The requirements of a living system include:
A. raw materials and energy.
B. catalysis of reactions.
C. a selective barrier.
D. biological information.
E. All of these choices are correct.
The scientist who developed a system of identifying the variety of strains of streptococci was
A. Hans Zimmer.
B. Donald Sutherland.
C. O. T. Avery.
D. Rebecca Lancefield.
Why are nucleoside analogs active only against replicating viruses?
A. These drugs can only be taken up by cells that are infected by viruses. They are shut out from non-infected cells. This makes them effective only against cells where viruses are replicating.
B. Each of these drugs is specifically activated by enzymes produced by the viruses. The viruses will only produce these enzymes when they are replicating, so the drugs can only become activated when these processes are occurring.
C. Nucleoside analogs work by directly inhibiting the activity of nucleic acid polymerases. If the virus isn't actively replicating, there's no DNA/RNA polymerase active for the drug to inhibit, so the drug cannot work.
D. Nucleoside analogs work by being incorporated into growing strands of DNA/RNA. This indirectly shuts down further extension of these chains. However, new strands of viral DNA/RNA are only being created when the virus is replicating. As such, these drugs can only work when the virus is actively replicating as well.
Explain how using a combination of two antimicrobial drugs helps prevent the development of spontaneously resistant mutants.
A. All drugs work synergistically with each other-that is, their combined effects are far greater than either could achieve individually. Two drugs together helps to eliminate microbes, even if they have developed spontaneous mutations that would confer upon them resistance to the drugs.
B.
It is highly unlikely that the microbe might spontaneously develop two specific mutations to resist the effects of a pair of drugs. As such, even if one drug is resisted by the microbe, the second drug will eliminate the mutated microbe, thus preventing the development of spontaneously resistant mutants overall.
C. All drugs work antagonistically with each other-that is, their combined effects are far greater than either could achieve individually. Two drugs together helps to eliminate microbes, even if they have developed spontaneous mutations that would confer upon them resistance to the drugs.
D. Drugs can also select for mutations that will enhance the activity of another drug. So, each of the paired drugs will help to select for spontaneous mutations that enhance the activity of the other drug in the pair.
Why would it be important for the Kirby-Bauer disc diffusion test to use a standard concentration (number of cells in the sample) of each of the bacterial strains being tested?
A. Antibiotics only work within a narrow range of cell concentrations. If you use a concentration that is too low or too high, you will get inaccurate measurements of the zone of inhibition.
B.
Antibiotic resistance is usually only manifested by bacteria that have achieved a very high concentration (i.e., they are in the very end of the stationary phase of the growth curve). It's important to use bacteria specifically at this particular point for disc diffusion testing.
C.
If you were to use one strain that was stationary phase (high concentration, replicating very slowly or not at all), and another strain that was just beginning log phase (low concentration but replicating quickly), you could see dramatically different results in the disc diffusion test. This could skew your interpretations of resistance/susceptibility.
D. Growth on the Mueller-Hinton agar plates utilized is very sensitive to the phase of the growth curve the bacteria are in when they are placed on the plate. If they are not in the log phase when they are placed on the plate, they will not grow and the test will be worthless.
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