Clinical and molecular characteristics of nosocomial meticillin-resistant Staphylococcus aureus skin and soft tissue isolates from three Indian hospitals

Abstract

We analysed risk factors for nosocomial meticillin-resistant Staphylococcus aureus (MRSA) skin and soft tissue infections (SSTIs) in three Indian hospitals. We also determined antimicrobial resistance patterns and genotypic characteristics of MRSA isolates using pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST) and staphylococcal cassette chromosome (SCCmec) typing. Medical records of 709 patients admitted to three tertiary hospitals with nosocomial S. aureus SSTIs were clinically evaluated. Antimicrobial susceptibility testing of patient isolates was performed in accordance with Clinical and Laboratory Standards Institute guidelines, with meticillin and mupirocin resistance confirmed by multiplex polymerase chain reaction. PFGE analysis of 220 MRSA isolates was performed, followed by MLST and SCCmec typing of a selected number of isolates. MRSA was associated with 41%, 31% and 7.5% of infections at the three hospitals, respectively. Multiple logistic regression analysis identified longer duration of hospitalisation [odds ratio (OR): 1.78; OR: 2.83 for >or=20 days], intra-hospital transfer (OR: 1.91), non-infectious skin conditions (3.64), osteomyelitis (2.9), neurological disorders (2.22), aminoglycoside therapy (1.74) and clindamycin therapy (4.73) as independent predictors for MRSA SSTIs. MRSA isolates from all three hospitals were multidrug resistant, with fifteen clones (I-XV) recognised. A majority of the strains possessed type III cassette. The common sequence type (ST) 239 was considered the signature MLST sequence for PFGE clone III. This major MRSA clone III was closely related to the UK EMRSA-1 and was significantly more resistant to antibiotics. Dissemination of multidrug-resistant MRSA clones warrants continuous tracking of resistant genotypes in the Indian subcontinent.