Evaluation of ChromID MRSA for the Detection of Methicillin-resistant Staphylococcus aureus

Background: Methicillin-resistant Staphylococcus aureus (MRSA) is a significant pathogen in both nosocomial and community settings, and screening for a carrier is an important infection control practice in many hospitals. We evaluated the sensitivity and specificity of the ChromID MRSA assay (bioMerieux, Marcy I’Etoile, France). Methods: A total of 190 clinical samples were collected from the anterior nares of premature infants in a newborn intensive care unit (N-ICU). Equal volumes (100μL) of the samples were inoculated on mannitol salt agar with oxacillin 6 mg/L (MSAO) and ChromID MRSA after emulsifying the screening swab in brain-heart Infusion broth with oxacillin 6 mg/L (BE). The specimens in BE were subcultured on ChromID MRSA after an overnight incubation. Results: Twenty-one of 190 samples (11%) was positive for MRSA by BE. After a 24 h incubation, the sensitivity/specificity of MSAO was 52%/98% and that of ChromID MRSA was 62%/100%, and at 48 h, the sensitivity/specificity of MSAO was 62%/92% and that of ChromID MRSA was 81%/99%. Conclusion: ChromID MRSA is a useful selective medium for the rapid isolation and identification of MRSA. (Korean J Clin Microbiol 2009;12:169-173)