Molecular epidemiologic analysis of Staphylococcus aureus isolated from clinical specimens

Nosocomial infections caused by Staphylococcus aureus are clinically serious and control of such infections requires strain typing to identify the source of contamination. Recently, pulsed-field gel electrophoresis (PFGE) and random amplified polymorphic DNA (RAPD) assay have been introduced and have provided a high level of strain discrimination of S. aureus isolated from clinical specimens. This study was performed to classify 82 strains of S. aureus isolated from 4 hospitals in the Kwangju-Chonnam area by PFGE and RAPD assay. Methicillin-resistant S. aureus (MRSA) was identified by disk diffusion method using the oxacillin disk and polymerase chain reaction of mecA gene was done in 69 strains. Eight-three strains including S. aureus ATCC 25923 were classified into 10 groups by RAPD assay, and into 8 groups by PFGE. Classified groups were not related to area or hospital. Classification was not characteristic between MRSA and methicillin-susceptible strains. Nosocomial infections due to outbreak were suggested because some strains disclosed identical band patterns by PFGE. These results indicate that medical personnels and instruments are routes of nosocomial infections caused by MRSA. PFGE and RAPD assay are powerful tools for the epidemiological study of S. aureus, but PFGE is more effective than RAPD assay. RAPD assay needs optimal combination of primers.