[Antimicrobial susceptibility and polyclonal dissemination of Staphylococcus aureus strains]

To determine the prevalence ofmethicillin-resistant Staphylococcus aureus (MRSA), its antimicrobial susceptibility patterns and classify strains by pulsed-field gel electrophoresis (PFGE).

106 S. aureus strains isolated from patients hospitalized at the Maracaibo city university hospital, Venezuela, were processed during the first quarter of 2009. The culture, isolation and identification of S. aureus were done by conventional methods. Antimicrobial susceptibility was determined by the disk diffusion method. The presence of mecA gene in MRSA strains was verified using the polymerase chain reaction (PCR).

Fifty-four strains (50.94%) were MRSA and twenty three antibiotypes were detected. The most frequently observed was the one including beta-lactams, macrolides, lincosamides, aminoglycosides and quinolones. There were forty multi-resistant isolates (74.0%) between MRSA strains. All methicillin-resistant isolates were mecA positive. PFGE classified MRSA stains in 50 pulsotypes, each one containing between six and thirteen bands. Four small groups, of two strains each, had 80% of similarity. Five of the eight strains in these small clusters (62.50%) had the same pattern of resistance.

There is a high prevalence of multi-resistant MRSA strains with polyclonal dissemination in the hospital.