Chapter 13: Antimicrobial Susceptibility Testing Flashcards
(32 cards)
What is the primary purpose of antimicrobial susceptibility testing?
To determine which antimicrobial agents might be effective in treating infections
Performed on bacteria isolated from clinical specimens.
What are the traditional methods of susceptibility testing?
Standard disk diffusion or dilution methods
Commercial manual or automated antimicrobial susceptibility test systems are alternatives.
What organization publishes standards for antimicrobial susceptibility testing?
Clinical and Laboratory Standards Institute (CLSI)
Worldwide International Organization for Standardization (ISO) standards are also used.
What is the significance of epidemiological cut-off values (ECV)?
Helps identify emerging resistance
Important for monitoring antimicrobial susceptibility trends.
What factors should be considered in susceptibility testing?
- Body site from which the organism was isolated
- Presence of other bacteria and specimen quality
- Host status (immunocompromised, allergies)
Pure culture is generally preferred.
Who is involved in selecting antimicrobials for testing?
- Medical technologists
- Pharmacists
- Physicians
This selection is crucial for effective treatment.
What is the maximum number of disks that can be placed on a 150mm plate?
12 disks
Plate size constraints limit the number of antimicrobials tested.
What is the minimum inhibitory concentration (MIC)?
Lowest concentration of antimicrobial agent required to inhibit the growth of a bacterial isolate
MIC is a key measure in susceptibility testing.
What is the minimum bacteriocidal concentration (MBC)?
Concentration that does not show growth when plated
MBC is used to determine the bactericidal effect of an antimicrobial.
What is the Kirby Bauer test?
A disk diffusion method used to assess antimicrobial susceptibility
Involves swabbing an agar plate and measuring zones of inhibition.
What must be controlled during disk diffusion testing?
- Disk storage conditions
- Agar depth (3 to 5 mm)
- pH (7.2 to 7.4)
These factors ensure accurate susceptibility results.
What is an antibiogram?
The overall antimicrobial susceptibility profile of a bacterial isolate to a battery of antimicrobial agents
Important for guiding empirical therapy.
What are cumulative antibiograms used for?
Analysis of individual susceptibility results to guide physicians in empirical therapy
They help identify trends in antimicrobial resistance.
What should be done if an atypical antibiogram is found?
- Reexamine the disk diffusion plate
- Check earlier reports
- Repeat the test if necessary
Verification ensures accuracy in susceptibility results.
What is the purpose of using McFarland turbidity standards?
To standardize the number of bacteria for susceptibility testing
Ensures accurate concentration for reliable results.
What are the primary objectives in reporting susceptibility test results?
- Least toxic
- Most cost-effective
- Most clinically appropriate agent
Avoiding broad spectrum agents helps prevent resistance.
What conditions can affect the selection of antimicrobial drugs for testing?
- Patient population
- Allergies
- Drug interactions in pediatric patients
Consideration of these factors is crucial for patient safety.
What is the role of automated antimicrobial susceptibility test methods?
To provide rapid and accurate results in susceptibility testing
Examples include BD Phoenix System and VITEK 2.
What are the limitations of agar dilution methods?
- Short shelf life of plates
- Labor-intensive
Despite limitations, agar dilution is still used for certain organisms.
What is the significance of selecting an antimicrobial test method?
Flexibility, cost-effectiveness, need for quantitative information, and speed
These factors influence the choice of method in clinical settings.
What is an antibiogram?
A summary of the susceptibility of bacteria to various antibiotics
It is used to guide treatment decisions in infections.
What are common challenges of susceptibility testing of biofilms?
Challenges include:
* Antimicrobial penetration of the biofilm
* Exposure to higher concentrations of inhibitory substances
* Need for a broad spectrum of activity
* Differences in the microenvironment
* Differential rate of growth of bacteria
* Trapping of the antimicrobial by exopolymers
* Issues with differential diffusion
* Exposure to by-products of microbial growth
* Release of antimicrobial inhibitory factors by killed bacteria
These challenges complicate the effectiveness of antimicrobial treatments.
What factors should be considered when selecting an antimicrobial test method?
Factors include:
* Flexibility of method
* Cost-effectiveness
* Need for quantitative information on MICs
* Speed
These factors can significantly influence the choice of testing method.
What is the Minimum Bactericidal Concentration (MBC) Test?
A test important for immunocompromised patients, performed in conjunction with MIC tests.
It determines the lowest concentration of an antimicrobial that kills 99.9% of the bacteria.
