Chapter 20

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)? 12.5 mg/ml 25 mg/ml 50 mg/ml 100 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 __________. 12.5 mg/ml 25 mg/ml 50 mg/ml 200 mg/ml none of the listed choices

25 mg/ml

Consider the different mechanisms through which antibiotics inhibit microbial growth, and consider what changes in the microbe might enable it to resist the inhibitory effects of antibiotics. Select all of the statements that describe a mechanism that would enable a microorganism to resist the action of an antibiotic. A transport mechanism that rapidly transports antibiotic through the plasma membrane into the cytoplasm is developed. Altered porins in the cell wall block passage of antibiotic through the cell wall. An enzyme that destroys the antibiotic is produced. An altered target enhances the binding of antibiotic. A microbe develops a transport mechanism in the plasma membrane that rapidly pumps antibiotic out of the bacterial cell. Target site is modified, so that an antibiotic is unable to bind to its target.

Altered porins in the cell wall block passage of antibiotic through the cell wall. An enzyme that destroys the antibiotic is produced. A microbe develops a transport mechanism in the plasma membrane that rapidly pumps antibiotic out of the bacterial cell. Target site is modified, so that an antibiotic is unable to bind to its target.

Which of the following choices correctly matches the class of antibiotic and its mode of action? Select all that apply. Aminoglycosides and tetracyclines are inhibitors of protein synthesis. Penicillins and cephalosporins inhibit nucleic acid synthesis. Sulfonamides inhibit the synthesis of essential metabolites. Lipopeptides inhibit cell wall synthesis.

Aminoglycosides and tetracyclines are inhibitors of protein synthesis Sulfonamides inhibit the synthesis of essential metabolites.

Identify the statements below that accurately describe the mechanisms through which organisms acquire antibiotic resistance. Select all of the statements that accurately describe the origins and spread of antibiotic resistance. Antibiotics cause an increase in the rate of horizontal gene transfer. Antibiotics cause mutations; heavy antibiotic use directly leads to mutations in microbes, giving rise to antibiotic resistance. Antibiotic resistance is readily transmitted to the next generation during binary fission. Antibiotic-resistance genes can be passed horizontally via bacterial conjugation. Antibiotics select for those microbes that have developed resistance, increasing their frequency in the bacterial population. Antibiotic-resistance genes can be passed from one bacterium to another by bacterial transformation. Antibiotic-resistance genes can be passed horizontally via transduction. Mutations are the ultimate source of antibiotic-resistance genes.

Antibiotic resistance is readily transmitted to the next generation during binary fission. Antibiotic-resistance genes can be passed horizontally via bacterial conjugation. Antibiotics select for those microbes that have developed resistance, increasing their frequency in the bacterial population. Antibiotic-resistance genes can be passed from one bacterium to another by bacterial transformation. Antibiotic-resistance genes can be passed horizontally via transduction. Mutations are the ultimate source of antibiotic-resistance genes.

Why does the physician start Caleb on the antibiotic azithromycin before laboratory results come back? Antibiotic therapy is started before culture results are obtained because all of the pathogens that cause lower respiratory infections grow very slowly in the laboratory. Caleb would die if treatment were delayed until cultures grew. Antibiotic therapy is started with a broad-spectrum antibiotic because broad-spectrum antibiotics are effective against many gram-positive and many gram-negative bacteria. Antibiotic therapy is started with a narrow-spectrum antibiotic because narrow-spectrum antibiotics are effective against many gram-positive and many gram-negative bacteria. Antibiotic therapy is started with a broad-spectrum antibiotic because broad-spectrum antibiotics are effective against only gram-negative bacteria.

Antibiotic therapy is started with a broad-spectrum antibiotic because broad-spectrum antibiotics are effective against many gram-positive and many gram-negative bacteria.

Bacterial infections are easier to treat using chemotherapy than are other types of infections caused by other types of microorganisms. Why? Bacteria are more sensitive to chemicals. Bacteria are smaller than the other types of pathogens. Bacteria are prokaryotic and thus, have targets different than eukaryotic cells. Bacteria grow more slowly.

Bacteria are prokaryotic and thus, have targets different than eukaryotic cells.

Why does Dr. Bell start Caleb on HIV therapy in addition to the antibiotics used to treat the tuberculosis? Dr. Bell prescribes Caleb extra medications to ensure a high enough dose to completely eliminate both pathogens. Dr. Bell prescribes Caleb HIV therapy because he does not think that Caleb will complete his regimen of antibiotics. Dr. Bell prescribes Caleb HIV therapy because the virus is not affected by the antibiotics used to treat tuberculosis. Dr. Bell prescribes Caleb HIV therapy because in conjunction with the antibiotics, it will eliminate the tuberculosis.

Dr. Bell prescribes Caleb HIV therapy because the virus is not affected by the antibiotics used to treat tuberculosis.

