Molecular characterisation of methicillin-resistant Staphylococcus aureus (MRSA) from keratitis patients: a microbiological analysis

Background In order to diagnose and characterise a major corneal infection, 'keratitis,' which can lead to blindness, molecular studies were conducted to assess the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) strains in patients suffering from keratitis Methods The selected culture positive for strains of S aureus were subjected to 18 antimicrobial drugs for their sensitivity behaviour, and the minimum inhibitory concentration (MIC) of oxacillin was determined by the microdilution method as recommended by the National Committee for Clinical Laboratory Standards. Further, S strains were characterised using molecular tools. Results Among the 202 cases included in the present study, 64 (31.2%) cases were found to be S aureus-positive, of which only six strains were MRSA. The highest resistance was observed for penicillin (65.6%) which was followed by a significant number of bacterial isolates showing resistance to methicillin (9.3%), while all organisms were susceptible to vancomycin. The minimum inhibitory concentrations of oxacillin for MRSA strains ranged between 16 and 128 mu g/ml. A multiplex PCR assay for Staphylococcal Cassette Chromosome mec complex (SCCmec) of MRSA strains (N = 6) showed that five MRSA strains had a Type III cassette, and one had a Type II cassette. The pulsed field gel electrophoresis of three MRSA strains showed closely related band patterns. Conclusion The close relatedness among bacterial strains as observed by employing different typing techniques suggests that the clonal characteristics of multiresistant MRSA isolates could be deciphered. The presence of Type II SCCmec in keratitis subjects is probably the first report from India, as it has not been reported earlier.