Mastering Microbiology – Chapter 20

Which antibiotic is overcome by beta-lactamases?

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

A: 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

A: 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

A: PABA

Why would an efflux pump for penicillin located on a bacterial cel 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

A: 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?

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

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

What is meant by selective toxicity?

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

A: 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?

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

A: Humans and other animal hosts lack peptidoglycan cell walls

Why is polymyxin only used on the skin?

>It has no effect on bacteria that live in the GI tract
>It is sensitive to degradation by acid, making oral delivery unsuitable
>It can also damage living human cell membranes, but the drug is safely used on the skin, where the other layers of cells are dead
>It can disrupt the metabolic pathways found in humans

A: It can also damage living human cell membranes, but the drug is safely used on the skin, where the other layers of cells are dead

Quinolone and fluoroquinolone act against what bacterial target?

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

A: DNA gyrase

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

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

A: 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
>gram-positive bacteria
>gram-negative bacteria
>fungi

A: gram-positive bacteria

Sulfanilamides interfere with

>protein synthesis in helminths
>anaerobic metabolism in protozoa
>protein synthesis in fungi
>folic acid synthesis in bacteria

A: folic acid synthesis in bacteria

Certain cancer cells have ABC transport molecules at the cell surface. These transporters use energy from ATP to move chemotherapeutic agents out of the cell. Which of the following do you think these transporters are most closely related to?

>beta-lactamase
>membrane pumps
>conjugation pilus
>altered porins

A: membrane pumps

A researcher creates an antibiotic that binds to a protein present only on B. anthracis (the causative agent of anthrax), lysing the cell from the outside. After a couple of years using this antibiotic, some resistant organisms are found. Which of the following best outlines the mechanism for the development of this resistance?

>cell division of B. anthracis –>altered porins –> resistant bacterium
>mutation in B. anthracis –>altered porins –>resistant bacterium
>cell division of B. anthracis –>altered target –>resistant bacterium
>mutation in B. anthracis –>altered target –>resistant bacterium

A: mutation in B. anthracis –>altered target –>resistant bacterium

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

A: bacterial enzymes

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
>RNA interference
>mutual exclusion

A: synergism

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

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

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

>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
>It has an enzyme that destroys methicillin
>It actively pumps the antibiotic out of the cell

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

How do anti fungal drugs such as miconazole and amphotericin B function?

>by disrupting the plasma membrane
>by interfering with the processes of DNA replication and transcription
>by inhibiting cell wall synthesis
>by inhibiting protein synthesis

A: by disrupting the plasma membrane

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 fro growth of the cell
>The bacterium is neither killed nor inhibited by the antibiotic
>The antibiotic mutates in a way that benefits the bacterium

A: 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 the resistant bacterial cells
>mutations will occur in the sensitive bacterial cells, but not in the resistant bacterial cells

A: 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

A: transduction

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

>Missense mutation
>Nonsense mutation
>Silent mutation
>Frameshift insertion
>Frameshift deletion

A: Silent mutation

R-plasmids are most likely acquired via

>bacterial conjugation
>translation
>transformation
>transduction

A: bacterial conjugation