MCB 2000 CH 20

Broad spectrum

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

Superinfection(s)

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

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

A disk-diffusion test identifies __________. Disk-diffusion tests will indicate susceptibility and resistance to the antibiotics tested.

Eukaryotic plasma membranes

A drug that binds with sterols would injure __________.

Fungi

A drug that inhibits mitosis, such as griseofulvin, would be more effective against

Antibacterial

A drug that inhibits peptidoglycan synthesis is __________.

Zidovudine

A nucleoside analog used to treat HIV infection is __________.

False

Alexander Fleming performed the first clinical trials with penicillin, demonstrating its effectiveness as a chemotherapeutic agent.

Mebendazole

All of the following are antiprotozoan drugs EXCEPT __________. Mefloquine. Quinacrine. Mebendazole. Chloroquine. Metronidazole.

Gram-positive bacteria

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

True

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

PABA

Bacteria that are resistant to sulfonamide have enzymes that have a greater affinity for what?

Bacteria are prokaryotic.

Bacterial infections are easier to treat using chemotherapy than are other types of infections caused by other types of microorganisms. Why?

True

Because antifungal drugs such as amphotericin B target sterols in the plasma membrane, they are ineffective as antibacterial drugs.

Mefloquine or Lariam

Chloroquine-resistant malaria may be treated with __________.

Translation in prokaryotes

Clindamycin binds to the 50S ribosomal subunit to inhibit translocation. This antibiotic stops __________. The 50S ribosomal subunits are most commonly found in bacteria, so clindamycin inhibits bacterial protein synthesis. Eukaryotic cells also have ribosomes, but they are a different size.

When antibiotics are used indiscriminately.

Drug resistance occurs

Mycobacteria

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

By disrupting the plasma membrane

How do antifungal drugs such as miconazole and amphotericin B function? These antifungal drugs are effective against a wide range of fungal diseases.

Tetracycline interferes with the attachment of tRNA to the mRNA-ribosome complex

How does tetracycline inhibit protein synthesis? Tetracycline does interfere with the attachment of tRNA to the mRNA-ribosome complex. Streptomycin changes the shape of the 30S portion of the ribosome, which causes the mRNA to be read incorrectly. Chloremphenicol binds to the 50S portion of the ribosome and inhibits the formation of the peptide bond. Oxazolidinone prevents the 50S and 30S portions of the ribosome from coming together.

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

How might efflux pumps increase antibiotic resistance in bacteria?

Azole antibiotics.

Lamisil is an allylamine used to treat dermatomycoses. Lamisil's method of action is similar to that of

Sterols or ergosterol

Many antifungal drugs target __________ in the fungal cell membrane.

Bacteria

Mebendazole is used to treat cestode infections. It interferes with microtubule formation; therefore, it would NOT affect

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

Membrane transport proteins are required for which mode(s) of antibiotic resistance?

Produced by bacteria

More than half of our antibiotics are

Bacteria

Most of the available antimicrobial agents are effective against

It was the first antibiotic.

Penicillin was considered a "miracle drug" for all of the following reasons EXCEPT It was the first antibiotic. It has selective toxicity. It does not affect eukaryotic cells. It inhibits gram-positive cell wall synthesis. It kills bacteria.

Fungal cell membranes

Polyenes, azoles, and allylamines interfere with __________.

Their cells are structurally and functionally similar to human cells.

Protozoan and helminthic diseases are difficult to treat because

DNA gyrase

Quinolones and fluoroquinolones act against what bacterial target?

Transcription

Rifampin blocks RNA polymerase and therefore inhibits __________.

True

Semisynthetic penicillins are more effective antibiotics than is natural penicillin.

True

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

Folic acid synthesis in bacteria

Sulfanilamides interfere with __________. These antimicrobial agents target the synthesis of essential metabolites.

Fungi

Tetracyclines are effective against all of the following EXCEPT __________. Intracellular rickettsias. Intracellular chlamydias. Fungi. Gram-positive bacteria. Gram-negative bacteria

Kirby-Bauer

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

Trichomonas vaginalis

The drug Flagyl is commonly used to treat an STD caused by __________.

Inhibition of nucleic acid synthesis

The method of action of nucleoside analogs is __________.

Inhibition of protein synthesis

The mode of action for erythromycin is __________. Erythromycin inhibits protein synthesis. It is believed to work by blocking the "tunnel" formed by the complete ribosome as shown in Figure 20.4a.

Transduction.

The process of acquiring antibiotic resistance by means of bacteriophage activity is called

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

What is meant by selective toxicity?

The bacterium is neither killed nor inhibited by the antibiotic.

What is meant when a bacterium is said to become "resistant" to an antibiotic?

It inhibits penicillinase.

What is the benefit of combining penicillins with potassium clavulanate (clavulanic acid)? Potassium clavulanate is a beneficial addition to penicillin treatments.

Alteration of the target molecule

What is the mechanism of the resistance of MRSA to methicillin?

Inhibition of DNA synthesis

What is the method of action of nucleoside analogs?

The drug will kill or inhibit the growth of all of the sensitive bacterial cells

When a patient is treated with antibiotics, __________.

Ciprofloxacin

Which antibiotic inhibits replication?

Penicillin

Which antibiotic is overcome by beta-lactamases?

