Chapter 20 - Antimicrobial Drugs

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)?

100 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 __________.

25 mg/ml

__________ discovered penicillin and the first clinical trials in 1940 demonstrated its effectiveness as a chemotherapeutic agent.

Alexander Fleming

Which of the following are common targets for bacterial resistance to antibiotics?

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

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

Bacteria are prokaryotic.

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

Chloroquine

Which of the following mechanisms is antifungal?

Inhibit ergosterol synthesis

Which antimicrobial works by inhibiting the synthesis of mycolic acid?

Isoniazid

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

Kirby-Bauer

Which of the following statements about antibiotics is true?

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

Which drug is NOT a nucleoside analog?

Nevirapine

Which of the following antibiotics inhibits protein synthesis?

Streptomycin

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

Sulfa drugs cause production of antimetabolites.

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?

The correct answer 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)?

There is not enough information to determine the MBC.

Which of the following statements is true about superinfections?

They may be caused by antibiotic-resistant bacteria.

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

Trichomonas vaginalis

A disk-diffusion test identifies __________.

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

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

antibiotics

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

bacterial transcription

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

broad spectrum

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

broad spectrum antibiotics

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

clotrimazole

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?

erythromycin

A drug that binds with sterols would injure __________.

eukaryotic plasma membranes

Polyenes, azoles, and allylamines interfere with __________.

fungal cell membranes

Tetracyclines are effective against all of the following EXCEPT __________.

fungi

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

gram-positive bacteria

What is the method of action of nucleoside analogs?

inhibition of DNA synthesis

What is the benefit of combining penicillins with potassium clavulanate (clavulanic acid)?

it inhibits penicillinase

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

ivermectin

All of the following are antiprotozoan drugs EXCEPT __________.

mebendazole

Chloroquine-resistant malaria may be treated with __________.

mefloquine

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

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

neomycin

Which of the following is used for treating influenza infections?

oseltamivir

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

posaconazole

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

rifampin

Many antifungal drugs target __________ in the fungal cell membrane.

sterols

Which of the following antibiotics inhibits folic acid synthesis?

sulfanilamide

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

superinfection

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

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?

the 2 antibiotics are synergistic

Rifampin blocks RNA polymerase and therefore inhibits __________.

transcription

Clindamycin binds to the 50S ribosomal subunit to inhibit translocation. This antibiotic stops __________.

translation in prokaryotes

A nucleoside analog used to treat HIV infection is __________.

zidovudine