Evaluation of the antimicrobial susceptibilities of coagulase-negative staphylococci by E-test.

Coagulase-negative staphylococci (CoNS) have recently emerged as important nosocomial pathogens. In this study, the susceptibility of 53 isolates of CoNS (42 S. epidermidis, 6 S. haemolyticus, 3 S. caprae, 1 S. lugdunensis and 1 S. chromogenes) obtained over a 1 year period at a Brazilian Hospital were tested for vancomycin, teicoplanin, cephalothin, penicillin, oxacillin, and chloramphenicol. The minimal inhibitory concentration (MICs) were determined by the E-test using saturated swabs or the flooding method. No isolates showed resistance to vancomycin, 3 (5.7%) were resistant to teicoplanin, 5 (9.4%) to cephalotin, most of them, (47, 88.6%) were resistant to penicillin, 19 (35.8%) to oxacillin and 27 (50.9%) to chloramphenicol. The study shows that the increased resistance of CoNS can cause serious infections of difficult treatment. The E-test proved to be a convenient and reliable method for MIC determination of CoNS isolates and the qualitative and quantitative results obtained by flooding were much more reproducible than the results obtained using swabs.