A Longitudinal Molecular Epidemiologic Study of Methicillin-resistant Staphylococcus aureus (MRSA) Isolates from a University Hospital

Lee, Jin Soo; Park, Ok; Woo, Heung Jung; Jung, Hee Jin; Kim, Woo Joo; Kim, Min Ja; Park, Seung Chull

Abstract

BACKGROUND: Methicillin-resistant Staphylococcus aureus (MRSA) is one of the important nosocomial pathogens and establishs the endemicity within many large hospitals in Korea. The identification and eradication of infection source is essential to prevent and control the spread of MRSA infection. So it is necessary to know how many MRSA clones have existed and how these clones have changed. The aim of this study is to determine the molecular epidemiology of MRSA over a 8-years period from 1991 to 1998 by using pulsed-field gel electrophoresis (PFGE) typing method in a university hospital. METHODS: MRSA isolates from various clinical specimens were collected during 8 years from 1991 to 1998 in Korea University Guro Hospital. The identification of S. aureus was done by catalase and coagulase test. Methicillin resistance was tested by oxacillin disk diffusion method. Pulsed field gel electrophoresis (PFGE) using SmaI was performed for molecular typing. We determined the clonality of MRSA strains by dendrogam analysis. RESULTS: One hundred four MRSA isolates were collected from clinical specimens. PFGE typing showed 8 types and 13 subtypes totally. Type A and type B were the major clonal strains, which comprized of 41.3% (43 strains) and 37.5% (39 strains), respectively, and other types were isolated in small numbers. In 1991, type A and type B were encountered in 36.8% (7/19) each, respectively. In 1994, type A was 65.2% (15/23) and type B was 21.7% (5/23). In 1998, type A was 75.0%(18/24) and type B was 4.2%(1/24). Total types and subtypes according to years were 4 types and 6 subtypes in 1991, 5 types and 6 subtypes in 1992, 4 types and 4 subtypes in 1993, 4 types and 6 subtypes in 1994 and 4 types and 7 subtypes in 1998, respectively. CONCLUSION: The diversity of MRSA strains were observed over 8 years. Type A and type B have been isolated as dominant clones in a university hospital during 8 years. It is presumed that they have isolated from clinical specimens continuously and established the endemicity in this hospital. So it is necessary to prevent the spread of dominant clones intensively, to study the difference of virulence between the dominant and minor clones, and to determine the introduction and spread of MRSA from the community and other hospitals. The PFGE technique was a useful epidemiologic tool for tracking and typing the MRSA isolates.