How does the Kirby-Bauer assay measure the susceptibility of an antibiotic?

How does the Kirby-Bauer assay measure the susceptibility of an antibiotic?

In Kirby-Bauer testing, bacteria are placed on a plate of solid growth medium and wafers of antibiotics (white disks, shown) are added to the plate. Therefore, the more sensitive the bacteria are to a given antibiotic, the larger the clear bacteria-free zone that forms around the disk containing that antibiotic.

What conclusion can you draw by looking at these Kirby-Bauer results quizlet?

What conclusion can you draw by looking at these Kirby-Bauer results? – The antibiotics tested here appear to be more effective against gram-positive organisms. (There are several discs on the E. coli plate (gram-negative) that do not have clear zones, indicating resistance to those antibiotics.

What is special about Mueller-Hinton agar?

Mueller-Hinton has a few properties that make it excellent for antibiotic use. Starch is known to absorb toxins released from bacteria, so that they cannot interfere with the antibiotics. Second, it is a loose agar. This allows for better diffusion of the antibiotics than most other plates.

What does a big zone of inhibition mean?

Large zones of inhibition indicate that the organism is susceptible, while small or no zone of inhibition indicateresistance. An interpretation of intermediate is given for zones which fall between the accepted cutoffs for the other interpretations.

Is Zone of Inhibition good?

Zone of inhibition testing is fast and inexpensive relative to other laboratory tests for antimicrobial activity. Zone of inhibition testing is especially well suited for determining (albeit qualitatively) the ability of water-soluble antimicrobials to inhibit the growth of microorganisms.

Are bacteria alive in the zone of inhibition?

You are correct that the bacteria may not be dead in the zone of inhibition or at the MIC concentration. If the antibiotic is static, not cidal, they may simply not have grown.

Why is it called zone of inhibition?

If an antibiotic stops the bacteria from growing or kills the bacteria, there will be an area around the disk where the bacteria have not grown enough to be visible. This is called a zone of inhibition.

How does Zone of Inhibition work?

The zone of inhibition is a uniformly circular zone of no bacterial growth around the antibiotic disk. The larger this zone is, the more sensitive the bacteria is to that antibiotic. The smaller the zone is, the more resistant (and, thus, less sensitive) the bacteria is.

What factors influence the size of the zone of inhibition for antimicrobial quizlet?

What factors influence the size of the zone of inhibition for an antibiotic? Diffusion of the antibiotic, the size of the inoculum, the type of medium, and resistance mechanism of organism.

What are the factors considered in the standardization of the antibiotics sensitivity test?

The main factors thought to affect reproducibility of susceptibility testing include inoculum, media composition and depth, delay between application of the disc and incubation, temperature, atmosphere and duration of incubation, generation time, the antibiotic concentration of the disc and the method of reading zone …

What is acquired antibiotic resistance?

Acquired antimicrobial resistance is the result of an evolutionary process by which microorganisms adapt to antibiotics through several mechanisms including alteration of drug target by mutations and horizontal transfer of novel/foreign genes, referred to as resistance genes.