Micro Test #3- ch.20 Pearson

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.

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

Select all of the statements that accurately describe the origins and spread of antibiotic resistance.

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

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. Alteration of the drug's target site Inactivation of the drug by enzymes Blocking the drug's entry into the cell

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.

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

Bacterial transcription

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

Broad-spectrum antibiotics

What is meant by selective toxicity?

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

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

Chloroquine

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

Clotrimazole

Quinolones and fluoroquinolones act against what bacterial target?

DNA gyrase

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

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.

Which of the following mechanisms is antifungal?

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

Why is polymyxin only used on the skin?

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.

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?

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?

Neomycin

Which drug is NOT a nucleoside analog?

Nevirapine

In the figure, chloramphenicol binds to the 50S ribosome subunit. What effect would occur if this drug is administered to a eukaryote?

Nothing — eukaryotes have a 60S large ribosomal subunit, not a 50S. Submit

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

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

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

Which statement regarding tests for microbial susceptibility to chemotherapeutic agents is FALSE?

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

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. Antibiotic D Antibiotic A Antibiotic B Antibiotic C

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)?

There is not enough information to determine the MBC.

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?

These antibiotics interfere with protein synthesis within eukaryotic mitochondria.

Which of the following statements about drugs that competitively inhibit DNA polymerase or RNA polymerase is FALSE?

They cause cellular plasmolysis.

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

Why is it difficult to find good chemotherapeutic agents against viruses?

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 more difficult to treat viral infections than it is to treat bacterial infections?

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

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

broad spectrum

Antimicrobial peptides (AMPs) frequently work by

disrupting the plasma membrane.

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

Niclosamide prevents ATP generation in mitochondria. You would expect this drug to be effective against

helminths

The antibiotic tetracycline binds to the 30S subunit of the ribosome, as shown by the dark black bar on the right portion of the diagram in the figure. The effect is to

interfere with the attachment of the tRNA to mRNA-ribosome complex.

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 antibiotics is recommended for use against gram-negative bacteria?

polymyxin

More than half of our antibiotics are

produced by bacteria.

Which of the following does NOT affect eukaryotic cells?

semisynthetic penicillins

Many antifungal drugs target __________ in the fungal cell membrane.

sterols

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 __________.

synergism

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

synergistic

The antimicrobial drugs with the broadest spectrum of activity are

tetracyclines.

Use of antibiotics in animal feed leads to antibiotic-resistant bacteria because

the antibiotics kill susceptible bacteria, but the few that are naturally resistant live and reproduce, and their progeny repopulate the host animal.

Protozoan and helminthic diseases are difficult to treat because

their cells are structurally and functionally similar to human cells.

Rifampin blocks RNA polymerase and therefore inhibits __________.

transcription

The antibiotic actinomycin D binds between adjacent G-C pairs, thus interfering with

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