Antimicrobial resistance and persistence of Staphylococcus epidermidis clones in a Brazilian university hospital

Oxacillin is an alternative for the treatment of Staphylococcus spp. infections; however, resistance to this drug has become a major problem over recent decades. The main objective of this study was to epidemiologically characterize coagulase-negative staphylococci (CoNS) strains recovered from blood of patients hospitalized in a Brazilian teaching hospital. Oxacillin resistance was analyzed in 160 strains isolated from blood culture samples by phenotypic methods, detection of the mecA gene, and determination of intermediate sensitivity to vancomycin on brain heart infusion agar supplemented with 4 and 6 μg/mL vancomycin. In addition, characterization of the epidemiological profile by staphylococcal cassette chromosome mec (SCCmec) typing and clonal analysis by pulsed-field gel electrophoresis (PFGE) were performed. The mecA gene was detected in 72.5% of the isolates. Methicillin-resistant CoNS isolates exhibited the highest minimum inhibitory concentrations and multiresistance when compared to methicillin-susceptible CoNS strains. Typing classified 32.8% of the isolates as SCCmec I and 50% as SCCmec III. PFGE typing of the SCCmec III Staphylococcus epidermidis isolates identified 6 clones disseminated in different wards that persisted from 2002 to 2009. The high oxacillin resistance rates found in this study and clonal dissemination in different wards highlight the importance of good practices in nosocomial infection control and of the rational use of antibiotic therapy in order to prevent the dissemination of these clones.