Phenotypic and genotypic characterization of MRSA isolated from health care workers in tertiary care hospital.

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) is a significant public health concern, particularly in healthcare settings where healthcare workers (HCWs) act as reservoirs. The aim of this study was to evaluate various phenotypic methods for detection of MRSA among HCWs and study molecular epidemiology of the MRSA isolates by SCCmec typing.

METHODS

A total of 368 nasal swabs were collected from HCWs to study MRSA carriage. Samples were cultured on 5 % sheep blood agar and CHROMagar™ MRSA. Antimicrobial susceptibility was performed using disc diffusion and MIC was determined for select antibiotics as per CLSI guidelines. PCR was performed for detection of mecA, mecC and SCCmec typing. Performance of phenotypic test: oxacillin, cefoxitin (MIC μg/ml) and cefoxitin disc diffusion (DD) was evaluated for detection of MRSA.

RESULTS

Colonization with S. aureus and MRSA (mecA positive) was detected among 65 (17.7 %) and 27 (7.3 %) HCWs respectively. CHROMagar™ MRSA correctly identified 24/27 isolates positive for mecA gene. Among MRSA isolates MDR was high. High level resistance to mupirocin was not detected. Cefoxitin DD was a reliable phenotypic test for MRSA detection showing 100 % sensitivity and specificity. Very major errors (25.9 %) were observed with oxacillin MIC. SCCmec typeV (66.6 %) was the most prevalent, followed by SCCmec IV. SCCmec type I-III, associated with hospital-acquired MRSA (HA-MRSA) were not detected.

CONCLUSION

The significant MRSA carriage rate (7.3 %) among HCWs underscores the need for screening HCWs. CHROMagar MRSA can be used for rapid screening of HCWs and patients for implementing early decolonization and infection control practices. Results from phenotypic test indicate that cefoxitin disc is a reliable method for detection of MRSA. The high prevalence of SCCmec type V in hospital settings is a concern as CA-MRSA strains tend to be more virulent and easily transmissible compared to traditional HA-MRSA.