Molecular Epidemiology of Methicillin-resistant Staphylococcus aureus Outbreak by Plasmid Restriction Analysis

Lee, Mi Ae; Kang, Eun Sook; Hong, Ki Sook; Chung, Wha Soon

Abstract

BACKGROUND: Methicillin-resistant Staphylococcus aureus (MRSA) continues to be a major cause of nosocomial infection and a molecular typing is necessary for proper epidemiologic investigations of sources and moles of spread in an outbreak. An nosocomial outbreak of MRSA in a neonatal intensive care unit at Ewha Womans University Mokdong Hospital was suspected. To investigate the clonality of isolates and control the spread of nosocomial outbreak, we performed plasmid restriction analysis of MRSA isolates from patients and medical staffs.
METHODS
We studied 7 MRSA strains (umbilicus 4, blood 1, urine 1 and pus 1) from patients in a neonatal intensive care unit and the MRSA strains from nares and hands surveillance cultures of 26 medical staffs (4 medical doctors and 22 nurses). All MRSA strains were tested for antimicrobial susceptibility and plasmic analysis after EcoRI restriction. We analyzed the plasmid patterns of MRSA isolated from patients and compared with those from medical staffs.
RESULTS
Ten MRSA strains (from 7 nares and 3 hands) were isolated from surveillance cultures of 26 medical staffs. Seven out of 10 MRSA strains from medical staffs revealed identical pattern of antibiogram which was the same pattern in all 7 MRSA strains from seven patients. Plasmid restriction patterns were classified 6 groups from A to F showing 2-10 bands. Six out of 7 MRSA strains from the patients showed group A(A1 5, A31) and 5 out of 10 MRSA strains from the medical staffs showed group A(A1 1, A21, A32, A41) and remainders showed different plasmid restriction analysis patterns.
CONCLUSIONS
These results suggest that plasmid restriction analysis is a rapid, inexpensive, and good discriminating molecular typing of MRSA outbreak and is useful for the epidemiologic investigation of MRSA outbreaks in the clinical laboratory.