toxin. C. botulinum is a soil microbe that could be found on green beans. If the canned beans were not prepared and canned properly, then the organism would be able to survive. It is less likely that C. botulinum could survive in the canned tomatoes, because tomatoes are very acidic. The family ingested the toxin with the green beans, and that is why they suffered from botulism food poisoning. Part C - Sue noticed that the pressure cooker was malfunctioning during the canning process. She should have fixed the instrument, borrowed a properly working one, or purchased a new pressure cooker. - Sue could have boiled the food for at least 10 minutes before serving it to her family members. ***The illness in this case study was most likely caused by the failure of the pressure cooker to properly sterilize the canned vegetables. When Sue realized it was not working, she should have replaced it with a pressure cooker that was functioning properly. Boiling the food for at least 10 minutes prior to serving may have also prevented the illness; however, boiling is not a foolproof method. Finally, she could have discarded only the cans that she knew were not sealed properly in the pressure cooker. The ones that were properly pressurized were fine to use for Thanksgiving dinner. Part D - A pressure cooker utilizes steam to create a higher-pressure environment that allows the food to cook at higher temperatures than normal. The higher temperatures kill most contaminating microbes and endospores and therefore effectively sterilize the food. *** Pressure cookers rely on the relationship between pressure and temperature. As you increase pressure, you increase the temperature at which liquids boil. The increase in pressure in a pressure cooker or an autoclave is a result of the production of steam within the chamber. Complete sealing of the chamber is essential for proper functioning of either piece of equipment. As the pressure rises, the temperature will also increase. This allows for sterilization of many solids and small volumes of liquids within a very short period of time. When working properly, an autoclave or a pressure cooker reaches temperatures as high as 121 degrees C at 15 psi, which is hot enough to kill all organisms (except prions) and their endospores in about 15 minutes. This is an extremely useful sterilization technique for items that are not destroyed by high heat or moisture. Part E - Filtration is the passage of a liquid or a gas through a screen like material with pores small enough to retain microorganisms. A vacuum is typically used to force the liquid through the mesh, and then the sterile liquid or gas is collected in a sterile container on the other side. - Nonionizing radiation, such as UV light, has a wavelength longer than that of ionizing radiation. The wavelengths of UV light are absorbed by cellular DNA in organisms directly exposed to the light. - Desiccation is a process that removes water from microorganisms, leaving them unable to grow or reproduce, but still viable. - Osmotic pressure is a process that uses high concentrations of salts and sugars to preserve food. *** Physical methods of microbial control in food preservation have been around since the Stone Age. Heat can either be moist or dry, but moist heat is more effective for microbial control in short durations. Moist heat kills microorganisms by denaturing their proteins. Dry heat kills by the oxidation effect and requires longer times at higher heat because heat is transferred from the air more slowly than from water. Filtration is a method that can be used for heat-sensitive solutions and involves a porous membrane that keeps the microbes out of the sterilized solution. Low temperatures can also be used to reduce the level of microbes, but typically this method does not completely kill them. Desiccation removes water from the microbes that is necessary for metabolism and reproduction. Osmotic pressure methods rely on high concentrations of salts and sugars to create a hypertonic environment that causes water to exit the cell. Finally, radiation uses different wavelengths of energy to kill microorganisms. Radiation can be ionizing (high energy; forms hydroxyl radicals that damage DNA) or nonionizing (low energy; damages DNA via bonding changes). Part F - Surface-active agents, or surfactants, decrease surface tension among molecules of a liquid. - Phenolics exert antimicrobial activity by injuring lipid-containing plasma membranes, which causes the cellular components to leak out of the cell. - Alcohols exert their action by denaturing proteins and dissolving lipids. ***There are multiple types of chemical agents that can be used to disinfect body tissues or inanimate objects. When choosing an agent, one should consider the groups of organisms that the disinfectant is effective against, the effective concentration, the nature of the material being disinfected, and how easily the disinfectant will come into contact with the microbes. The major effects of disinfection are disruption of plasma membranes, protein/enzyme denaturation, alteration of cellular components, lipid dissolution, and metabolic inhibition. Remember, most disinfectants only slow the growth of microbes. They are not as effective at killing microbes as most physical methods!

What is the purpose of Koch's postulates?

To demonstrate that a particular microbe causes a specific disease *** Koch's postulates link a microbe to a disease.

There are relatively few antifungal medications available compared to antibacterial drugs.

True

Which form of radiation is most likely to control microbes in a barbershop or hair salon?

Ultraviolet *** Ultraviolet or UV radiation does not penetrate well, but effectively treats surfaces of objects such as barber's shears. This form of radiation is also effective in treating thin layers of transparent fluids such as water.

If someone contracts food poisoning from drinking contaminated raw milk, what type of transmission has occurred?

