This is a walk-through of Minimum InhibitoryConcentration, MIC:This tray has 8 rows, 4 for Staphylococcus aureus (SA) and 4 forMethicillin-Resistant S. aureus (MRSA). Each row has 12compartments, or wells. The wells have differentconcentrations (ug/ml) of the antibiotic Oxacillin in them. FromLeft to Right, the concentration of Oxacillin is goingdownacillin concentration, pg/ml64 32 16 8421 0.5 0.25 0.13 0.06 0SAdnThe same amount of S. aureus broth culture is added to eachwell and the tray is incubated. A color change shows that S.aureus grew in a given well.MRSAWhat is the lowest concentration at which SA is inhibited (doesnot grow)?64mg/mlWhat is the lowest concentration at which MRSA is inhibited?What is the MIC for Oxacillin vs SA?What is the MIC for Oxacillin vs MRSA?- NotesComments33°F

Minimum Inhibitory Concentration (MIC) assay is used to determine the minimum concentration of an antimicrobial agent required to stop the visible growth of a microorganism. MIC assays tells us the inhibitory effect and not the biocidal effect as the absence of visible growth can be due to either inhibition or killing of the microbe by the antimicrobial agent , which is hard to differentiate here.Here the 12 wells (columns ) have serially diluted volumes of antimicrobial agent or inhibitor. The concentration of inhibitor reduces to half as we move from left to right . i.e. the concentration of oxacillin decreases from 2X to X in every successive well left to right. The concentration does not change vertically (up or down ) within the same well(column). The concentration only halves in horizontal direction from left to right. "From left to right the concentration of oxacillin is going 2X to X down and 2X to X up." A clear solution solutions indicates the concentration of microbes did not increase from their concentration that was inoculated into each sample i.e. complete inhibition. Here the concentration of right most well with a clear solution is the MIC (as concentration of oxacillin decreases from left to right) Lowest concentration at which SA got inhibited is 0.5μg/ml Lowest concentration at which MRSA got inhibited is 32μg/ml MIC for oxacillin v/s SA =0.5μg/ml MIC for oxacillin v/s MRSA=32μg/ml