Antimicrobial susceptibility and molecular characterization of community-acquired methicillin-resistant Staphylococcus aureus.

Community-acquired methicillin-resistant Staphylococcus aureus (MRSA) infections are increasing. Since most published data are on nosocomial MRSA, our goal was to identify the antimicrobial susceptibility profile and resistance mechanisms of pretreatment MRSA isolates obtained from adult subjects participating in recent clinical treatment trials of community respiratory infections. Out of 465 S. aureus isolates, 43 were identified as MRSA. Antimicrobial susceptibility testing indicated susceptibility rates to: vancomycin (100%), gentamicin (86%), clindamycin (39%), quinolones (49%), and erythromycin (12%). Among our MRSA isolates, the MLS constitutive phenotype and ermA were more prevalent than the MLS inducible phenotype and ermC. No isolates had ermB or msrA. All ciprofloxacin resistant isolates had an amino acid change in GyrA and GrlA. The relatedness of our MRSA strains was assessed by ribotyping. Our results indicate that MRSA from adult subjects with community respiratory infections have similar antimicrobial susceptibility profiles and resistance mechanisms as nosocomial MRSA, and represent a genetically diverse group.