DNA Fingerprinting of Methicillin-Resistant Staphylococcus Aureus by Pulsed-Field Gel Electrophoresis (PFGE): Comparison of Strains from 2 Malaysian Hospitals

A Norazah, SM Liew, AGM Kamel, YT Koh, VKE Lim
Correspondence: Dr A Norazah

ABSTRACT
Aim of Study To determine and compare the pulsed-field gel electrophoresis (PFGE) patterns of endemic MRSA strains in 2 major Malaysian hospitals and to compare the PFGE patterns with antibiotypes of the strains studied.
Methods Fifty-six MRSA strains selected randomly between September 1997 and July 1998 from Hospital Queen Elizabeth (HQE) and Hospital Umum Sarawak (HUS) were tested for antimicrobial resistance and DNA fingerprinting was carried out by pulsed-field gel electrophoresis (PFGE) technique.
Results Seven PFGE types were recognised (A, B, C, D, E and F). All 7 PFGE types were observed in HQE while only 2 PFGE types (B, C) were noted in HUS strains. There is a predominance of a single PFGE pattern (type B) in both hospitals, as seen in 46% of HQE strains and 89% of HUS strains. Subtype B2 was the commonest subtype in HQE while subtype B1 predominated in HUS. Strains resistant to fusidic acid and rifampicin exhibited PFGE type F that is unique to HQE. All strains were resistant to penicillin, erythromycin, cotrimoxazole, tetracycline and gentamicin. Strains with the same antibiotic susceptibility pattern can be different PFGE types.
Conclusion Molecular typing of the MRSA by PFGE is a useful tool in the study of endemic strains present in an institution. Strains in HQE were found to be more heterogeneous than HUS strains. Common PFGE types can also be seen in both hospitals suggesting that some of the strains was genetically related and has propagated within and between the 2 hospitals. Our findings also indicate that the relationship between antibiotic susceptibility and PFGE patterns was not close and antibiograms should not be relied upon for typing strains in epidemiological studies. By knowing the DNA fingerprints of the isolates endemic in each hospital, the spread of MRSA with a particular PFGE type can be monitored within and between hospitals.

Keywords: DNA fingerprinting, MRSA, PFGE, Malaysia
Singapore Med J 2001; 42(1): 15-19