Lecture 5 and 6: Antibiotic susceptibility testing

How is drug activity against bacteria quantified in the Kirby-Bauer (disk diffusion) method of susceptibility testing?

Zone of inhibition

How is drug activity against bacteria quantified in the serial dilution method of susceptibility testing?

Minimum inhibitory concentration

What factors make accurate antimicrobial susceptibility testing difficult to perform outside a diagnostic laboratory?

Proper inoculation (pure culture, consistent and current amount), interpretation of inhibition, timing, broth, content

What is a susceptibility breakpoint? What is it used for?

Specific to combination of pathogen, dosing regimen, species, and condition.

Who creates validated veterinary breakpoints? What information is considered in the creation of validated breakpoints?

Created by a committee of experts. Species, pharmokinetics, and dosing are considered in the creation of validated breakpoints

Validated breakpoints are specific for

pathogen, drug, dosing regimen, species affected, and condition (site of infection).

Why might susceptibility breakpoints differ for the same drug/pathogen pairs in the same species but different locations of infection?

Susceptibility testing does not take into account the tissue concentrations and concentration ability in different tissues.

What might diagnostic labs do when they are reporting a test for which there is not a validated veterinary breakpoint?

Will usually list as “no interpretation”

Antimicrobial susceptibility testing is a laboratory-based method used to evaluate what?

a) The color of pathogens

b) The size of pathogens

c) The susceptibility of pathogens to antimicrobial drugs

d) The growth rate of pathogens

c) The susceptibility of pathogens to antimicrobial drugs

What factors are considered during antimicrobial susceptibility testing?

a) Only drug factors

b) Only physiological factors

c) Neither drug nor physiological factors

d) Both drug and physiological factors

d) Both drug and physiological factors

What is a key limitation to remember about susceptibility testing?

a) It always provides a definitive answer

b) It is a prediction of what might happen in a living animal based on a laboratory setting

c) It is always accurate

d) It is inexpensive

b) It is a prediction of what might happen in a living animal based on a laboratory setting

What does the abbreviation MIC stand for?

a) Maximum Inhibition Capacity

b) Minimum Inhibitory Concentration

c) Microbial Interference Compound

d) Macroscopic Identification of Culture

b) Minimum Inhibitory Concentration

What is the importance of quality control in antimicrobial susceptibility testing?

a) It is not important

b) It only affects the cost of testing

c) It is critical for accurate results

d) It only affects the speed of testing

c) It is critical for accurate results

What factors are important for quality control in antimicrobial susceptibility testing?

a) Proper lighting

b) Use of old cultures

c) Proper inoculation and pure culture

d) Variable amounts of bacteria

c) Proper inoculation and pure culture

Why is the drug with the lowest MIC not always the best choice?

a) It is always the best choice

b) It is too expensive

c) Other factors like drug distribution, toxicity, and breakpoints need to be considered

d) It is always unavailable

c) Other factors like drug distribution, toxicity, and breakpoints need to be considered

What do laboratory reports indicate about bacteria?

a) Only the size of the bacteria

b) Only the shape of the bacteria

c) Whether the bacteria are S, I, or R (susceptible, intermediate, or resistant)

d) Only the quantity of bacteria

c) Whether the bacteria are S, I, or R (susceptible, intermediate, or resistant)

What are susceptibility breakpoints based on?

a) Only the pathogen

b) Only the dosing regimen

c) A combination of pathogen, dosing regimen, species, and condition

d) Only the species

c) A combination of pathogen, dosing regimen, species, and condition

What factors are considered when determining susceptibility breakpoints?

a) Species and cost

b) Dosing and availability

c) Species, pharmacokinetics, and dosing

d) Cost and availability

c) Species, pharmacokinetics, and dosing

According to the speaker, what does a breakpoint indicate?

a) the cost of the drug

b) the availability of the drug

c) the interpretation of what happened in the test

d) the accuracy of the test

c) the interpretation of what happened in the test

According to the speaker, what is the committee of experts that determines breakpoints?

a) Veterinary Medicine Association (VMA)

b) American Medical Association (AMA)

c) Clinical Laboratory Standards Institute (CLSI)

d) American Veterinary Medical Association (AVMA)

c) Clinical Laboratory Standards Institute (CLSI)

According to the speaker, for which of the following infection locations would the breakpoint for susceptibility be much higher?

a) Skin

b) Soft Tissue

c) Urinary Tract

d) Lungs

c) Urinary Tract

According to the speaker, what is one reason why the breakpoint for susceptibility is much higher for a urinary tract infection?

a) Because the drug is concentrated in the urine

b) Because the drug is spread throughout the body

c) Because the bacteria is weaker in the urine

d) Because the drug is not effective in the urine

a) Because the drug is concentrated in the urine

According to the speaker, where do macrolides concentrate in the body, making them popular for BRD (Bovine Respiratory Disease)?

a) Urinary Tract

b) Skin

c) Soft Tissue

d) Lungs

d) Lungs

According to the speaker, which of the following should you factor in when picking a drug?

a) Cost

b) Name

c) Color

d) Breakpoint

d) Breakpoint

What does it mean when a lab says "no interpretation possible"?

a) There is definitely a validated breakpoint for the drug.

b) They want to tell you that it is definitely safe to use.

c) They don't have a breakpoint for it.

d) It is always the best choice for treatment.

c) They don't have a breakpoint for it.

According to the speaker, which of the following is more important than the MIC itself?

a) The laboratory's interpretation of whether the drug is susceptible or resistant

b) The color of the drug

c) The cost of the drug

d) The availability of the drug

a) The laboratory's interpretation of whether the drug is susceptible or resistant

According to the speaker, the consideration of drug and physiological factors is important during what type of testing?

a) Pregnancy testing

b) Antimicrobial susceptibility testing

c) Allergy testing

d) Genetic testing

b) Antimicrobial susceptibility testing