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

False

Undergrowth of fungi after antibiotic use is commonly referred to as a superinfection. True False

False

Which of the following is mismatched? Ehrlich - "magic bullet" theory Florey and Chain - identification of Penicillium as the producer of penicillin Kirby and Bauer - disc-diffusion method Fleming - initial identification of penicillin's effect on gram-positive microbial growth None of these is mismatched.

Florey and Chain - identification of Penicillium as the producer of penicillin

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

It inhibits penicillinase.

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

Kirby-Bauer

Which of the following contribute to drug resistance in M. tuberculosis? Select all that apply. Many individuals fail to complete their entire regimen of antibiotics. Some physicians prescribe the wrong medication, the wrong dosage, or the wrong length of time for treating tuberculosis. In many areas, tuberculosis antibiotics are unavailable or of poor quality. M. tuberculosis is an acid-fast bacterium; this characteristic allows it to become resistant to antibiotics faster than other bacteria.

Many individuals fail to complete their entire regimen of antibiotics. Some physicians prescribe the wrong medication, the wrong dosage, or the wrong length of time for treating tuberculosis. In many areas, tuberculosis antibiotics are unavailable or of poor quality.

Which of the following statements about antibiotics is true? Antibiotics are not typically produced by microorganisms growing in their natural environment. The finding of antibiotic-producing microorganisms is a rare event. Most of our antibiotics are produced by Streptomyces, a genus of filamentous soil bacteria. 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.

Which of the following statements about antibiotics is true? 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. Antibiotics are not typically produced by microorganisms growing in their natural environments. The finding of antibiotic-producing microorganisms is a rare event.

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

To date, most of our natural antibiotics have been found to be produced by members of what genus? Paenibacillus Streptomyces Bacillus Penicillium Cephalosporium

Streptomyces

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

Sulfa drugs cause production of antimetabolites

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 The MBC cannot be determined from the information provided.

The MBC 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 millimetersAntibiotic B: ZI = 23 millimetersAntibiotic C: ZI = 16 millimetersAntibiotic D: ZI = 19 millimetersWhich antibiotic is bactericidal? Antibiotic A Antibiotic B Antibiotic C Antibiotic D The correct answer cannot be determined from the information provided.

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 antagonistic. The two antibiotics are bacteriostatic. The two antibiotics are bactericidal. The two antibiotics are synergistic.

The two antibiotics are synergistic.

There are a large number of antibiotics that inhibit protein synthesis at 70S ribosomes found in bacterial cells but do not interfere with protein synthesis at the 80S ribosomes found in eukaryotic cells. Some of these antibiotics bind to the smaller ribosomal subunit and interfere with the reading of the mRNA code, whereas others bind to the larger ribosomal subunit and inhibit the formation of peptide bonds. Unfortunately, some of the antibiotics that inhibit protein synthesis in bacteria exhibit some toxicity to the eukaryotic host cells as well. What is the most likely reason for this toxicity to the host cell? Select the correct answer. These antibiotics interfere with DNA replication in eukaryotic cell nuclei. These antibiotics plug up the membrane transport mechanisms in eukaryotic cells. These antibiotics bond to eukaryotic tRNA. These antibiotics interfere with protein synthesis within eukaryotic mitochondria. These antibiotics bind to eukaryotic cytoplasmic ribosomes.

These antibiotics interfere with protein synthesis within eukaryotic mitochondria.

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 __________. Neisseria gonorrhoeae Trichomonas vaginalis Treponema pallidum HIV herpesvirus

Trichomonas vaginalis

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

True

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

True

Semisynthetic penicillins are more effective antibiotics than is natural penicillin. True False

True

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

True

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

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

What is the mechanism of the resistance of MRSA to methicillin? alteration of the target molecule blocking the entry of the methicillin efflux of the methicillin enzymatic destruction of the methicillin

alteration of the target molecule

A drug that inhibits peptidoglycan synthesis is __________. antiprotozoan antiviral antifungal antibacterial

antibacterial

Which of the following is NOT a mechanism by which antibiotic resistance spreads horizontally among bacteria? transduction plasmid transfer bacterial conjugation bacterial transcription

bacterial transcription

A chemical that kills gram-positive bacteria and gram-negative bacteria would best be described as __________. selectively toxic broad spectrum narrow spectrum specific

broad spectrum

Which of the following types of antibiotics is most likely to be associated with the development of a superinfection? broad-spectrum antibiotics bacteriostatic antibiotics β-lactam antibiotics bactericidal antibiotics narrow-spectrum antibiotics

broad-spectrum antibiotics

Which of the following types of antibiotics is most likely to be associated with the development of a superinfection? narrow-spectrum antibiotics beta-lactam antibiotics bacteriostatic antibiotics bactericidal antibiotics broad-spectrum antibiotics

broad-spectrum antibiotics

Which of the following is the drug of choice for the treatment of malaria? nifurtimox iodoquinol quinacrine Flagyl chloroquine

chloroquine

Which antibiotic inhibits replication? ciprofloxacin rifampin Both of the listed antibiotics inhibit replication. Neither of the listed antibiotics inhibits replication.

