BACTE LAB - L3

Antimicrobial Susceptibility Test

A method of susceptibility which has been standardized primarily for testing of rapidly growing bacteria either fastidious or non-fastidious organism

To test the effectiveness of antibiotics

What is the primary clinical purpose of performing antimicrobial susceptibility testing (AST)

Kirby-Bauer

A standard diffusions procedure with filter-paper disc on agar, is frequently used to determine the drug susceptibility of microorganisms isolated from infectious processes

Kirby-Bauer

This method allows the rapid determination of the efficacy of a drug measuring the diameter of the zone of inhibition that results from diffusion of the agent into the medium surrounding the disk

1.5 × 8^8 CFU/mL

What approximately concentration of microorganisms does a bacterial suspension matching a 0.5 McFarland standard contain?

0.08 - 0.1

When measuring the optical density of a 0.5 McFarland standard, what is the expected absorbance range read at 60 nm?

Mueller-Hinton Agar

Which standard culture medium is globally recommended for performing routine disk diffusion Antimicrobial Susceptibility Testing (AST)?

within 15 minutes

Within how many minutes of preparation must be the standardized bacterial suspension be applied to the Mueller-Hinton Agar?

35 •C

What is the recommended incubation temperature for Mueller-Hinton agar plates in the Kirby-Bauer test?

16-18 Hours

What is the standard incubation time duration for Kirby-Bauer AST plates?

Too light

what is the status of the inoculum concentration if individual colonies are apparent instead of the expected confluent lawn of growth?

12 disks

What is the maximum number of antimicrobial disks recommended on a large 150 × 15 mm Mueller Hinton Agar plate?

6 disks

What is the maximum number of antimicrobial disks recommended on a small 100 mm Mueller-Hinton Agar plate?

the drug begins diffusing immediately upon touching the moist agar

Why should an antimicrobial disk should not be relocated once it comes into contact with the agar surface?

Sliding calipers

What instrument is specifically used to measure the diameters of the zones of complete inhibition during a Kirby-Bauer test?

Clinical and Laboratory Standards Institute

What organization publishes the authoritative document “Performance Standards for Antimicrobial Susceptibility Testing (M100)”?

Agar Cup Diffusion

Employs boring holes on the agar, while streaking of inoculum to the agar is done in an overlapping manner / lawn technique

Agar-Cylinder Diffusion

Make use of metal or plastic cylinder to contain the solutions for research purposes

E-Test

Test that uses a strip and allows direct reading of the exact MIC where the zone of inhibition intersects

Minimum Inhibitory Concentration

The lowest concentration of an antibiotic that completely prevents visible bacterial growth?

Minimum Bactericidal Concentration

The lowest concentration of an antibiotic that kills > 99.9% of the initial bacterial population?

96 well microplates

What plate format is characteristic of the broth microdilutions test method?

Two-fold antibiotic dilutions

In standard 96-well microplate layout for broth microdilution, what is typically contained in Column 1-10?

Growth Control

In standard 96-well microplate layout for broth microdilution, what is typically contained in Column 11?

Sterility Conteol

In standard 96-well microplate layout for broth microdilution, what is typically contained in Column 12?

Subculture from tubes/well

How is MBC determined after finding the MIC in broth dilution?

Intermediate

The uncertain response; may be effective at higher doses?

Resistant

The infection is unlikely to respond to standard dosing of the antimicrobial agent?

Susceptible

The infection is likely to respond to standard dosing of the antimicrobial agent?

60 degree angle

When streaking the inoculum onto a Mueller-Hinton agar plate during Kirby-Bauer testing, how should the swab be angled across the plate surface?