DETERMINATION OF MICS FOR STAPHYLOCOCCI USING THE API ATB QUINOLONE AND API ATB MACROLIDE SYSTEMS

The determination of minimal inhibitory concentrations (MICs) is cumbe rsome, but remains necessary in certain cases. We tested the two ATB M IC experimental strips (Biomerieux SA), of which each contains 4 antim icrobials of the same class. These strips can be read automatically. T he MIC quinolone strip contains nalidixic acid, pefloxacin, ofloxacin and ciprofloxacin, whereas the MIC macrolide (lincosamide-streptogrami n) strip contains erythromycin, clindamycin, lincomycin, and pristinam ycin. In order to evaluate these strips, 102 S. aureus and 63 coagulas e negative staphylococci were used. Correlation coefficients for these MICs (mug/ml) and disk diffusion inhibition zone diameters (mm) were nalidixic acid -0.59, pefloxacin -0.95, ofloxacin -0.95, ciprofloxacin -0.91, erythromycin -0.98, clindamycin -0.96, lincomycin -0.96, and p ristinamycin -0.64. Using the Biomic system (Giles Scientific USA), th e same zone diameters were converted to MICs (mug/ml). Rates of agreem ent (+/- 1 dilution) between ATB MICs and Biomic MICs were nalidixic a cid 96 p. cent, ciprofloxacin 98 p. cent, erythromycin 99 p. cent and clindamycin 98 p. cent. Rates of agreement between MICs for the same s trains determined using agar dilution and ATB MICs were nalidixic acid 93 p. cent, pefloxacin 100 p. cent, ciprofloxacin 99 p. cent, ofloxac in 94 p. cent and erythromycin 96 p. cent. The ATB MIC strips are an e asy-to-use tool for MIC determination and their composition is well-su ited to the study of phenotypic resistance and detection of low-level resistance.