Chapter 20 mastering

You have a 200 mg/ml antibiotic solution. You prepare serial dilutions (1:2, 1:4, etc.) of the antibiotic; the first tube contains 100 mg/ml. You then inoculate each tube with Salmonella. Bacteria grow in tubes 4, 5, and 6. You subculture bacteria from tubes 1 through 3 to nutrient broth. Growth occurs in the tube 3 subculture. You can conclude that the MIC is __________. 25 mg/ml 12.5 mg/ml 50 mg/ml 200 mg/ml None of the listed choices

25 mg/ml

Which of the following are common targets for bacterial resistance to antibiotics? Blocking the drug's entry into the cell Inactivation of the drug by enzymes Alteration of the drug's target site All are common targets for bacterial resistance to antibiotics.

All are common targets for bacterial resistance to antibiotics.

__________are substances that inhibit other microorganisms and are produced by bacteria and fungi.

Antibiotics

Bacterial infections are easier to treat using chemotherapy than are other types of infections caused by other types of microorganisms. Why? Bacteria are prokaryotic. Bacteria are more sensitive to chemicals. Bacteria are smaller than the other types of pathogens. Bacteria grow more slowly.

Bacteria are prokaryotic.

Which of the following is NOT a mechanism by which antibiotic resistance spreads horizontally among bacteria? Plasmid transfer Bacterial conjugation Bacterial transcription Transduction

Bacterial transcription

Which of the following types of antibiotics is most likely to be associated with the development of a superinfection? β-lactam antibiotics Bactericidal antibiotics Narrow-spectrum antibiotics Broad-spectrum antibiotics Bacteriostatic antibiotics

Broad-spectrum antibiotics

What is meant by selective toxicity? Chemotherapeutic agents should have only one mode of action. Chemotherapeutic agents should work on many different targets on a pathogen. Chemotherapeutic agents should work on certain types of pathogens. Chemotherapeutic agents should act against the pathogen and not the host.

Chemotherapeutic agents should act against the pathogen and not the host.

Which drug would be used to treat athlete's foot? Amantadine Polymyxin B Clotrimazole Neomycin Chloroquine

Clotrimazole

Semisynthetic penicillins

Contain chemically added side chains, making them resistant to penicillinases

Quinolones and fluoroquinolones act against what bacterial target? Metabolic pathways unique to bacteria DNA gyrase Bacterial ribosomes Cell walls Cell membranes

DNA gyrase

Membrane transport proteins are required for which mode(s) of antibiotic resistance? Efflux pumps, beta-lactamases, and modification of porins all utilize membrane transport proteins. Efflux pumps Beta-lactamases Modification of a metabolic enzyme Modification of a porins

Efflux pumps, beta-lactamases, and modification of porins all utilize membrane transport proteins.

Which of the following antibiotics is frequently used as an alternative for those who are allergic to penicillin? Vancomycin Ethambutol Amoxicillin Streptomycin Erythromycin

Erythromycin

Why are chemotherapeutic agents that work on the peptidoglycan cell wall of bacteria a good choice of drug? Humans and other animal hosts lack peptidoglycan cell walls. They are less expensive that other chemotherapeutic agents. Bacteria are especially sensitive to these compounds. The drugs also work against DNA gyrase.

Humans and other animal hosts lack peptidoglycan cell walls.

Which drug-resistance mechanism would most likely inactivate penicillin, a drug that targets cell wall synthesis? Inactivation by enzymes Altered cellular uptake of antibiotics Efflux of antibiotics Altered ribosome shape

Inactivation by enzymes

Which of the following mechanisms is antifungal? Inhibit peptidoglycan synthesis Inhibit 70S ribosomes Inhibit ergosterol synthesis Interfere with anaerobic metabolism Cause muscle spasms

Inhibit ergosterol synthesis

What is the method of action of nucleoside analogs? Inhibition of protein synthesis Disruption of plasma membrane Inhibition of DNA synthesis Inhibition of cell wall synthesis

Inhibition of DNA synthesis

Which antimicrobial works by inhibiting the synthesis of mycolic acid? Penicillin Vancomycin Chloramphenicol Isoniazid Methicillin

Isoniazid

What is the benefit of combining penicillins with potassium clavulanate (clavulanic acid)? It makes penicillin more stable in stomach acid. It increases the spectrum of activity. It inhibits penicillinase. It decreases potency of penicillin.

It inhibits penicillinase.

Why is methicillin-resistant Staphylococcus aureus (MRSA) methicillin resistant? The bacteria are able to prevent entry of the drug into the cell. It actively pumps the antibiotic out of the cell. It produces a modified penicillin binding protein (PBP) target molecule that is not effectively inhibited by the drug. It has an enzyme that destroys methicillin

It produces a modified penicillin binding protein (PBP) target molecule that is not effectively inhibited by the drug.

