[Comparison of three selective chromogenic media for Methicillin-Resistant Staphylococcus aureus detection]

Rapid detection of Methicillin-Resistant Staphylococcus aureus (MRSA) is of major importance in hospital hygiene. In order to reduce the response time from screening laboratories, new selective chromogenic media have been developed and marketed by major microbiology companies. In this context, an evaluation of their performances was needed.

Media produced by Bio-Rad Laboratories (MRSASelect), Becton Dickinson (CHROMagar MRSA) and bioMérieux (chromID MRSA) were studied by 203screening samples, 110 of which were MRSA positive. Each Stahylococcus aureus was identified by catalase detection, Staphytect Plus Dryspot latex agglutination test and free coagulase detection, in addition to mannitol fermentation and Voges-Proskauer tests in the case of doubtful identification. Resistance was verified by checking the inhibition zone diameter of under 20 mm on 30 microg cefoxitin disks.

Bio-Rad Laboratories, Becton Dickinson and bioMérieux media read at 24 or 24/48 hours have a respective sensitivity of 91, 71 and 85/92%. The specificity of these media is 99, 100 and 99/93%.

These media proved to be new powerful and rapid tools used in screening for MRSA detection. MRSASelect is one of the most effective media showing high sensitivity and specificity and the easiest interpretation. chromID MRSA exhibits similar performance but needs more time to be as effective as Bio-Rad media while CHROMagar MRSA isn't enough efficient with its slightly lack of sensitivity to perform a reliable screening.