Microbiology: MCB 3020 Smartwork 5 Chapter 27 Home Work Flashcards

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Antibiotics were used clinically beginning in the
Choose one:

A. 1940s.

B. 1990s.

C. 1840s.

D. 1740s.

A. 1940s.

Antibiotic use took off in the 1940s and saved countless lives during World War II.


Penicillin inhibits peptidoglycan synthesis in bacterial cell walls. Humans do not have cell walls. This is an example of
Choose one:

A. spectrum of activity.

B. selective toxicity.

C. allergic sensitivity.

D. minimum inhibitory concentration.

B. selective toxicity.

Selective toxicity is the ability of antibiotics to harm pathogens but not humans. Since penicillin targets a cell structure not present in humans it exhibits selective toxicity. Spectrum of activity indicates which microbes the antibiotic is effective against. The minimum inhibitory concentration is the lowest concentration of drug that prevents growth of an organism.


Suppose an exponentially growing culture of bacteria is treated with a potential antimicrobial compound. Over the next few hours, cell doubling stops (untreated, control cultures continue doubling), but the cells remain metabolically active. This antimicrobial compound is
Choose one:

A. bacteriostatic.

B. broad spectrum.

C. narrow spectrum.

D. bactericidal.

A. bacteriostatic.

Bactericidal antibiotics kill microbes; bacteriostatic antibiotics only inhibit growth. The cells remained metabolically active, meaning they were not killed. However, growth was halted so the compound is bacteriostatic, but not bactericidal. Spectrum of activity would not be measured this way.

card image

What is shown in the figure below?

Choose one:

A. Patient sensitivity to various drugs

B. Minimum inhibitory concentration strip test

C. Kirby-Bauer assay

D. Test of bacteriostatic versus bacteriocidal activity for various antibiotics

C. Kirby-Bauer assay

The Kirby-Bauer assay can test the susceptibility of a particular microbe for up to 12 antibiotics in an agar diffusion test. An MIC strip test only examines a single antibiotic. Neither test discriminates patient sensitivity or whether the drug is bacteriostatic or bacteriocidal.


To test the minimal inhibitory concentration (MIC) of a new antibiotic, drug concentrations of 1,000 μg/ml, 500 μg/ml, 250 μg/ml, and 125 μg/ml were incubated with the target bacteria. Bacterial growth was observed in the two lower concentrations of the drug (250 and 125 μg/ml) but not at the two higher concentrations. The MIC is
Choose one:

A. between 499 and 251 μg/ml.

B. between 1,000 and 500 μg/ml.

C. less than 125 μg/ml.

D. between 250 and 125 μg/ml.

A. between 499 and 251 μg/ml.

The MIC is the lowest concentration of the drug that prevents growth of an organism. Growth occurred at 250 μg/ml, but not at 500 μg/ml, so the MIC is between these two concentrations.


Which of the following structures or activities is a target for some antibiotics because it is absent from human cells?
Choose one:

A. Ribosomes

B. Cell wall

C. DNA replication

D. RNA synthesis

B. Cell wall

Animal cells lack cell walls. Both microbial and human cells replicate their DNA and perform transcription. Both microbial and human cells have ribosomes, although the ribosomes do differ in sensitivity to several antibiotics.


The selective toxicity of the sulfa drugs is due to the fact that bacteria
Choose one:

A. polymerize nucleotides into nucleic acids and mammals do not.

B. have cell walls and mammals do not.

C. can take up sulfa drugs and convert them to a toxic compound; mammalian cells cannot take up or convert the sulfa drugs.

D. synthesize folic acid and mammals use preformed folic acid.

D. synthesize folic acid and mammals use preformed folic acid.

Humans rely on preformed dietary folic acid, whereas bacteria synthesize their own folic acid. Sulfa drugs inhibit the bacterial folic acid synthetic pathway, a pathway not found in humans.


Protein synthesis inhibitor antibiotics
Choose one:

A. are bactericidal.

B. interfere with translation.

C. all affect the ribosomal 30S subunit.

D. include antibiotics such as methicillin and actinomycin D.

B. interfere with translation.

Translation is protein synthesis on a ribosome. Most protein synthesis inhibitor antibiotics tend to be bacteriostatic. They have different mechanisms of action; some affect the 50S subunit. Methicillin and actinomycin D are not protein synthesis inhibitors.


Beta-lactamase can provide resistance to
Choose one:

A. tetracycline.

B. vancomycin.

C. bacitracin.

D. penicillin

D. penicillin.

Penicillin is a beta-lactam antibiotic and can be cleaved by beta-lactamase–expressing bacteria. Bacitracin, vancomycin, and tetracycline have different chemical structures that are not affected by beta-lactamase.


Antibiotic-producing organisms can resist the effects of the antibiotic by all EXCEPT which of the following?
Choose one:

A. They modify the drug target in their cells to prevent drug interaction.

B. They secrete the antibiotic as an inactive precursor.

C. They lack the target of the antibiotic.

D. There is no need to resist the effects of the antibiotic.

D. There is no need to resist the effects of the antibiotic.

Several different approaches are used by various species to avoid susceptibility to antibiotics they produce. For example, penicillin-producing fungi lack peptidoglycan cell walls and S. griseus synthesizes an inactive precursor of streptomycin that is activated extracellularly.

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The figure below shows which form of antibiotic resistance?

Choose one:

A. Destroying the antibiotic

B. Transporting the antibiotic out of the cell

C. Modifying the target of the antibiotic

D. Modifying the antibiotic

B. Transporting the antibiotic out of the cell

The figure shows the envelope-spanning efflux pump, which removes the antibiotic from the cell.


What makes multidrug efflux pumps such a dangerous resistance mechanism?
Choose one:

A. While they are limited to very few pathogens right now, the potential from spread is high.

B. They are low energy systems so are inexpensive to the bacterium.

C. They are found naturally in non-pathogenic strains so will appear in emerging diseases.

D. They can export a wide range of antibiotics almost regardless of structure.

D. They can export a wide range of antibiotics almost regardless of structure.

Multidrug efflux pumps are found in many important pathogens and appear to arise readily from mutation of ABC transporters as seen in Mycobacterium tuberculosis. They require energy input but export a very wide range of antibiotics.


Antibiotic resistance in bacteria
Choose one:

A. may be enhanced by inappropriate use in livestock feed.

B. only occurs via acquiring resistance genes from other organisms.

C. does not have any negative impact on the bacteria.

D. is not a problem in developed countries.

A. may be enhanced by inappropriate use in livestock feed.

Promiscuous use of antibiotics selects for antibiotic-resistant bacteria. Bacteria containing antibiotic-resistance mechanisms may grow more slowly than sensitive bacteria in nondrug environments. Antibiotic resistance is a problem throughout the world. Bacteria can become antibiotic resistant by acquiring resistance genes from other organisms or through de novo mutations.


The best potential drug targets are bacterial proteins that are
Choose one:

A. required for growth in vivo.

B. only required for growth of bacteria in laboratory media.

C. not required for growth in vitro or in vivo.

D. similar to host proteins.

A. required for growth in vivo.

The best potential drugs targets are proteins that are required for growth in vivo. Ideally, these will be dissimilar from host proteins to allow for selective toxicity.