Genetic and phenotypic characterisation of clinical methicillin-resistant staphylococcus aureus in a Malaysian hospital / Lim King Ting

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the main bacterial pathogens responsible for a variety of nosocomial infections ranging from soft-tissue infections to bacteremia. Since most MRSA is often resistant to multiple antibiotics, this has raised a concern over the limited choice of antimicrobial-agents for treatment of life-threatening cases. The objectives of this study were to determine the antimicrobial resistance profiles, presence of resistance and virulence genes, to investigate the molecular epidemiology of MRSA and their evolution over a six-year period. The antibiograms of 188 MRSA strains isolated from UMMC were analyzed by disk-diffusion test and minimum inhibitory concentrations. The agr and SCCmec types, presence of resistance and virulence genes were determined by PCR, genetic diversity by PFGE, coa-RFLP, MLST, spa and dru typing and molecular evolution by MLST-spa-dru types. All the strains were sensitive to vancomycin. They showed high resistance (≥80%) towards ciprofloxacin, clindamycin, erythromycin and gentamicin. A significant increase (P<0.05) in resistance rates towards trimethoprim-sulfamethoxazole, netilmicin and tetracycline between 2003 and 2008 was observed. blaZ gene was detected in all strains whereas ermA, aac(6’)-aph(2”), tetM, ermC, tetK, ileS, msrA and mupA specific amplicons were detected in 157(84%), 156(83%), 92(49%), 40(21%), 39(21%), 10(5%), 4(2%) and 2(1%) strains, respectively. blaZ, tetM, ermC, tetK, ileS2 and mupA genes were plasmid-encoded. Double mutations in rpoB gene were associated with high rifampicin-resistance while mutational change 461Leu/Lys in fusA gene was associated with high fusidic acid-resistance. The prevalence of sea, sec and ica among strains isolated in 2008 increased significantly (P