In the Kirby-Bauer susceptibility test, the 0.5 McFarland nephelometer standard is used to?

In the Kirby-Bauer susceptibility test, the 0.5 McFarland standard serves as a reference to adjust the turbidity of the inoculum. This standard corresponds to a specific concentration of bacterial cells, approximately 1.5 x 10^8 CFU/mL. By matching the turbidity of the bacterial suspension to the 0.5 McFarland standard, researchers ensure that the inoculum is consistent and accurate, which is crucial for interpreting the results of the susceptibility test.

Having a uniform inoculum is vital because variations in bacterial density can lead to unreliable results in determining the susceptibility of the bacteria to the antibiotic being tested. If the inoculum is too dense, antibiotics may appear less effective, while a too-dilute suspension could make bacteria seem more susceptible than they really are.

Although the other options relate to different aspects of the testing process, they do not directly pertain to the primary purpose of the 0.5 McFarland standard, which focuses strictly on achieving proper inoculum turbidity.