Restriction endonuclease analysis of plasmid DNA from methicillin-resistant Staphylococcus aureus: clinical application over a three-year period.

OBJECTIVE: To investigate trends in plasmid types of methicillin-resistant Staphylococcus aureus over a 3-year period and determine the clinical impact of plasmid typing. DESIGN: Restriction endonuclease analysis of plasmid DNA (REAP) was used to type 270 clinical isolates. SETTING: A Veterans Affairs Medical Center. RESULTS: Forty-four different REAP types were identified and, of these, 23 appeared only once. Types designed as V1 and V2 were more commonly found in nosocomial cases than in community-acquired cases (p < .05); whereas the K and D types were more common in isolates from community-acquired cases (p < .05). In 30 (11%) isolates, no plasmid was detected. When combined with epidemiological data, REAP typing revealed 4 small outbreaks that would have been missed using traditional epidemiological methods alone. In large outbreaks involving 10 or more cases, REAP typing data revealed unsuspected patterns of transmission. CONCLUSIONS: Multiple plasmid types were present in this endemic setting. Restriction endonuclease analysis of plasmid DNA was a practical and valuable adjunct to traditional epidemiological methods.