Vehicle transmission *** Transmission via contaminated food is an example of vehicle transmission.

In the lab, you transform E. coli with a plasmid containing a gene for ampicillin. After the transformation, bacterial cells grew on media containing ampicillin and control media without ampicillin. Does this mean the transformation was a success?

Yes, the growth of bacteria on media containing ampicillin indicates that these cells were transformed.

A reservoir is

a source of microbial contamination.

Disinfectants that damage membranes include

both alcohol and phenolics.

Alcohols are used for

both antisepsis and disinfection.

Which of the following are considered to be frameshift mutations?

both deletions and insertions

Bacitracin blocks the transport of NAG and NAM across the cytoplasmic membrane to the cell wall. Like other antimicrobials that block cell wall synthesis, this would result in weak cell walls and __________.

cell lysis due to the effect of osmotic pressure

Which of the following is considered a mechanical vector transmission?

cockroach transmission of Shigella

A nurse rubbing a section of skin with an alcohol pad prior to an injection is an example of _____.

degerming *** Even something as simple as washing your hands can be an effective degerming method.

Washing dishes in the dishwasher with detergent and hot water is a ________ process.

degerming and disinfecting

NASA wants to prevent the possibility of contaminating other planets or items in space with microbes from Earth. Which of the following would best be used to sterilize spacecraft being sent to space?

ethylene oxide *** Ethylene oxide is frequently used as a gaseous sterilizing agent in hospitals and dental offices, and NASA uses the gas to sterilize spacecraft designed to land on other worlds lest they accidentally export earthly microbes.

Which of the following could be used to sterilize a heat-sensitive liquid?

filtration *** Filtration is the passage of a fluid (either a liquid or a gas) through a sieve designed to trap particles—in this case, cells or viruses—and separate them from the fluid. It is safe for heat-sensitive liquids.

Aseptic means

free of pathogens.

Fomites are

inanimate objects involved in the indirect contact transmission of pathogens.

The mechanism of action of the antibiotic vancomycin is

inhibition of cell wall synthesis.

Which of the following is NOT an example of symbiosis?

microbes crossing the placenta to the fetus

How does resistance to drugs spread in bacterial populations?

Horizontal gene transfer between bacteria spreads R (resistance) plasmids.

Caleb Bakersfield, a 42-year-old real estate agent, had just returned from a vacation to Russia. His childhood had been rough because of an alcoholic and abusive father, and Caleb had started his own drug addiction in his early teens. By his early twenties, he was addicted to heroin, lived on the streets, and frequently used dirty needles. In his thirties, Caleb joined a program to beat his addiction and to turn his life around. The trip to Russia was to celebrate a decade of being clean. Less than two months after his trip, Caleb started having respiratory complications, including a frequent cough and shortness of breath. He figured it was most likely a respiratory infection and made an appointment with his physician. After listening to Caleb's lungs, Dr. Bell determines that Caleb most likely has a lower respiratory infection and prescribes the antibiotic azithromycin. Dr. Bell reminds Caleb that it is important to complete his entire course of antibiotics, even if he feels better before he finishes all of the medicine. Dr. Bell also collects a sputum sample (mucus coughed up from the lower respiratory tract) and sends it to the laboratory for evaluation. PART A Why does the physician start Caleb on the antibiotic azithromycin before laboratory results come back? PART B Which of the following choices correctly matches the class of antibiotic and its mode of action? The azithromycin does not clear Caleb's respiratory infection. In fact, his cough is getting worse, and on several occasions his sputum has contained blood. Caleb schedules another appointment with Dr. Bell. This time, the two thoroughly discuss his recent travel to Russia, his medical history, and his time spent as an IV (intravenous) drug user. Dr. Bell requests that Caleb provide samples of sputum and blood and that he undergo a tuberculin skin test. Image A shows what Caleb's sputum sample looks like on the microscope. Dr. Bell confirms his diagnosis of tuberculosis using an X-ray image of Caleb's lungs and a rapid diagnostic test (Xpert MTB/RIF), which uses automated PCR to detect M. tuberculosis in 90 minutes. Dr. Bell also receives the results of Caleb's blood test, which confirms that he is also infected with HIV, most likely contracted from a dirty needle. The HIV has weakened Caleb's immune system, rendering it unable to fight off the M. tuberculosis pathogen. His X-ray film shows the presence of a walled-off lesion of bacterial cells (a tubercle) in the lungs. Dr. Bell meets with Caleb to discuss treatment options for his infections. Given that he is infected with HIV, treatment for the tuberculosis is imperative but depends greatly on the susceptibility of the M. tuberculosis to the available antibiotics. Dr. Bell also starts Caleb on HIV therapy. PART C If Caleb's strain of M. tuberculosis is sensitive to antibiotic treatment, which of the following could be used to treat his infection? PART D Why does Dr. Bell start Caleb on HIV therapy in addition to the antibiotics used to treat the tuberculosis? PART E Which of the following contribute to drug resistance in M. tuberculosis?

