Performance of MRSA ID chromogenic medium for detection of methicillin-resistant Staphylococcus aureus directly from blood cultures and clinical specimens.

MRSA ID was evaluated to see its performance in identifying methicillin-resistant Staphylococcus aureus (MRSA) directly from blood culture bottles (n = 837), wound swabs (n = 112), and abscesses (n = 18). Each positive blood culture and clinical specimen was directly inoculated on MRSA ID and the culture media routinely used. The sensitivity of MRSA ID was 97.8% after 24 h and 100% after 48 h for blood cultures, and 88.9% after 24 h and 100% after 48 h for wound samples. The specificity was 99.7% after 24 h and 99.6% after 48 h for blood cultures, and 100% after 24 and 48 h for wound samples. Four strains with green colonies indicating MRSA on MRSA ID were identified as methicillin-susceptible S. aureus (MSSA) by conventional methods. Three of these MSSA strains showed negative results with the mecA polymerase chain reaction, and 1 strain harbored the mecA gene. Using MRSA ID with primary culture media should decrease the time (18-24 h) to report a positive result compared with conventional methods.