Chapter 20 Mastering Micro

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 50 mg/ml 25 mg/ml 12.5 mg/ml

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

All are common targets for bacterial resistance to antibiotics.

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

Bacterial transcription

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

Clotrimazole

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

Inhibit ergosterol synthesis

What is the method of action of nucleoside analogs?

Inhibition of DNA synthesis

Which antimicrobial works by inhibiting the synthesis of mycolic acid?

Isoniazid

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

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

Kirby-Bauer

Which of the following statements about antibiotics is true? Antibiotics are not typically produced by microorganisms growing in their natural environments. The finding of antibiotic-producing microorganisms is a rare event. Penicillin was first discovered by two researchers named Florey and Chain. 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? Polymyxin B Bacitracin Neomycin Caspofungin

Neomycin

Which of the following is used for treating influenza infections? Oseltamivir Interferon Acyclovir Pentamidine isethionate Indinavir

Oseltamivir

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

Sulfa drugs cause production of antimetabolites.

Which of the following antibiotics inhibits folic acid synthesis? Neomycin Sulfanilamide Chloramphenicol Tetracycline Ampicillin

Sulfanilamide

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.

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 synergistic.

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)? 12.5 mg/ml 25 mg/ml 50 mg/ml There is not enough information to determine the MBC.

There is not enough information to determine the MBC.

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

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

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

bacteria are prokaryotic

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 of the following is the drug of choice for the treatment of malaria? Iodoquinol Quinacrine Flagyl Nifurtimox Chloroquine

chloroquine

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 Streptomycin Ethambutol Vancomycin Amoxicillin

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 __________. gram-negative bacteria intracellular chlamydias intracellular rickettsias gram-positive bacteria fungi

fungi

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

gram pos. bacteria

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

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

nevirapine

Which antifungal drug was recently introduced to treat systemic fungal infections? Posaconazole Clotrimazole Tolnaftate Amphotericin B Miconazole

posaconazole

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

rifampin

Many antifungal drugs target __________ in the fungal cell membrane.

sterols

Which of the following antibiotics inhibits protein synthesis?

streptomycin

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

Rifampin blocks RNA polymerase and therefore inhibits __________.

transcription

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

translation in prokaryotes

A nucleoside analog used to treat HIV infection is __________.

zidovudine