Molecular typing and characterization of macrolide, lincosamide and streptogramin resistance in Staphylococcus epidermidis strains isolated in a Mexican hospital.

Staphylococcus epidermidis is a normal commensal of skin that has become a serious clinical problem because of the combination of increased use of intravascular devices and an increasing number of hospitalized immunocompromised patients. In addition, there is a lack of information pertaining to resistance to macrolide, lincosamide and streptogramin type B (MLS(B)) in developing countries, including Mexico. The aim of this study was to investigate the incidence of resistance to MLS(B) antibiotics in isolates of S. epidermidis obtained in the General Hospital of Acapulco in Mexico. Susceptibility to erythromycin, clindamycin and quinupristin-dalfopristin was tested by a diffusion test, and MICs to oxacillin, erythromycin and lincomycin were determined. Differentiation between MLS(B) phenotypes was performed by a double disc diffusion test. A total of 38 of the 47 strains of S. epidermidis isolated from nosocomial infections were resistant to oxacillin [meticillin-resistant S. epidermidis (MRSE)]. The phenotypes obtained were: 18 constitutive MLS(B), 3 inducible MLS(B), 6 macrolide streptogramin and 4 lincosamide; 7 strains were susceptible to MLS(B) antibiotics. The genes associated with resistance were detected by PCR. Genotyping showed a predominance of the ermA gene followed by genes ermC and msrA. The frequency of the genes detected varied slightly from results that have been reported in isolates from other countries. Clonal types were identified by PFGE and revealed the dissemination of two major clones of MRSE in the Mexican hospital. This is believed to be the first report in Mexico on the genes associated with the MLS(B) resistance phenotype in S. epidermidis, in addition to observing a wide distribution of clonal types in the General Hospital of Acapulco, Mexico.