Nosocomial Outbreak of Methicillin-resistant Staphylococcus aureus Analyzed by Molecular Epidemiology

Kim, Jae Seok; Kim, Eui Chong; Ki, Chang Seok; Lee, Nam Yong

Abstract

BACKGROUND
An outbreak of nosocomial infection due to methicillin-resistant Staphylococcus aureus (MRSA) was suspected at Seoul National University Hospital because the isolation rate of MRSA from patients with surgical wounds or other exudates was increased in one month period. To demonstrate the clonality of these isolates, restriction endonuclease analysis of plasmid DNA (REAP) and pulsed-field gel electrophoresis (PFGE) were performed.
METHODS
Among the MRSA isolates in one month period, seventeen MRSA isolates from eleven surgical wound specimens and six other specimens were tested, Six isolates were taken from two patients at various times during hospitalization, Plasmid DNA was isolated by a modification of the alkaline lysis method and digested by EcoRI, The restriction analysis of SmaI-digested chromosomal DNA of MRSA strains was done by PFGE.
RESULTS
Two representative groups were identified among fourteen isolates from ten patients. PFGE analysis showed seven isolates from five patients were of the same group, but REAP showed a different pattern on one isolate. Other seven isolates from five patients were classified as the another same group by PFGE, and they could be divided into five groups by REAP. And the remainders showed different PFGE patterns each other.
CONCLUSIONS
The outbreak strains of this study could be divided into two different groups by PFGE and REAP. Furthermore, one group of the outbreak-related isolates showed entirely identical pattern. by both PFGE and REAP. The combination of more than one molecular epidemiological technique should be performed in order to demonstrate the clonality of the outbreak strains.