Comparison of agar dilution, tube dilution, and broth microdilution susceptibility tests for determination of ramoplanin MICs.

Standard broth microdilution (with and without bovine serum albumin [BSA] supplementation), tube dilution, and agar dilution susceptibility tests were compared for determining ramoplanin MICs. With a data base of 246 clinical isolates of gram-positive bacteria from 33 U.S. sites, it was shown that (i) agar and tube dilution susceptibility tests gave essentially the same results (93.9% of the test results were within 1 doubling dilution of equivalence), (ii) broth microdilution susceptibility tests gave results up to 5 doubling dilutions higher than agar or tube assays, and (iii) this data skewing could be reversed by BSA supplementation (final concentration, 0.02%) of the broth microdilution test medium.