Molecular Characterization of Methicillin Resistant Staphylococcus aureus Strains Isolated in Kerala, South India

The aim of the present study is to report the prevalence, antimicrobial susceptibility pattern molecular characteristics of methicillin resistant Staphylococcus aureus strains and the emergence of vancomycin intermediate Staphylococcus aureus (VISA) strains in Kerala, India. The study was conducted during January 2006 to December 2007 on 70 strains obtained from pus cultures of patients from various hospitals in Kerala, India. Organisms were isolated, cultured and identified as per standard routine procedures. Susceptibilities to thirteen commonly used antibiotics were tested by agar diffusion method as recommended by CLSI. Minimum inhibitory concentrations of oxacillin, ciprofloxacin and vancomycin were determined using standard protocol. Plasmid profile analysis of the strains carried out and the central resistance determinant mecA and internal control gene femA were isolated and sequenced. Cassette chromosome typing carried out as per standard procedures. Among the 70 strains isolated 13 of them showed reduced susceptibility to vancomycin and two isolates were resistant. All the strains were resistant to oxacillin and ampicillin and uniformly sensitive to gentamycin. mecA gene was isolated from 88% strains and sequence analyzed. The strains were found to be Hospital Associated-MRSA (HA-MRSA) with type III cassette chromosome. This study reveals the high prevalence of MRSA and a gradual emergence of VISA strains in Kerala. This is greatly due to the irrational and overuse of antibiotics like vancomycin and partly due to negligence on the part of health care workers in acknowledging the prevalence of MRSA and VISA strains and initiating appropriate strategies to control their spread. Careful use of existing antibiotics and regular monitoring of strains circulating in a particular hospital at regular intervals is necessary to control the spread of multidrug resistant strains and to prevent the emergence of even more serious strains.