Isolation and molecular characterization of methicillin-resistant coagulase-negative staphylococci from nasal flora of healthy humans at three community institutions in Rio de Janeiro City

We describe the isolation and molecular characterization of methicillin-res istant coagulase-negative staphylococci (MRCNS) from the nasal flora of hea lthy humans from three institutions located in Rio de Janeiro City. Swabs w ere obtained from the nares of students attending a non-residential public school and adults from two military quarters. Isolates of staphylococci wer e tested for the presence of the mecA gene by hybridization with a specific probe. S. epidermidis was the most frequent MRCNS (38 of the total 45 CNS isolated). Twenty-five percent of nasal staphylococcal carriers studied wer e colonized with MRCNS. Pulsed-field gel electrophoresis (PFGE) of SmaI-dig ested genomic DNA was carried out to study the clonality of the methicillin -resistant S. epidermidis (MRSE) isolates. In addition to cross-colonizatio n among individuals belonging to the same institution, familial cross-colon ization appeared to contribute to the spread of the methicillin-resistant i solates among two inter-communicable institutions. Indeed, the wide genomic diversity among the MRSE flora suggests that the spread of the mecA gene a mong these isolates might also have occurred via horizontal transmission. D espite the limited number of institutions analysed, it is reasonable to con clude that our data do not represent a situation unique to the three organi zations but may reflect other communities in Rio with respect to transmissi on of MRCNS.