Problems in minimum inhibitory concentration determinations in coryneform organisms. Comparison of an agar dilution and the Etest.

The antimicrobial susceptibility of 159 coryneform organisms was determined by an agar dilution and Etest methods. Overall, the correlation between minimum inhibitory concentrations obtained by both techniques was good (> or = 0.09) for most antibiotics and organisms although the essential agreement ranged from 59% to 88.3%. Most organisms were equally categorized (sensitive, intermediate, or resistant) by both methods with only 0.2%, 0.4%, and 3.5% of very major, major or minor discrepancies, respectively. Such percentages dropped significantly when discrepant strains were retested. The correlation was specially good for Corynebacterium jeikeium and Corynebacterium urealyticum.