PART A - Antibiotic therapy is started with a broad-spectrum antibiotic because broad-spectrum antibiotics are effective against many gram-positive and many gram-negative bacteria. *** Azithromycin is a semisynthetic broad-spectrum antibiotic that can be used as an alternative to penicillin, is broader in range than erythromycin, and has better tissue penetration. Dr. Bell most likely assumes that the bacterium causing Caleb's infection will be susceptible to azithromycin and that this drug should clear the infection. PART B - Aminoglycosides and tetracyclines are inhibitors of protein synthesis. - Sulfonamides inhibit the synthesis of essential metabolites. *** Antibacterial drugs are often categorized by their mode of action against the target microbe. The following make up a short list of antibacterial drugs that are commonly used to treat infections. Penicillins (natural and semisynthetic) and cephalosporins are commonly used to inhibit synthesis of the cell wall. Chloramphenicol, aminoglycosides, tetracyclines, and macrolides are common inhibitors of protein synthesis. Polymyxin B and lipopeptides cause damage to the plasma membrane. Rifamycins and quinolones inhibit nucleic acid synthesis. Sulfonamides inhibit metabolic pathways. Combinations of these drugs can also be used to increase efficacy. PART C - streptomycin - isoniazid and ethambutol - rifampin *** Treatment of susceptible strains of M. tuberculosis typically includes a 6-month regimen of isoniazid, ethambutol, pyrasinamide, and rifampin. These are considered first-line drugs for the treatment of tuberculosis. If resistance develops, second-line alternatives, such as aminoglycosides, fluoroquinolones, and para-aminosalicylic acid (PAS) can be added to the regimen. In resistant strains, treatment is more difficult. PART D - Dr. Bell prescribes Caleb HIV therapy because the virus is not affected by the antibiotics used to treat tuberculosis. *** HIV infections are caused by the human immunodeficiency virus, a RNA virus. Viruses are not susceptible to antibiotics; thus the treatment for Caleb's tuberculosis would be effective only against the bacterium, M. tuberculosis. Dr. Bell prescribes the HIV therapy and the antibiotics in order to help Caleb's immune system battle both infections. HIV therapy includes the use of antiretroviral drugs, nucleoside analogs, and nucleotide analogs such as HAART, zidovudine, and tenofovir, respectively. Newer HIV drugs are being created to inhibit viral entry into the cell and to prevent integration of the genome into host DNA. Often, HIV-infected individuals are given a "cocktail" of medications to treat the infection and to help combat antiviral resistance. PART E - Many individuals fail to complete their entire regimen of antibiotics. - Some physicians prescribe the wrong medication, the wrong dosage, or the wrong length of time for treating tuberculosis. - In many areas, tuberculosis antibiotics are unavailable or of poor quality. *** One of the major reasons for drug resistance in M. tuberculosis is the length of antibiotic treatment. It is hard enough to get people to completely finish a course of antibiotics that lasts 7 to 10 days, let alone one that lasts 6 months. Individuals who begin treatment but do not finish only contribute to the resistance problem because the organisms they are harboring and transmitting to others are the ones resistant to treatment. Other factors that contribute to resistance include improper diagnosis and treatment, lack of drug availability, and poor quality of the antibiotics. With the increase in the number of organisms exhibiting resistance, researchers are now developing newer antimicrobials and revisiting ideas from before the antibiotic era.

PART A A patient has been diagnosed with a disease caused by a drug-resistant strain of bacteria. What is a likely way that the bacterium initially acquired resistance? PART B A patient is infected with a bacterium that produces the enzyme beta-lactamase; this enzyme PART C Which of the following does not spread drug resistance throughout a population of bacteria? PART D A particular drug works by interfering with cellular metabolism in Gram-negative bacteria. How might these bacteria become resistant in a way that Gram-positive bacteria never could?

PART A - Mutation *** Genetic mutations can change the phenotype of a cell, which might confer resistance to a particular drug. PART B - inactivates penicillins, carbapenems, and cephalosporins. *** Beta-lactamase destroys the beta-lactam ring of penicillins, carbapenems, and cephalosporins; the functional part of these drugs is a beta-lactam ring. PART C - Efflux pumps *** Efflux pumps can remove a drug from a cell, but do not spread resistance from one cell to another. PART D - Alter porin proteins in the cell's outer membrane *** Altered porin proteins might prevent a drug from entering a cell; Gram-positive bacteria do not have outer membranes or porin proteins.

