Micro-Media Systems anaerobe panel versus broth disk method in anaerobe antimicrobial testing

Frozen microtitration trays manufactured by Micro-Media Systems (MMS) for antimicrobial testing of anaerobic bacteria were evaluated and compared with the broth disk elution method of Virginia Polytechnic Institute (VPI) described by Wilkins and Thiel. A total of 224 clinical anaerobic isolates were tested. Susceptibility results were compared for carbenicillin, cefoxitin, chloramphenicol, clindamycin, penicillin, and tetracycline. Published procedures for the MMS and VPI methods were followed using aerobic inoculation. Growth performance in the MMS method was 74% compared with 89% in the VPI method. For each antibiotic, the MMS minimum inhibitory concentration was compared with the VPI test concentration. Of the 972 drug-organism combinations, 2.9% of the results were discrepant. Clindamycin and tetracycline accounted for 82% of the discrepancies. The MMS anaerobe susceptibility panels were easy to inoculate and interpret and compared well with the VPI broth disk susceptibility method.