Final answer:
The diffusion bioassay specifically determines the concentration of antimicrobial necessary to inhibit growth of a bacteria (MIC) and can also be used to determine the concentration necessary to kill the bacteria (MBC).
Step-by-step explanation:
The diffusion bioassay is a method used to determine the concentration of antimicrobial necessary to inhibit growth of a bacteria, which is known as the Minimum Inhibitory Concentration (MIC), and to a lesser extent, used to determine the Minimum Bactericidal Concentration (MBC) - the lowest drug concentration that kills ≥99.9% of the starting inoculum. This method involves a series of dilutions of the antimicrobial agent in broth, which is then inoculated with a bacterial strain. The MIC is the lowest drug concentration that prevents visible growth, observed as a lack of turbidity. To determine the MBC, tubes showing no visible growth are subcultured onto agar without antibiotic to observe the lowest concentration that prevents bacterial survival.
The Kirby-Bauer disk diffusion test, another commonly used assay, is designed more to determine the susceptibility of a microorganism to various antimicrobial drugs rather than specify concentrations. However, unlike the diffusion bioassay intended for MIC determination, the Kirby-Bauer test is limited in providing information about drug potency and cannot differentiate between bactericidal and bacteriostatic activities. Instead, it is useful in creating antibiograms for monitoring resistance/susceptibility trends.