Micro CH 20 – Flashcards
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What is meant by selective toxicity?
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Chemotherapeutic agents should act against the pathogen and not the host.
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Why are chemotherapeutic agents that work on the peptidoglycan cell wall of bacteria a good choice of drug?
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Humans and other animal hosts lack peptidoglycan cell walls.
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Why is polymyxin only used on the skin?
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It can also damage living human cell membranes, but the drug is safely used on the skin, where the outer layers of cells are dead.
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Quinolones and fluoroquinolones act against what bacterial target?
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DNA gyrase
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Why is it difficult to find good chemotherapeutic agents against viruses?
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Viruses depend on the host cell's machinery, so it is hard to find a viral target that would leave the host cell unaffected.
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In the table, as illustrated by the data shown, the minimal bactericidal concentration of antibiotic X is
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15 μg/ml.
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Which of the following methods of action would be bacteriostatic?
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inhibition of protein synthesis
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In the presence of penicillin, a cell dies because
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it undergoes lysis.
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The antibiotic tetracycline binds to the 30S subunit of the ribosome, as shown by the dark black bar on the right portion of the diagram in the figure. The effect is to
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interfere with the attachment of the tRNA to mRNA-ribosome complex.
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Which of the following antibiotics is recommended for use against gram-negative bacteria?
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polymyxin
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Niclosamide prevents ATP generation in mitochondria. You would expect this drug to be effective against
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helminths.
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Which of the following is an antiprotozoan drug that interferes with anaerobic metabolism?
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metronidazole
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Penicillin was considered a "miracle drug" for all of the following reasons EXCEPT
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it was the first antibiotic.
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More than half of our antibiotics are
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produced by bacteria.
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Which of the following is mismatched?
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Florey and Chain identification of Penicillium as the producer of penicillin
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T/F Only microbes produce antimicrobial peptides.
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False
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Most of the available antimicrobial agents are effective against
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ONLY bacteria.
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The antimicrobial drugs with the broadest spectrum of activity are
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tetracyclines.
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Protozoan and helminthic diseases are difficult to treat because
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their cells are structurally and functionally similar to human cells.
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Why is it more difficult to treat viral infections than it is to treat bacterial infections?
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Viruses use the host cell's processes to carry out their own reproduction.
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T/F An antibiotic that attacks the LPS layer would be expected to have a narrow spectrum of activity.
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True
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Antimicrobial peptides (AMPs) frequently work by
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disrupting the plasma membrane.
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Which of the following statements about drugs that competitively inhibit DNA polymerase or RNA polymerase is FALSE?
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They cause cellular plasmolysis.
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The antibiotic actinomycin D binds between adjacent G-C pairs, thus interfering with
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transcription.
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More than half of the antibiotics used today are produced by __________.
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Streptomyces species
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Sulfanilamides interfere with __________.
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folic acid synthesis in bacteria
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T/F Both trimethoprim and sulfamethoxazole inhibit reactions along the same metabolic pathway.
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True
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A drug that inhibits mitosis, such as griseofulvin, would be more effective against
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fungi.
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The antibiotic chloramphenicol binds to the 50S subunit of the ribosome, as shown in the figure. The effect is to
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prevent peptide bond formation in prokaryotes.
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Which of the following antimicrobial agents has the fewest side effects?
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penicillin
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Which of the following antibiotics does NOT interfere with cell wall synthesis?
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macrolides
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Which of the following statements is FALSE?
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Interferon inhibits glycolysis.
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Which of the following organisms would MOST likely be sensitive to natural penicillin?
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Streptococcus pyogenes
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Which of the following would be selective against the tubercle bacillus?
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ethambutol inhibits mycolic acid synthesis
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Which of the following antimicrobial agents is recommended for use against fungal infections?
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amphotericin B
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The structures of the influenza drug Tamiflu and sialic acid, the substrate for influenza virus's neuramidase, are shown in the figure. What is the method of action of Tamiflu?
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competitive inhibition
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Which of the following does NOT affect eukaryotic cells?
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semisynthetic penicillins
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Mebendazole is used to treat cestode infections. It interferes with microtubule formation; therefore, it would NOT affect
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bacteria.
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If penicillin G is chosen as the best treatment for a given infection, what microorganisms are most likely the cause?
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gram-positive bacteria
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How do antifungal drugs such as miconazole and amphotericin B function?
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by disrupting the plasma membrane
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T/F Antiviral drugs target viral processes that occur during viral infection.
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True
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T/F Phage therapy has been used in the past as an antiviral treatment.
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False
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Which statement regarding tests for microbial susceptibility to chemotherapeutic agents is FALSE?
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The Kirby-Bauer test is useful because it can differentiate bacteriostatic effects from bactericidal effects.
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Which of the following statements about drug resistance is FALSE?
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It is found only in gram-negative bacteria.
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Drug resistance occurs
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when antibiotics are used indiscriminately.
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Use of antibiotics in animal feed leads to antibiotic-resistant bacteria because
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the antibiotics kill susceptible bacteria, but the few that are naturally resistant live and reproduce, and their progeny repopulate the host animal.
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Why is methicillin-resistant Staphylococcus aureus (MRSA) methicillin resistant?
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It produces a modified version of the molecule that is targeted by the drug.
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T/F Community-acquired MRSA is typically more virulent than health care-associated MRSA.
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True
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Certain cancer cells have ABC transport molecules at the cell surface. These transporters use energy from ATP to move chemotherapeutic agents out of the cell. Which of the following do you think these transporters are most closely related to?
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membrane pumps
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A researcher creates an antibiotic that binds to a protein present only on B. anthracis (the causative agent of anthrax), lysing the cell from the outside. After a couple of years using this antibiotic, some resistant organisms are found. Which of the following best outlines the mechanism for development of this resistance?
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mutation in B. anthracis → altered target → resistant bacterium
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A new bacterial molecule is discovered. This molecule binds to an antibiotic and facilitates the binding of a phosphate group, thus inactivating the antibiotic. Which category best describes the mechanism of antibiotic resistance conferred by this molecule?
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bacterial enzymes
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Which of the following does NOT constitute an advantage of using two antibiotics together?
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Two are always twice as effective as one.
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Consider a Kirby-Bauer disk-diffusion assay. If you put penicillin and streptomycin disks adjacent to one another, the zone of inhibition is greater than that obtained by either disk alone. This is an example of __________.
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synergism
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Which antibiotic is overcome by beta-lactamases?
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Penicillin
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How might efflux pumps increase antibiotic resistance in bacteria?
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Resistant bacteria can have more efflux pumps, and can have less specific efflux pumps.
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Bacteria that are resistant to sulfonamide have enzymes that have a greater affinity for what?
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PABA
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Why would an efflux pump for penicillin located on a bacterial cell membrane not be effective at providing resistance to the drug?
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Penicillin disrupts the cell wall, which is located outside of the cell membrane.
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Membrane transport proteins are required for which mode(s) of antibiotic resistance?
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Efflux pumps, beta-lactamases, and modification of porins all utilize membrane transport proteins.
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What is meant when a bacterium is said to become "resistant" to an antibiotic?
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The bacterium is neither killed nor inhibited by the antibiotic.
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When a patient is treated with antibiotics, __________.
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the drug will kill or inhibit the growth of all of the sensitive bacterial cells
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The process of acquiring antibiotic resistance by means of bacteriophage activity is called
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transduction.
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Which of the following mutations would not result in antibiotic resistance?
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Silent mutation
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R-plasmids are most likely acquired via
(check all that apply)
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bacterial conjugation.