Posaconazole

Which antifungal drug was recently introduced to treat systemic fungal infections?

Isoniazid

Which antimicrobial works by inhibiting the synthesis of mycolic acid?

Flucytosine

Which compound would be the most useful to treat candidiasis?

Nevirapine

Which drug is NOT a nucleoside analog? Lamivudine. Nevirapine. Zidovudine. Ribavirin. Acyclovir

Clotrimazole

Which drug would be used to treat athlete's foot?

Sulfanilamide

Which of the following antibiotics inhibits folic acid synthesis?

Streptomycin

Which of the following antibiotics inhibits protein synthesis?

Erythromycin

Which of the following antibiotics is a common choice to treat streptococcal infections in children?

Erythromycin

Which of the following antibiotics is frequently used as an alternative for those who are allergic to penicillin?

Penicillin

Which of the following antimicrobial agents has the fewest side effects?

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

Which of the following best describes the mode of action of aminoglycosides? Common examples of aminoglycosides are streptomycin, neomycin, and gentamicin. These are all considered broad-spectrum antibiotics.

Rifampin

Which of the following drugs inhibits the synthesis of mRNA in bacteria?

Bacterial transcription

Which of the following is NOT a mechanism by which antibiotic resistance spreads horizontally among bacteria?

Sulfa drugs cause production of antimetabolites.

Which of the following is NOT a reason for the selective toxicity of sulfa drugs?

Neomycin

Which of the following is a broad-spectrum, topical antibacterial compound?

Ivermectin

Which of the following is an antihelminthic drug that causes paralysis of the worm?

Chloroquine

Which of the following is the drug of choice for the treatment of malaria?

Oseltamivir

Which of the following is used for treating influenza infections?

Inhibit ergosterol synthesis

Which of the following mechanisms is antifungal?

Silent mutation.

Which of the following mutations would not result in antibiotic resistance? Missense mutation. Nonsense mutation. Silent mutation. Frameshift insertion. Frameshift deletion.

Streptococcus pyogenes

Which of the following organisms would MOST likely be sensitive to natural penicillin?

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

Which of the following statements about antibiotics is true? Finding antibiotic-producing microorganisms is relatively common. However, most of them are already known or are of no or little clinical value.

They cause cellular plasmolysis.

Which of the following statements about drugs that competitively inhibit DNA polymerase or RNA polymerase is FALSE? They are used against viral infections. They can affect host cell DNA synthesis. They cause cellular plasmolysis. They interfere with protein synthesis. They can potentially cause mutations.

Trimethoprim is a structural analog of tetrahydrofolic acid.

Which of the following statements is false? Trimethoprim is a structural analog of dihydrofolic acid, not tetrahydrofolic acid.

They may be caused by antibiotic-resistant bacteria.

Which of the following statements is true about superinfections?

Broad-spectrum antibiotics

Which of the following types of antibiotics is most likely to be associated with the development of a superinfection?

Ampicillin

Which of the following types of penicillin is effective against Gram negative bacteria? The side chain of Apmicillin allows it to penetrate the cell wall of Gram negative bacteria. Penicillins G and V are the naturally occurring penicillins and are only effective against Gram positive bacteria. Oxacillin is resistant to action of penicillinase, but is only effective against Gram positive bacteria

The two antibiotics are synergistic.

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? This enlarged zone of inhibition may indicate that the combination of the two drugs is more effective than either drug alone.

Humans and other animal hosts lack peptidoglycan cell walls.

Why are chemotherapeutic agents that work on the peptidoglycan cell wall of bacteria a good choice of drug?

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 is it difficult to find good chemotherapeutic agents against viruses?

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

Why is it more difficult to treat viral infections than it is to treat bacterial infections? Think about the life cycle of a virus and its specific needs for survival.

It produces a modified version of the molecule that is targeted by the drug.

Why is methicillin-resistant Staphylococcus aureus (MRSA) methicillin resistant? MRSA strains have developed resistance to a wide range of penicillins and cephalosporins. MRSA strains contain a modified version of penicillin-binding proteins on their membrane, which still weakly bind the antibiotic but continue to enable them to synthesize their cell wall for survival.

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.

Why is polymyxin only used on the skin?

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

Why would an efflux pump for penicillin located on a bacterial cell membrane not be effective at providing resistance to the drug?

The correct answer cannot be determined from the information provided.

You are reviewing the following results of a disk- diffusion antibiotic susceptibility test on an isolate of Staphylococcus aureus: Antibiotic A: ZI (zone of inhibition) = 0 millimeters; Antibiotic B: ZI = 23 millimeters; Antibiotic C: ZI = 16 millimeters; Antibiotic D: ZI = 19 millimeters Which antibiotic is bactericidal?

25 mg/ml

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 __________.

The MBC cannot be determined from the information provided.

You have a 200-milligram-per-milliliter antibiotic solution. You prepare serial dilutions (1:2, 1:4, etc.) of the antibiotic. You then inoculate each tube with Salmonella. Bacteria grow in tubes 4, 5, and 6. What is the MBC (minimum bactericidal concentration)?

100 mg/ml

You have a 200-milligram-per-milliliter antibiotic solution. You prepare serial dilutions (1:2, 1:4, etc.) of the antibiotic. 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 tubes 2 through 3. What is the MBC (minimum bactericidal concentration)?