Strain relatedness of endemic MRSA isolates in a burns unit in South India--a five year study

Methicillin-resistant Staphylococcus aureus (MRSA) is an important hospital-acquired pathogen in healthcare centres worldwide. The strain characteristics vary widely from country to country, although some strains have the propensity to spread globally. E-MRSA 15 and 16 have been established as epidemic strains in the UK and Europe. MRSA is widely prevalent in the Indian sub-continent and is endemic in the Burns Unit of St Johns Medical College Hospital, Bangalore, India. The purpose of the study was to investigate the predominance of one or more epidemic strains within an endemic situation. A representative selection of 65 isolates of MRSA over a period spanning five years (1994-1998) was subjected to antibiogram comparison, phage-typing and pulsed field gel electrophoresis (PFGE) using SmaI. The antibiogram comparison was not a discerning method of strain discrimination. At least 11 different phage-types were seen among these 65 isolates; 35.4% belonged to phage-types A and SM-A. PFGE studies showed 12 distinct patterns, with a single pattern accounting for over half of the isolates. The study showed that the isolates from India were diverse and distinct from strains of MRSA such as E-MRSA reported from many studies in the UK. Molecular characterization of isolates is a source of valuable information that could enhance global surveillance; more work is needed across the Indian sub-continent to establish the nature of MRSA strain diversity.