Which of the following is an antihelminthic drug that causes paralysis of the worm? Mebendazole Ivermectin Niclosamide Praziquantel

Ivermectin

The __________ test is a commonly used disk-diffusion method for evaluating antibiotic effectiveness.

Kirby-Bauer

Which of the following statements about antibiotics is true? Penicillin was first discovered by two researchers named Florey and Chain. The finding of antibiotic-producing microorganisms is a rare event. Antibiotics are not typically produced by microorganisms growing in their natural environments. Most of our antibiotics are produced by Streptomyces, a genus of filamentous soil bacteria.

Most of our antibiotics are produced by Streptomyces, a genus of filamentous soil bacteria.

Which of the following is a broad-spectrum, topical antibacterial compound? Bacitracin Polymyxin B Caspofungin Neomycin

Neomycin

Bacteria that are resistant to sulfonamide have enzymes that have a greater affinity for what? PABA Sulfonamide Tetrahyrdrofolic acid Tetracycline

PABA

Which antibiotic is overcome by beta-lactamases? Tetracycline Sulfonamide Penicillin Tetracycline, Penicillin, and Sulfonamide are all affected by beta-lactamase.

Penicillin

Why would an efflux pump for penicillin located on a bacterial cell membrane not be effective at providing resistance to the drug? The efflux pumps would not stop penicillin from blocking metabolic pathways. There are fewer efflux pumps on the cell membrane. The cell membrane is the target of penicillin. Penicillin disrupts the cell wall, which is located outside of the cell membrane.

Penicillin disrupts the cell wall, which is located outside of the cell membrane.

Streptomycin is a broad-spectrum antibiotic that binds to ribosomes. Which bacterial process does streptomycin inhibit? Plasma membrane synthesis Cell wall synthesis Protein synthesis DNA replication

Protein synthesis

How might efflux pumps increase antibiotic resistance in bacteria? Resistant bacteria may have a greater number of efflux pumps on their cell surfaces. Some bacteria can decrease the specificity of their efflux pumps, increasing the number of different antibiotics the pumps can eliminate. Some bacteria can change the chemical structure of the antibiotic. Efflux pumps can never be modified to increase antibiotic resistance. Resistant bacteria can have more efflux pumps, and can have less specific efflux pumps.

Resistant bacteria can have more efflux pumps, and can have less specific efflux pumps.

Which of the following drugs inhibits the synthesis of mRNA in bacteria? Ampicillin Trimethoprim Ethambutol Rifampin Polymyxin B

Rifampin

More than half of the antibiotics used today are produced by __________.

Streptomyces species

Which of the following antibiotics inhibits protein synthesis? Vancomycin Cephalosporin Rifampin Streptomycin Isoniazid

Streptomycin

Which of the following is NOT a reason for the selective toxicity of sulfa drugs? Sulfa drugs inhibit a bacterial enzyme. Sulfa drugs cause production of antimetabolites. Bacteria must synthesize folic acid. Humans get folic acid from their diet; they do not synthesize it.

Sulfa drugs cause production of antimetabolites.

Which statement regarding tests for microbial susceptibility to chemotherapeutic agents is FALSE? During a disk-diffusion test, a clear zone around the test disk indicates that growth was inhibited. The Kirby-Bauer test is useful because it can differentiate bacteriostatic effects from bactericidal effects. A broth dilution test is often used to determine MIC and MBC of an antimicrobial drug. During the Kirby-Bauer test, a Petri plate with agar medium is uniformly inoculated with a standardized amount of a test organism.

The Kirby-Bauer test is useful because it can differentiate bacteriostatic effects from bactericidal effects.

minimum bactericidal concentration (MBC)

The lowest concentration of a chemotherapeutic agent that kills bacteria

While observing the results of a disk-diffusion susceptibility test, you note an enlarged oval zone of inhibition around two adjacent antibiotic disks. Which of the following is the most likely explanation? The two antibiotics are bacteriostatic. The two antibiotics are bactericidal. The two antibiotics are synergistic. The two antibiotics are antagonistic.

The two antibiotics are synergistic.

Which of the following best describes the mode of action of aminoglycosides? They interfere with protein synthesis by changing the shape of the ribosome. They interfere with purine biosynthesis. They disrupt the cell wall. They disrupt the plasma membrane.

They interfere with protein synthesis by changing the shape of the ribosome.

Which of the following statements is true about superinfections? They are caused by endospore-forming bacteria. They inhibit protein synthesis. They may be caused by antibiotic-resistant bacteria. They occur only in people who have immunodeficiencies.

They may be caused by antibiotic-resistant bacteria.

Why is it difficult to find good chemotherapeutic agents against viruses? Viruses infect both bacteria and human cells. There is no effective way to deliver the drug to the virus. Viruses are not cells, and therefore not sensitive to such compounds. Viruses depend on the host cell's machinery, so it is hard to find a viral target that would leave the host cell unaffected.

