Proposed MIC quality control guidelines for National Committee for Clinical Laboratory Standards susceptibility tests using seven veterinary antimicrobial agents: ceftiofur, enrofloxacin, florfenicol, penicillin G-novobiocin, pirlimycin, premafloxacin, and spectinomycin.

The present multicenter study proposes broth microdilution quality control (QC) ranges for the antimicrobial agents ceftiofur, enrofloxacin, florfenicol, penicillin G-novobiocin, pirlimycin, premafloxacin, and spectinomycin, which are used in veterinary practice. Six separate laboratories tested replicates of National Committee for Clinical Laboratory Standards (NCCLS)-recommended QC organisms (Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, Staphylococcus aureus ATCC 29213, and Enterococcus faecalis ATCC 29212) on medium lots both common and unique to all laboratories. The proposed ranges were within 3 or 4 log2 dilution steps of the modal MICs for all organism-antimicrobial agent pairs, depending on their MIC distributions. With > or = 94.7% of all MIC results being within the proposed QC ranges, all combinations tested comply with NCCLS guidelines and all have been accepted by the NCCLS subcommittee developing susceptibility testing procedures for veterinary laboratories.