PART A Prokaryotes contain _____ ribosomes. PART B Antimicrobial drugs are selectively toxic. This means _____. PART C The tRNA molecule holding a growing polypeptide chain is at the _____. PART D Which category of antimicrobial drug works by changing the shape of a ribosome? PART E Which category of antimicrobial drug essentially acts to stall a ribosome as it reads mRNA? PART F Chloramphenicol blocks the action of the large (50S) subunit. This essentially _____. PART G Which antimicrobial drugs affect the structure of the ribosome itself? PART H Which category of drug is complementary to mRNA of the pathogen?

PART A - 70s *** 70S ribosome of prokaryotes is composed of smaller 50S and 30S subunits. PART B - the drugs are more toxic to the pathogens than to the patient *** They selectively target physiological and anatomical differences between pathogens and patients. PART C - P site *** P sites hold developing polypeptide chains. PART D - aminoglycosides *** An aminoglycoside changes the shape of a 30S subunit causing the ribosome to misread the mRNA. PART E - macrolides *** Macrolides block the movement of a ribosome along mRNA, so the E site is never emptied and polypeptide formation is stopped. PART F - prevents the formation of peptide bonds *** Without the formation of peptide bonds, amino acids diffuse away and protein synthesis ceases. PART G - aminoglycosides, antisense nucleic acids, and oxazolidinones *** Each of these drugs actually modifies or prevents the formation of the complete 70S ribosome. PART H - antisense nucleic acids *** The antisense nucleic acids are composed of the same nucleotide bases and are complementary to the mRNA.

PART A Transposons are stretches of DNA hundreds to thousands of nucleotide bases long. If a transposon were inserted into the middle of a gene, what kind of mutation would it be? PART B A portion of a gene has the nucleotide sequence: GCA UAU ACG CAA. If there is a point mutation in the second of these codons to: GCA UAG ACG CAA, what would be the effect on amino acid sequence? PART C A scientist discovers a mutation resulting from a single nucleotide base pair being removed from the DNA of a gene. The change in DNA sequence is known as PART D A portion of a gene has the nucleotide sequence: GGG AGG UUU ACA; a mutation occurs to change the sequence to AGG AGG UUU ACA. Such a change in DNA is known as a

PART A - Gross mutation *** Gross mutations are large deletions or insertions, such as the insertion of a transposon. PART B - Nonsense mutation *** A nonsense mutation is a point mutation that changes an amino acid codon into a stop codon; in this example, the codon UAU, which codes for tyrosine, is changed to the stop codon, UAG. PART C - a frameshift mutation. *** A frameshift mutation results from an insertion or deletion that changes all subsequent codons. PART D - substitution mutation. *** A substitution mutation involves a change from one DNA base to another; in this case, G was changed to A.

Sarah might have been 85 years old, but her mind was still sharp; it was her body that was failing. After she broke her hip by falling in the bathroom, she had succumbed to a series of complications that ultimately required admittance to a large university-associated hospital in New York City. Treatment necessitated a urinary catheter, a feeding tube, and intensive antibiotic therapy. While hospitalized, she acquired a life-threatening urinary tract infection of multi-drug-resistant (MDR) Enterococcus faecium. Enterococci are normal members of the microbiota of the colon, yet these Gram-positive bacteria have a propensity to acquire genes that convey resistance to antimicrobial drugs. As a result of such horizontal gene transfer, E. faecium has become an MDR bacterium—a strain resistant to many different kinds of antimicrobials. Drug-resistant enterococci are a leading cause of nosocomial infection. Physicians treated Sarah with a series of antimicrobial drugs, including metronidazole, penicillin, erythromycin, ciprofloxacin, and vancomycin, but to no avail. After 90 days of hospitalization, she died. PART A What is a nosocomial infection? PART B What term is used to describe bacterial cells that can naturally take up DNA from their environment? PART C How can hospital personnel prevent the spread of resistant E. faecium throughout the hospital? PART D Which of the following is NOT used by bacteria to acquire new genetic material? PART E What does MDR mean?

PART A - This is a hospital-acquired infection. *** Patients acquire the infection during their hospital stay. PART B - competent cells *** Competent cells can pick up DNA from the environment and incorporate it into their genome. PART C - Hospital personnel should wash their hands when entering and leaving a patient's room. ***Hand washing is one of the best means to prevent the spread of disease. PART D - crossing over *** Crossing over is used by eukaryotic cells during meiosis to increase genetic diversity. PART E - multi-drug-resistant *** multi-drug-resistant

PART A An exotoxin that has the ability to kill or damage host cells is referred to as a(n) PART B Which domain of the A-B toxin binds to cell surface receptors on the host cell? PART C How are superantigens different from other types of exotoxins? PART D A person who attended a picnic early in the day develops a very high fever and is unresponsive by the evening. This person most likely has been exposed to a(n) PART E A patient who has been hospitalized with uncontrolled muscle spasms has probably been infected with bacteria that secrete a(n)

PART A cytotoxin. PART B B domain PART C Superantigens cause an overstimulation of the host immune system. PART D superantigen. PART E neurotoxin.

