Evaluation of a colorimetric method for detecting amphotericin B-resistant Candida isolates

Substitution of Antibiotic Medium 3 for RPMI 1640 in the microdilution variant of M27-A has been proven to permit detection of amphotericin B-resistant Candida isolates. For this purpose, we have studied the utility of the colorimetric indicator alamarBlue to simplify the former process because it is a readily available commercial system. When used in combination with the NCCLS-recommended RPMI 1640, alamarBlue did not improve the ability of RPMI 1640 to detect resistant isolates. When used in combination with Antibiotic Medium 3, alamarBlue reduced discrimination between susceptible and resistant isolates by increasing the MIC of susceptible isolates. Thus, alamarBlue does not improve detection of amphotericin B resistance among Candida isolates.