Viruses depend on the host cell's machinery, so it is hard to find a viral target that would leave the host cell unaffected.

Why do antibiotics not work against viruses? Viruses do not contain antibiotic targets. Viruses are too small for antibiotics to bind to. Viruses are intercellular pathogens, which prevents antibiotics from getting to them. Viruses are antibiotic resistant

Viruses do not contain antibiotic targets.

Why is it more difficult to treat viral infections than it is to treat bacterial infections? Viruses are very similar to human cells. Viruses are smaller than human cells. Viruses use the host cell's processes to carry out their own reproduction. Viruses have cell walls.

Viruses use the host cell's processes to carry out their own reproduction.

antibiotic

a substance made by microorganism that in small amounts inhibits another microorganism

broad spectrum antibiotics

affect a broad range of gram-positive or gram-negative bacteria

A disk-diffusion test identifies __________. bactericidal agents only bacteriostatic agents only agents to which a test culture is sensitive, in terms of growth or survival minimal bactericidal concentration (MBC)

agents to which a test culture is sensitive, in terms of growth or survival

Simultaneous use of penicillin and tetracycline is often less effective than when either drug is used alone. This is called __________.

antagonism

A drug that inhibits peptidoglycan synthesis is __________.

antibacterial

sulfa drugs

block the cell's ability to synthesize essential metabolites.

A chemical that kills gram-positive bacteria and gram-negative bacteria would best be described as __________.

broad spectrum

How do antifungal drugs such as miconazole and amphotericin B function? by disrupting the plasma membrane by inhibiting protein synthesis by interfering with the processes of DNA replication and transcription by inhibiting cell wall synthesis

by disrupting the plasma membrane

Narrow spectrum antibiotics

drugs that affect a narrow range of microbial types

A drug that binds with sterols would injure __________.

eukaryotic plasma membranes

Natural Penicillins

extracted from cultures of penicillum fungi

Sulfonamides interfere with __________. folic acid synthesis in bacteria protein synthesis in helminths anaerobic metabolism in protozoa protein synthesis in fungi

folic acid synthesis in bacteria

Polyenes, azoles, and allylamines interfere with __________.

fungal cell membranes

Tetracyclines are effective against all of the following EXCEPT __________. intracellular rickettsias intracellular chlamydias gram-negative bacteria fungi gram-positive bacteria

fungi

An antimicrobial drug that inhibits peptidoglycan synthesis is most likely to be effective against __________.

gram-positive bacteria

If penicillin G is chosen as the best treatment for a given infection, what microorganisms are most likely the cause? viruses gram-positive bacteria fungi gram-negative bacteria

gram-positive bacteria

antibacterial antibiotics

inhibitors of cell wall synthesis

Penicillin

inhibits cell wall synthesis

Antimycobacterial antibiotics

isoniazid and ethambutol; inhibit synthesis of mycolic acids in cell walls of mycobacteria

Misuse of antibiotics leads to drug resistant bacterial populations by __________. killing off some bacteria, while inducing mutations in other bacteria killing off all susceptible bacteria, selecting for those bacteria that are naturally resistant weakening the susceptible bacteria, allowing them to get used to the antibiotic killing all the bacteria in a population

killing off all susceptible bacteria, selecting for those bacteria that are naturally resistant

minimal inhibitory concentration (MIC)

lowest concentration of drug that inhibits growth of pathogen

All of the following are antiprotozoan drugs EXCEPT __________. chloroquine metronidazole mefloquine mebendazole quinacrine

mebendazole

Chloroquine-resistant malaria may be treated with __________.

mefloquine

Which of the following is an antiprotozoan drug that interferes with anaerobic metabolism? erythromycin metronidazole chloroquine acyclovir

metronidazole

Semisynthetic penicillins are __________ antibiotics than is natural penicillin.

more effective

Ethambutol inhibits incorporation of mycolic acid into cell walls; therefore, it is effective against __________.

mycobacteria

Superinfection

occurs when a pathogen develops resistance to the drug being used or when normally resistant microbiota multiply

Many antifungal drugs target __________ in the fungal cell membrane.

sterols

A disadvantage of using broad-spectrum antibiotics for treating bacterial infections is the potential for __________.

superinfection

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 __________. antagonism synergism RNA interference mutual exclusion

synergism

Some drug combinations are __________; therefore, when taken together, they are more effective.

synergistic

antimicrobial drugs

synthetic substances that interfere with the growth of microbes; are either bactericidal or bacteriostatic

antifungal drugs

target the sterols in the plasma membrane

Rifampin blocks RNA polymerase and therefore inhibits __________.

transcription

Clindamycin binds to the 50S ribosomal subunit to inhibit translocation. This antibiotic stops __________. transcription in eukaryotes DNA synthesis in eukaryotes translation in prokaryotes transcription in prokaryotes

translation in prokaryotes

A nucleoside analog used to treat HIV infection is __________.

zidovudine