PART A Jerica takes her young son to the pediatrician for regular childhood immunizations. While there, they wait in a room full of sneezing, sniffling, coughing youngsters. Despite making sure that her son stays at least six feet (two meters) from the other children and doesn't touch any play toys in the waiting room, microbes could still spread to her son by PART B An example of a mechanical vector is: PART C A patient is sickened after being infected with Escherichia coli (E. coli) from consuming contaminated lettuce; this is a type of _______________ disease transmisson. PART D A patient with West Nile viral encephalitis asks his nurse practitioner how he could have contracted the disease. The NP explains that the causative virus is carried by infected mosquitoes from birds to people. This is an example of disease transmission through

PART A - vehicle transmission. *** Vehicle transmission is the spread of pathogens via air, drinking water, or food or by handling bodily fuids outside the body, such as in a medical facility. PART B - a housefly at a picnic. *** Mechanical vectors are arthropods that carry pathogens without being a host themselves. PART C - vehicle *** Vehicle transmission is the spread of pathogens via air, drinking water, or food or by handling bodily fluids outside the body. PART D - a biological vector. *** Biological vecors are arthropods that carry pathogens and also serve as hosts for the pathogen.

PART A What is the inducer molecule in the lac operon? PART B With which genetic region does the repressor protein interact? PART C When the cell is not in the presence of lactose, PART D What is the basic function of the lac operon? PART E According to the animation, to what genetic element does the RNA polymerase bind?

PART A Allolactose PART B The operator region PART C the repressor proteins bind to the operator. PART D To code for enzymes involved in catabolizing lactose. PART E The promoter

PART A Bacterial conjugation is often referred to as bacterial sex. Why is this term inaccurate? PART B What must occur for bacterial conjugation to take place? PART C Which statement about conjugation is false? PART D Based on the animation, what is transferred during bacterial conjugation?

PART A Conjugation does not result in the formation of new offspring. PART B The cells must come into contact with each other. PART C Conjugation is a process of bacterial reproduction. PART D A bacterial plasmid

PART A What characteristic of DNA allows two connected DNA polymerases to synthesize both the leading and lagging strands? PART B What is the function of the connector proteins? PART C Which DNA strand is synthesized continuously? PART D Which of the following are terms associated with Okazaki fragments? PART E Why is the DNA synthesis of the lagging strand considered discontinuous?

PART A DNA is flexible PART B They link the leading strand DNA polymerase and the lagging strand DNA polymerase together. PART C Leading strand PART D Lagging strand, DNA ligase, and discontinuous PART E The synthesis is moving in the opposite direction from the replication fork.

In 1924, Dr. Curtis Welch was the town physician in Nome, Alaska. At the time, Nome was the northwestern most city in North America and during the winter months, it was icebound—shut off from the rest of the world. As the last supply ship left town, Dr. Welch was examining an Eskimo child suspected of having tonsillitis. He had no idea of the drama that was unfolding before him. By the next morning, the Eskimo girl had died. Dr. Welch was concerned; although possible, it was rare for someone to die from tonsillitis. In January of 1925, Dr. Welch's concerns were validated when he examined a boy in the hospital. The boy had swollen glands, fatigue, and a fever. More importantly, the boy had thick, gray lesions on his throat and nasal membranes. There is a photo of the human mouth opened with a pseudomembrane shown. These gray lesions are known as a psuedomembrane, and are characteristic of infection by Corynebacterium diphtheriae, the causative agent of diphtheria. Diphtheria is a highly contagious infection spread by respiratory secretions or via droplets in the air, such as those released during coughing or sneezing. Dr. Welch knew that the infection could very quickly spread among the residents of Nome. Worse yet, Dr. Welch's supply of antitoxin, which is needed to treat the infection, was not only expired but was only sufficient enough to treat about six patients. PART A During infection, C. diphtheriae grows and multiplies within the upper respiratory tract. As each bacterial cell prepares for division the chromosome must be replicated so that each daughter cell receives a copy of the genetic information. The following statements summarize the major steps in replicating the bacterial chromosome. Arrange the statements in the correct order to describe the process of replication of the leading strand. Place the following statements in the correct order of events for replication of the leading strand. Dr. Welch contacted the governor of Alaska and the United States Public Health Service to try to find a source of antitoxin. The town was put under quarantine to try to control the outbreak. PART B During infection, C. diphtheriae expresses a variety of genes that are used to establish infection and cause disease. One of these genes encodes for diphtheria toxin. Expression of the toxin requires the genetic information contained in DNA be converted into protein. The 1st step in this process is transcription, in which DNA is converted into mRNA. The following is a short piece of the DNA sequence for diphtheria toxin (written 5' to 3'): TAA GCG TAG AAC TTG. Which of the following sequences represents the mRNA (written 5' to 3') that will be generated from this template DNA sequence? A supply of antitoxin was discovered at Anchorage Railroad Hospital. The challenge was how to get the antitoxin to Nome. Air travel was extremely limited; bush pilots were just beginning to explore remote areas of Alaska. Much transport was done by train, but the nearest station was in Nenana, about 675 miles from Nome. It was decided that the most effective and efficient way to get the antitoxin to Nome was via a dog sled relay. PART C The major virulence factor produced by C. diphtheriae is diphtheria toxin. The production of diphtheria toxin during infection is controlled by a repressor, DtxR. The activity of DtxR is regulated by iron, which acts as a corepressor. During an infection, the levels of iron available in the tissues for use by C. diphtheriae are low. What effect will the decreased iron availability have on the production of diphtheria toxin PART D Diphtheria toxin kills eukaryotic cells by affecting translation. More specifically, the toxin prevents movement of tRNAs from the A site to the P site of the ribosome. Predict what the result(s) of this inhibition would be. Over the next 5 ½ days, a relay involving 20 mushers and about 150 sled dogs traveled to deliver the antitoxin to Nome. The conditions were absolutely brutal—the wind chill pushed the temperature as low as -85 degrees Farenheit. Several mushers suffered frostbite, and several dogs died as a result of the harsh travel. PART E The ability of C. diphtheriae to produce toxin is acquired via the process of specialized transduction. This is just one of the mechanisms that bacteria use to transfer genetic material to other bacteria, a process known as horizontal gene transfer. There are different mechanisms for horizontal gene transfer in bacteria, each with its own unique features. For each of the following phrases, indicate whether it occurs during transformation, conjugation, generalized transduction, or specialized transduction by dragging it to the appropriate bin.

