Evaluation of anaerobic microdilution MIC results with the Prompt Inoculation System

The Prompt Inoculation System (3M Co.) was compared with the overnight suspension inoculation procedure used with a broth microdilution anaerobic commercial system (Micro-Media Systems) for differences in MIC. MIC results from both suspension methods using six National Committee for Clinical Laboratory Standards-recommended quality control organisms were identical in 18 instances (75%) and within +/- 1 log2 dilution in 96% of the comparisons. Results with 45 anaerobic clinical isolates also compared satisfactorily; 83% of the results were identical and 97% were within +/- 1 log2 dilution. In addition, the direct (Prompt)-inoculated microdilution trays produced better growth and more valid MIC results; 92% of the clinical isolates produced MIC results versus 79% by the overnight suspension procedure.