[Evaluation of inoculum density prepared by prompt inoculation system and antimicrobial susceptibility test results by the automated MicroScan WalkAway system].

The Prompt Inoculation System adapted to the susceptibility testing by the automated microbiology system, MicroScan WalkAway (Dade MicroScan Inc., West Sacramento, CA, U.S.A.) was evaluated by determining colony forming units (cfu) per ml of the inocula and by the susceptibility test results obtained through repeated testing of the American Type Culture Collection (ATCC) reference strains described by the National Committee for Clinical Laboratory Standards (NCCLS). The colony forming units per ml of the inocula prepared by the Prompt ranged 2x10++(5) to 2x10(6)++ cfu/ml for the ATCC reference strains, the results indicating that the Prompt gave a higher inoculum density and was more reproducible when compared to the standard turbidity, McFarland adjustment. Also, most inocula prepared from the clinical isolates, comprising the strains of Enterobacteriaceae,no-entericbacilli,staphylococci,enterococci, and streptococci,contained 1x10(6) to 3x10(6) cfu/ml. Although the inocula prepared by the Prompt contained more viable bacterial cells, the outcome results for susceptibility testing by the MicroScan WalkAway were highly acceptable. Four ATCC reference strains were repeatedly tested. Of 540 MIC determinations, 489 (90. 6%) were within the acceptable MIC ranges described by the NCCLS M100-S9, whereas the inocula prepared by the photometric adjustment gave 87.4%. In conclusion, the Prompt inocula were found to give more precise susceptibility test results mostly equivalent to those obtained from inocula prepared by the conventional photometric procedures.