PART A FIRST TO LAST EVENT - Double stranded DNAis unwound by helicase. - Proteins bind to the DNAin order to stabilizethe single strands. - Primase synthesizesan RNA primer. - DNA polymerase catalyzesformation of a sugar-phosphatebond between neighboringnucleotides. - Hydrogen bondsform between thecomplementary bases. *** The process of replicating the leading strand is fairly straightforward—helicase unwinds the strands, primase makes a primer, and DNA polymerase synthesizes the new strand of DNA. Remember that during replication both strands will be used as templates—the other strand is known as the lagging strand and is synthesized in a discontinuous manner as polymerase can only synthesize in a 5' to 3' direction. The lagging strand is synthesized in short fragments (Okazaki fragments) that will ultimately be joined together via the action of a 2nd DNA polymerase and DNA ligase. PART B - CAA GUU CUA CGC UUA *** This sequence represents the corresponding mRNA written 5' to 3'. All thymine residues have been replaced with uracil, a characteristic of all RNA. PART C - The lack of corepressor binding to DtxR will lead to a loss of repression and an increase in the production of toxin. *** The decreased level of iron results in lack of corepressor binding to DtxR. Without corepressor binding, DtxR will be unable to bind to the operator and repress transcription of the diphtheria toxin gene. This will result in a greater amount of toxin production, as transcription is no longer being repressed. PART D - New tRNAs will not be able to enter the ribosome. - Protein synthesis will be interrupted because the peptide chain is inhibited from growing. *** In order for protein synthesis to occur, the polypeptide chain must elongate. Elongation is dependent on the movement of tRNAs from the A to the P to the E site. During infection, the toxin that is produced by C. diphtheriae will block the A site. This effectively shuts down the ability of the ribosome to function. If the cell is unable to synthesize proteins, it will not survive. PART E TRANSFORMATION - Requires the recipient cell to be competent. - Naked DNA is transferred from donor to recipient. CONJUGATION - Donor and recipient cells must be of an opposite mating type. - Requires direct contact between bacterial cells, which is typically mediated by a sex pilus. GENERALIZED TRANSDUCTION - A phage infects the bacterial cell, thereby transferring bacterial, plasmid, and/or viral DNA to the recipient. SPECIALIZED TRANSDUCTION - During phage infection, particular bacterial genes are transferred to the recipient. *** The last dog sled team delivered the antitoxin to Nome on February 2, 1925, and the antitoxin was quickly distributed. A 2nd shipment of antitoxin arrived a couple of weeks later, again by dog sled. Although it is estimated that only eight people died as a result of the outbreak, Dr. Welch believed that the number was probably greater than 100 due to the fact that many Eskimo likely did not report their dead. The delivery of the antitoxin to Nome in 1925 was an amazing feat; each year it is commemorated by the Iditarod Trail Sled Dog Race®. Today, there are fewer than five reported cases of diphtheria in the United States each year. This is due to the immunization that most children receive as part of their usual immunization panel. The DTaP vaccine ("D" for diphtheria) contains an inactive form of the toxin that causes the body to make antibodies against diphtheria, thereby protecting against C. diphtheriae infection.

