Deck 12: Laboratory Methods and Strategies for Antimicrobial Susceptibility Testing

Question 1

The interpretive criteria for categories of susceptible, intermediate, or resistant are based on extensive studies that correlate MIC with

A)serum achievable levels for each antimicrobial agent.
B)particular resistance mechanisms.
C)successful therapeutic outcomes.
D)All of the above are correct.

Answer 1

A
The interpretive categories of MIC-based testing are defined according to the attainable concentrations of the antibiotic in the patient's bloodstream. In order for the antibiotic to be effective, the concentration of the drug in serum must be inhibitory to the bacteria.

Question 2

Enterococcal resistance to ampicillin predicts resistance to

A)vancomycin.
B)aminoglycosides.
C)cephalosporins.
D)amikacin.

Answer 2

C
Ampicillin is a predictor antimicrobial agent use to detect resistance to other derivatives of penicillin-like cephalosporins.

Question 3

Criteria for establishing a bacterial isolate as clinically significant include

A)cultivation of the organism from a clinical specimen.
B)detection and/or the abundance of the organism on direct specimen Gram stain in the presence of white blood cells.
C)predominance of the organism in specimen cultures.
D)its antimicrobial susceptibility results.

Answer 3

B
Not all bacteria found in a clinical specimen are clinically significant. Normal resident flora may even be predominant, especially in improperly collected specimens.

Question 4

Enterococcal high-level gentamicin resistance predicts resistance to

A)vancomycin.
B)aminoglycosides.
C)cephalosporins.
D)amikacin.

Question 5

The decision to perform susceptibility testing depends on

A)the clinical significance of a bacterial isolate.
B)the predictability of a bacterial isolate's susceptibility to the antimicrobial agents most commonly used against them.
C)availability of reliable standardized methods for testing the isolate.
D)All of the above are correct.

Question 6

In the microdilution broth dilution method, the interpretive criteria for the susceptible, intermediate, or resistant categories are based on

A)the amount of turbidity in the test well.
B)correlations of MIC with serum achievable levels for the antimicrobial agent, particular resistance mechanisms, and successful therapeutic outcomes.
C)the size of the zone of inhibition.
D)the reciprocal of the MIC value.

Question 7

The primary goal of antimicrobial susceptibility testing is to

A)determine whether the pathogen is capable of expressing resistance to the potential choices of antimicrobial agents.
B)determine the extent of an organism's intrinsic resistance.
C)determine in vivo whether the administered antibiotic is killing the pathogen.
D)All of the above are correct.

Question 8

The serum bactericidal test (SBT) involves

A)subculturing the clear tubes of a completed broth dilution test.
B)99.9% reduction in CFU/mL compared with the organism concentration in the original inoculum.
C)using patient serum to detect bacteriostatic and bactericidal activity and the antibacterial impact of factors other than the antibiotics.
D)All of the above are correct.

Question 9

Staphylococcal resistance to oxacillin is used to determine and report resistance to

A)vancomycin.
B)aminoglycosides.
C)cephalosporins.
D)amikacin.

Question 10

Chromogenic cephalosporins are used to test for

A)the action of beta-lactamase inhibitors.
B)intrinsic resistance to beta-lactam drugs by decreased intracellular uptake of the drug.
C)the production of beta-lactamase by the infecting organism.
D)intrinsic resistance to beta-lactam drugs by altered antibiotic targets.

Question 11

In the disk diffusion method of antimicrobial susceptibility testing, what is the standard agar base medium for testing most bacterial organisms?

A)5% blood agar
B)Mueller-Hinton agar
C)Mueller-Hinton broth
D)Brain heart infusion broth
E)Any of the above can be used.

Question 12

Growth on the oxacillin agar screen means that a patient should be treated with

A)oxacillin.
B)methicillin.
C)vancomycin.
D)cephalosporins.
E)chloramphenicol.

Question 13

An important factor that plays a key role in a patient's outcome in an infectious disease that is not taken into account by susceptibility testing is

A)antibiotic diffusion in tissues and host cells.
B)serum protein binding of antimicrobial agents.
C)drug interactions and interference.
D)status of patient defense and immune systems.
E)All of the above are correct.

Question 14

Up-to-date tables that list potential antimicrobial agents to include in batteries for testing against particular organisms or organism groups is published by

A)CDC (Centers for Disease Control and Prevention).
B)NCCLS (National Committee for Clinical Laboratory Standards).
C)MSOP (Manual of Standard Operating Procedures).
D)CLSI (Clinical and Laboratory Standards Institute).

Question 15

Detection of the haze produced by some resistant staphylococci and enterococci against methicillin and vancomycin can best be accomplished by

A)using reflected light.
B)using transmitted light.
C)placing the medium under the light rather than in front of it.
D)microscopy.

Question 16

An important requirement for appropriate inoculum preparation in susceptibility testing includes

A)use of a pure culture.
B)use of an inoculum that matches the severity of the infection.
C)use of a single isolated colony.
D)use of a variety of colony types.

Question 17

A haze of bacterial growth within a more clearly defined zone of inhibition may be observed when testing

A)aminoglycosides.
B)sulfonamides.
C)penicillins.
D)cephalosporins.
E)All of the above are correct.

Question 18

The MIC result recorded in antimicrobial testing can be defined as

A)the maximum concentration of antimicrobial agent that should be used for optimal therapy.
B)the minimum concentration of antimicrobial agent that should be used for optimal therapy.
C)the lowest antimicrobial agent concentration that completely inhibits visible bacterial growth.
D)the highest antimicrobial agent concentration that completely inhibits visible bacterial growth.

Question 19

The minimal bactericidal concentration (MBC) test involves

A)a continuation of the procedure for conventional broth dilution testing.
B)subculturing the clear tubes of a completed broth dilution test.
C)99.9% reduction in CFU/mL compared with the organism concentration in the original inoculum.
D)All of the above are correct.

Question 20

The concentrations in a broth dilution test that separate the categories of susceptible, intermediate, and resistant are called

A)minimum inhibitory concentrations.
B)tolerance limits.
C)breakpoints.
D)border concentrations.

Question 21

Bactericidal tests should be performed

A)for every clinically significant organism isolated from a clinical specimen.
B)to evaluate antimicrobials usually considered to be bacteriostatic.
C)for severe and life-threatening infections.
D)All of the above are correct.

Question 22

The difference between the serum bactericidal test and the minimum bactericidal concentration test is that

A)the medium used is patient's serum.
B)the source of the antibiotic used in testing is the patient's own serum that contains the therapeutic antimicrobial agent(s) that the patient has been receiving.
C)the antibacterial impact of factors other than the antibiotics also are observed.
D)All of the above are correct.