Comparison of four commercial microdilution systems for susceptibility testing of anaerobic bacteria

The reliability of four commercially available broth microdilution systems (ATB ANA, MHK-Anaerob-Biotest, Dynatech MIC system, Sceptor Anaerobe MIC system) for routine susceptibility testing was evaluated using agar dilution and broth macrodilution as reference methods. Using the categories "susceptible", "moderately susceptible" and "resistant", the rate of essential agreement (complete agreement plus minor errors) of all four systems compared to the two reference methods was satisfactory, ranging from 93% (Dynatech system and agar dilution) to 98% (Sceptor system and agar dilution). The rate of complete agreement compared to the agar dilution and broth dilution method respectively was 61% and 60% for the MHK-Anaerob-Biotest, 65% and 63% for the Dynatech system, 72% and 72% for ATB ANA, and 85% and 80% for the Sceptor system. The Sceptor system was thus superior to the other systems. The systems were easy to operate and inoculate, although arrangement of antimicrobial agents in the Dynatech panels was apt to be confusing.