Molecular characterization of methicillin resistant staphylococcus aureus strains isolated from Kerala

Abstract

Staphylococcus aureus is a pathogen of major concern because of its ability to cause a diverse array of diseases ranging from minor infections to life threatening septicemia and its ability to adapt to adverse environmental conditions. The first description of penicillinase-producing strains of S. aureus was published in 1944 (Kirby WMM, 1944). Within a few years, most hospital isolates were resistant to penicillin (Barber M, 1948). Within two years of introduction of methicillin into therapy, S. aureus strains resistant to methicillin were detected. The increase in frequency of MRSA as the causative agent of nosocomial infection and the possibility of emergence of resistance to vancomycin demands quick and trustworthy characterization of isolates and an investigation of clonal spreading within hospitals. This would help to generate enough information topermit the implementation of appropriate measures for the control of these infections. In India the prevalence and spread of MRSA has been recognized late which led to its emergence as a real threat to community and hospital settings. Prevalence of MRSA has widely been reported in several parts of India where MRSA has become a major nosocomial pathogen and few states have even reported the emergence of VISA and VRSA strains. Studies on MRSA have been conducted in all most all the Southern states except Kerala where no such reports are available so far. So we have undertaken this study to determine the antimicrobial susceptibility pattern and the molecular characteristics of MRSA obtained in Kerala. A collection of 104 methicillin resistant Staphylococcus aureus strains were obtained from pus samples randomly from hospitalised patients and out patients from various hospitals in Kerala during the period from Jan 2006 to Jun 2009 and were processed using standard microbiological methods. Antimicrobial susceptibility testing was performed in Mueller Hinton agar plate according to CLSI standards. The central resistance determinants viz. mecA, femA and femB genes were isolated and sequence analysed. Epidemiological typing of the isolates was carried out using phage typing. Molecular typing by Cassette chromosome typing and pulsed field gel electrophoresis was carried out using standard procedures. Microsatellite marker studies were conducted to analyse the clonal diversity of the strains.