Antibiotic Susceptibility Testing of Anaerobes: Comparison of Three Methods, Including an Automated Micro‐method, and Evaluation of the Effect of Different Media

Disc‐diffusion, agar‐dilution and microdilution methods were compared for testing the antibiotic sensitivity of anaerobic bacteria. Eight antibiotics and 31 test organisms were used. There was a poor correlation between MIC values obtained by the agar‐dilution and microdilution procedures. The test organisms showed an apparently increased sensitivity to the antibiotics when tested by the agar‐dilution, as compared with the microdilution, procedures. Columbia Blood Agar and Thioglycollate Haemin agar, were evaluated for the disc‐diffusion and agardilution procedures. There was a poor correlation between the MIC values and inhibition zone diameters for the two media, with lower MIC values and larger zones on Thioglycollate Haemin agar.