Changes in genetic sequences, or mutations, can result from various types of damage. The damage may be minor to extensive alterations in the DNA. Correspondingly, mutations may result in no phenotypic change or in phenotypic changes ranging from minor with little impact on fitness to severe enough to destroy a gene product and compromise an organism's ability to survive. Point mutations are those that alter a single base pair or base location, and include substitutions and frameshift mutations. They can range in severity from no phenotypic change to complete loss of function. PART A Rank the following point mutations in order of least damaging to most damaging if they occur in the middle of the coding sequence of a polypeptide PART B Not all changes in amino acid sequence are deleterious, some may even be beneficial. Which of the following point mutations is most likely to alter a protein product without destroying its function? PART C Which of the following will most likely contribute to the spread of a genetic mutation among bacterial species? Genetic Mutation, Gene Transfer and Their Contribution to Antibiotic Resistance The use of antibiotics to treat infections has been accompanied by an increase in antibiotic resistance in populations of medically important bacteria. The development and spread of antibiotic resistance is an area of increasing concern with long term implications for treatment of infectious diseases. PART D Which of the following statements is MOST correct regarding the development of antibiotic resistance in populations of bacteria? PART E A common mechanism for antibiotic resistance is alteration of the molecule targeted by the antibiotic. Very small changes in the structure to extensive alterations may produce a gene product on which the antibiotic has limited effect. Match the type of point mutation with the type of damage it is most likely to produce. PART F Rank the following events in order from GREATEST to LEAST contribution to the spread of antibiotic resistance in bacterial populations.

PART A LEAST TO MOST DAMAGING Silent Missense Frameshift Nonsense PART B - Missense *** Changes in gene sequences that alter function without destroying the function of a polypeptide may become permanent in the genome of the organism. PART C - transformation *** Some mutations produce small changes in phenotype which may persist and spread in the absence of strong selective pressure. Similarly, some changes in phenotype may confer an advantage under certain conditions. PART D - Exposure to antibiotics selects for the members of a bacterial population which already have a resistant phenotype. *** The appearance of bacteria resistant to antibiotics is the result of natural selection acting on populations of bacteria which include a number of genetic variants. PART E - Missense: Small change in gene product which may or may not alter function. - Nonsense: Premature termination of gene product with probable loss of function. - Frameshift: Extensive change in gene product structure and function. - Silent: No change in gene product. *** Both frameshift and nonsense mutations are likely to produce proteins that do not function or function aberrantly, while missense mutations generally produce small changes. Depending on their location in a polypeptide, missense mutations may have no effect to significant effect on function, and are unlikely to result in major changes in the structure of a polypeptide. PART F Great to Least contribution - horizontal transfer - vertical transfer - new mutations *** Cells with mutations that result in small alterations of function without complete loss of function often are at a disadvantage compared to wild-type cells, and therefore have a lower rate of reproduction. If resistance genes are only introduced into a population by the reproduction of these disadvantaged cells, the frequency will increase relatively slowly. Horizontal transfer distributes new genes widely in populations of related bacteria.

PART A As shown in the animation, the start codon also codes for which amino acid? PART B How many codons code for the amino acid arginine? PART C GAU codes for PART D Which of the following amino acids is coded by only one codon? PART E What would happen if the mRNA codon that coded for Cys was mutated in the third position from a U to an A?

PART A Methionine PART B Six PART C aspartic acid PART D Trp PART E A stop codon would be introduced prematurely.

PART A What are leukocidins? PART B Measles viruses are capable of inactivating host defenses by PART C Meningitis and gonorrhea are caused by PART D How do superantigens enable pathogens to hide from the immune system if they actually stimulate the immune system? PART E How can capsules enable bacteria to evade the immune system?

PART A Molecules that are capable of destroying phagocytes PART B suppressing the immune system. PART C Neisseria species. PART D They cause the immune system to produce an exaggerated response, distracting it from the actual pathogen. PART E Capsules block the complement biding sites on the surface of the pathogen.

PART A When the cell is NOT in the presence of tryptophan, PART B When is the repressor protein transcribed? PART C Why is the tryptophan operon turned off in the presence of tryptophan? PART D What is the overall function of the trp operon? PART E According to the animation, how do the repressor proteins block the transcription of the structural genes?

PART A RNA polymerase can transcribe mRNA. PART B It is always transcribed. PART C Tryptophan binds to and activates the repressor proteins; the repressor proteins, in turn, bind to the operator, preventing transcription. PART D To ensure that the cell has a supply of tryptophan at all times PART E It binds to the operator when activated.