ciprofloxacin

Which drug would be used to treat athlete's foot? amantadine chloroquine clotrimazole polymyxin B neomycin

clotrimazole

Which drug would be used to treat athlete's foot? neomycin amantadine chloroquine polymyxin B clotrimazole

clotrimazole

Which of the following antibiotics is a common choice to treat streptococcal infections in children? tetracycline neomycin rifampin trimethoprim erythromycin

erythromycin

Which of the following antibiotics is frequently used as an alternative for those who are allergic to penicillin? streptomycin vancomycin ethambutol erythromycin amoxicillin

erythromycin

A drug that binds with sterols would injure __________. DNA fungal cell walls eukaryotic plasma membranes bacterial cell walls

eukaryotic plasma membranes

A drug that binds with sterols would injure __________. eukaryotic plasma membranes DNA fungal cell walls bacterial cell walls

eukaryotic plasma membranes

Polyenes, azoles, and allylamines interfere with __________. viruses fungal cell membranes cell walls in gram-negative bacteria cell membranes in gram-positive bacteria

fungal cell membranes

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

fungi

An antimicrobial drug that inhibits peptidoglycan synthesis is most likely to be effective against __________. fungi protozoan parasites gram-positive bacteria viruses gram-negative bacteria

gram-positive bacteria

An antimicrobial drug that inhibits peptidoglycan synthesis is most likely to be effective against __________. gram-negative bacteria gram-positive bacteria viruses fungi protozoan parasites

gram-positive bacteria

Which of the following mechanisms is antifungal? inhibit 70S ribosomes interfere with anaerobic metabolism inhibit peptidoglycan synthesis inhibit ergosterol synthesis cause muscle spasms

inhibit ergosterol synthesis

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

inhibition of DNA synthesis

The method of action of nucleoside analogs is __________. inhibition of nucleic acid synthesis disruption of plasma membrane inhibition of protein synthesis inhibition of cell wall synthesis

inhibition of nucleic acid synthesis

The mode of action for erythromycin is __________. inhibition of protein synthesis inhibition of nucleic acid synthesis inhibition of essential metabolite synthesis inhibition of cell wall synthesis

inhibition of protein synthesis

Which antimicrobial works by inhibiting the synthesis of mycolic acid? methicillin chloramphenicol penicillin isoniazid vancomycin

isoniazid

Which of the following is an antihelminthic drug that causes paralysis of the worm? praziquantel ivermectin mebendazole niclosamide

ivermectin

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

mebendazole

Ethambutol inhibits incorporation of mycolic acid into cell walls; therefore, it is effective against __________. fungi gram-positive bacteria mycoplasmas mycobacteria

mycobacteria

Which of the following is a broad-spectrum, topical antibacterial compound? caspofungin bacitracin polymyxin B neomycin

neomycin

Which drug is NOT a nucleoside analog? lamivudine zidovudine ribavirin nevirapine acyclovir

nevirapine

Which of the following is used for treating influenza infections? interferon indinavir pentamidine isethionate acyclovir oseltamivir

oseltamivir

Cells that synthesize ________________ develop resistance to penicillin through their ability to hydrolyze the beta lactam ring of the penicillin.

penicillinases, beta-lactamases

Which antifungal drug was recently introduced to treat systemic fungal infections? miconazole clotrimazole amphotericin B posaconazole tolnaftate

posaconazole

Which of the following drugs inhibits the synthesis of mRNA in bacteria? rifampin ethambutol trimethoprim ampicillin polymyxin B

rifampin

Many antifungal drugs target __________ in the fungal cell membrane.

sterols, ergosterol

Which of the following antibiotics inhibits protein synthesis? cephalosporin streptomycin rifampin isoniazid vancomycin

streptomycin

If Caleb's strain of M. tuberculosis is sensitive to antibiotic treatment, which of the following could be used to treat his infection? Select all that apply. streptomycin penicillins and cephalosporins isoniazid and ethambutol rifampin

streptomycin isoniazid and ethambutol rifampin

Which of the following antibiotics inhibits folic acid synthesis? tetracycline chloramphenicol neomycin ampicillin sulfanilamide

sulfanilamide

Which of the following antibiotics inhibits folic acid synthesis? tetracycline sulfanilamide neomycin chloramphenicol ampicillin

sulfanilamide

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

superinfection

Rifampin blocks RNA polymerase and therefore inhibits __________. transcription DNA synthesis translation cell wall synthesis

transcription

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

translation in prokaryotes

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

translation in prokaryotes

A nucleoside analog used to treat HIV infection is __________. amantadine ribavirin acyclovir zidovudine praziquantel

zidovudine