Chapter 20 Mastering Microbiology

What is meant by selective toxicity?

Chemotherapeutic agents should work on certain types of pathogens.
Chemotherapeutic agents should have only one mode of action.
Chemotherapeutic agents should work on many different targets on a pathogen.
Chemotherapeutic agents should act against the pathogen and not the host.

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

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

They are less expensive that other chemotherapeutic agents.
Bacteria are especially sensitive to these compounds.
Humans and other animal hosts lack peptidoglycan cell walls.
The drugs also work against DNA gyrase.

Humans and other animal hosts lack peptidoglycan cell walls.

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.
It is sensitive to degradation by acid, making oral delivery unsuitable.
It can disrupt the metabolic pathways found in humans.
It has no effect on bacteria that live in the GI tract.

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.

Quinolones and fluoroquinolones act against what bacterial target?

Cell membranes
Cell walls
Bacterial ribosomes
DNA gyrase
Metabolic pathways unique to bacteria

DNA gyrase

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

There is no effective way to deliver the drug to the virus.
Viruses depend on the host cell’s machinery, so it is hard to find a viral target that would leave the host cell unaffected.
Viruses are not cells, and therefore not sensitive to such compounds.
Viruses infect both bacteria and human cells.

Viruses depend on the host cell’s machinery, so it is hard to find a viral target that would leave the host cell unaffected.

If penicillin G is chosen as the best treatment for a given infection, what microorganisms are most likely the cause?

viruses
fungi
gram-positive bacteria
gram-negative bacteria

gram-positive bacteria

Why is methicillin-resistant Staphylococcus aureus (MRSA) methicillin resistant?

It has an enzyme that destroys methicillin.
It actively pumps the antibiotic out of the cell.
It produces a modified version of the molecule that is targeted by the drug.
The bacteria are able to prevent entry of the drug into the cell.

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

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

Viruses have cell walls.
Viruses use the host cell’s processes to carry out their own reproduction.
Viruses are smaller than human cells.
Viruses are very similar to human cells.

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

A new bacterial molecule is discovered. This molecule binds to an antibiotic and facilitates the binding of a phosphate group, thus inactivating the antibiotic. Which category best describes the mechanism of antibiotic resistance conferred by this molecule?

bacterial enzymes
altered porins
conjugation
rapid efflux of the antibiotic

bacterial enzymes

Which antibiotic is overcome by beta-lactamases?

Tetracycline
Sulfonamide
Penicillin
Tetracycline, Penicillin, and Sulfonamide are all affected by beta-lactamase.

Penicillin

How might efflux pumps increase antibiotic resistance in bacteria?

Resistant bacteria may have a greater number of efflux pumps on their cell surfaces.
Some bacteria can decrease the specificity of their efflux pumps, increasing the number of different antibiotics the pumps can eliminate.
Some bacteria can change the chemical structure of the antibiotic.
Efflux pumps can never be modified to increase antibiotic resistance.
Resistant bacteria can have more efflux pumps, and can have less specific efflux pumps.

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

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

PABA
Sulfonamide
Tetrahyrdrofolic acid
Tetracycline

PABA

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

The efflux pumps would not stop penicillin from blocking metabolic pathways.
There are fewer efflux pumps on the cell membrane.
The cell membrane is the target of penicillin.
Penicillin disrupts the cell wall, which is located outside of the cell membrane.

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

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

Modification of a metabolic enzyme
Beta-lactamases
Modification of a porins
Efflux pumps
Efflux pumps, beta-lactamases, and modification of porins all utilize membrane transport proteins.

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

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

The antibiotic kills or inhibits the bacterium.
The antibiotic is metabolized by the bacterium, providing more energy for growth of the cell.
The bacterium is neither killed nor inhibited by the antibiotic.
The antibiotic mutates in a way that benefits the bacterium.

The bacterium is neither killed nor inhibited by the antibiotic.

When a patient is treated with antibiotics, __________.

mutations occur in all of the bacterial cells
sensitive bacterial cells multiply uncontrollably
the drug will kill or inhibit the growth of all of the sensitive bacterial cells
the drug will kill or inhibit the growth of all of the resistant bacterial cells
mutations will occur in the sensitive bacterial cells, but not in the resistant bacterial cells

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

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

transduction.
R-plasmid acquisition.
point mutation.
transformation.

transduction.

Which of the following mutations would not result in antibiotic resistance?

Missense mutation
Nonsense mutation
Silent mutation
Frameshift insertion
Frameshift deletion

Silent mutation

R-plasmids are most likely acquired via

transduction.
transformation.
bacterial conjugation.
translation.

bacterial conjugation.

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 __________.

antagonism
synergism
mutual exclusion
RNA interference

synergism

Which of the following would be selective against the tubercle bacillus?

streptomycin – inhibits protein synthesis
bacitracin – inhibits peptidoglycan synthesis
vancomycin – inhibits peptidoglycan synthesis
ethambutol – inhibits mycolic acid synthesis
streptogramin – inhibits protein synthesis

ethambutol – inhibits mycolic acid synthesis

Drug resistance occurs

against antibiotics and not against synthetic chemotherapeutic agents.
when antibiotics are taken after the symptoms disappear.
when antibiotics are used indiscriminately.
because bacteria are normal microbiota.
All of the answers are correct.

when antibiotics are used indiscriminately.

Which of the following statements about drug resistance is FALSE?

It may be due to increased uptake of a drug.
It is found only in gram-negative bacteria.
It may be due to enzymes that degrade some antibiotics.
It may be transferred from one bacterium to another during conjugation.
It may be carried on a plasmid.

It is found only in gram-negative bacteria.

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

penicillinase-producing Neisseria gonorrhoeae
Penicillium
helminths
Mycoplasma
Streptococcus pyogenes

Streptococcus pyogenes

The antimicrobial drugs with the broadest spectrum of activity are
macrolides.
aminoglycosides.
chloramphenicol.
tetracyclines.
penicillin G.

tetracyclines.

To date, most of our natural antibiotics have been found to be produced by members of what genus?

Bacillus
Penicillium
Streptomyces
Paenibacillus
Cephalosporium

Streptomyces

More than half of our antibiotics are

synthesized in laboratories.
produced by fungi.
produced by Fleming.
produced by bacteria.
produced by eukaryotic organisms.

produced by bacteria.

Which of the following antibiotics is recommended for use against gram-negative bacteria?
cephalosporin
polymyxin
penicillin
bacitracin
polyenes

polymyxin

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

streptomycin
chloramphenicol
penicillin
tetracycline
erythromycin

penicillin

In what way are semisynthetic penicillins and natural penicillins alike?

Both are based on β-lactam.
Both are bactericidal.
Both are resistant to stomach acids.
Both are resistant to penicillinase.
Both are broad spectrum.

Both are based on β-lactam.

Penicillin was considered a "miracle drug" for all of the following reasons EXCEPT

it was the first antibiotic.
it kills bacteria.
it has selective toxicity.
it does not affect eukaryotic cells.
it inhibits gram-positive cell wall synthesis.

it was the first antibiotic.

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.
A broth dilution test is often used to determine MIC and MBC of an antimicrobial drug.
During the Kirby-Bauer test, a Petri plate with agar medium is uniformly inoculated with a standardized amount of a test organism.
During a disk-diffusion test, a clear zone around the test disk indicates that growth was inhibited.

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