PART A How are immune cells able to detect foreign pathogens? PART B How does a capsule help certain bacteria evade detection by the immune system? PART C Which of the following microorganisms actually grows inside the macrophage? PART D How does the protozoan Trypanosoma evade detection by the immune system?

PART A They are able to detect structures on the surfaces of foreign cells that are not found in the host. PART B The capsule is composed of polysaccharides that are similar to those found in the host; thus, the immune system does not recognize it as foreign. PART C Tuberculosis bacterium PART D It can change the surface antigens frequently, preventing the immune system from tracking it.

***** During the fall of 2012, a multi-state outbreak of meningitis occurred. The source of the infection was traced to contaminated methylprednisolone acetate, a steroid commonly used to treat back pain. Each of the infected people had received an injection of the steroid contaminated with the fungus Exserohilum rostratum. While the investigation is still pending, one current area of focus is the quality-assurance practices of the company responsible for manufacture of the drug. Quality assurance (QA) refers to the examination of the process of manufacturing a drug. QA practices are governed by both federal and local agencies, and they help to ensure that manufacturing practices for products such as drugs guarantee both efficacy and safety of the product. Quality control (QC) is an aspect of QA that focuses on the end-product of the process. During the production of a drug, one facet of a QC technician's job is to evaluate microbiological safety during the production process. As you answer the following questions, imagine that you are working as a QC technician at a pharmaceutical company. Part A During production of a drug, all work area surfaces must be disinfected using sterilized disinfectants. Which of the following statements about disinfectants are true? Part B Assume that you have an antimicrobial agent specific for each of the targets listed below. Indicate which type of microbe would be most susceptible to the agent by placing it in the appropriate bin. Part C At each stage of production, sterility of the preparation is a major consideration. When considering appropriate measures to implement to control microbial growth, one must think about the susceptibility of possible microbial contaminants. Apply your knowledge of the structural features of microbes and the mechanisms of action for antimicrobial agents to rank the following microbes according to their susceptibility. Part D The preferred method of sterilization during drug production is heat. Heat sterilization can occur in two forms: moist or dry. Autoclaving is the most commonly used application of moist heat for sterilization. Which of the following statements about autoclaving is true? Part E One alternative to autoclaving for sterilization of liquids is filtration. Imagine that you are using a filter to sterilize a drug solution. You use a filter with a 0.22 μmμm pore size. Which of the following microbes will effectively be removed by this filter?

Part A - Endospores and viruses can resist disinfectant treatment. - Disinfection can occur by physical or chemical means. - Disinfectants are used to inhibit or destroy pathogens. *** During production of a drug, all work surfaces must be disinfected to inhibit the growth of microbes. From a practical standpoint, sterilization (elimination of all microbes) of all work surfaces (e.g., benches, floors, chairs, equipment) is not feasible. Part B ALL BACTERIA - glycolytic enzymes - membrane proteins GRAM- POSITIVE BACTERIA - peptidoglycan GRAM-NEGATIVE BACTERIA -None VIRUS - envelope proteins ALL BACTERIA AND VIRUS nucleic acids *** As you consider which microbes could possibly contaminate work surfaces, it is important for you to understand antimicrobial targets. This information is essential for you to make the most appropriate choice in a given environment. Part C LEAST TO MOST SUSCEPTIBLE - prions - endospores - Gram-negative bacteria - Gram-positive bacteria - enveloped virus *** Microbial structure plays an important role in susceptibility to antimicrobials. While you might think that a viral envelope would confer protection, it is more easily broken down than a protein coat. Gram-positive bacteria tend to be more susceptible to agents that attack the cell wall (recall that they lack an outer membrane). Bacterial endospores are designed to withstand extreme stress; this also means that they are more difficult to eliminate compared to bacterial cells. Prions remain the most resistant of all; however, recently, an enzyme has been shown to be effective in eliminating prion contamination on medical instruments. Part D The effectiveness of an autoclave is dependent on an increase in pressure and corresponding increase in temperature. *** Autoclaving can be used to effectively and efficiently sterilize a variety of items used in the production of a drug. During autoclaving, the steam must contact all items or liquids. This is why items should be wrapped in porous materials rather than foil and liquids need to have loose caps. Although effective, sometimes autoclaving cannot be used for liquid sterilization (e.g., sterilizing a solution with heat-labile components). Part E - bacteria such as E.coli - fungi - yeast *** The use of membrane filters offers an effective alternative to autoclaving for the sterilization of liquids. It is essential to choose the correct pore size for filtration to ensure that any possible contaminants are trapped by the filter and do not become part of the final solution. Therefore, always choose a filter with a pore size that is significantly smaller than your smallest possible contaminant.