Methicillin resistant Staphylococcus aureus (MRSA) is a major cause of nosocomial and life threatening infections worldwide. Screening of high risk populations for MRSA colonisation can assist in reducing MRSA transmission within hospitals. Culturing MRSA screening swabs onto selective and differential chromogenic MRSA media has been shown to be a rapid and cost effective method in aiding the prevention and control of MRSA in healthcare settings .
In this study we evaluated the BBL™ CHROMagar™ MRSA II and the bioMerieux ChromID® MRSA media using a panel of 48 genetically diverse MRSA strains previously characterised by the Australian Collaborating Centre for Enterococcus and Staphylococcus Species (ACCESS) Typing and Research. The oxacillin minimum inhibitory concentrations of the isolates ranged from 1 to >256mg/L. In addition ten methicillin susceptible Staphylococcus aureus (MSSA) and 2 coliforms, were tested. Chromogenic media plates were inoculated with 1μl of approximately 104 and 107 organisms per ml of each isolate, and incubated aerobically at 35oC for twenty hours.
All 48 MRSA isolates grew on both chromogenic media (sensitivity 100%) and none of the MSSA or coliforms were isolated (specificity 100%). Growth performance of some of the MRSA isolates varied, with one isolate (MIC >256 mg/L) and seven isolates (MIC 6 - >256 mg/L) performing better on the BBL™ CHROMagar™ MRSA II and the bioMerieux ChromID® MRSA media respectively
In conclusion the BBL™ CHROMagar™ MRSA II and the bioMerieux ChromID® MRSA media are able to grow a range of genetically diverse MRSA. The choice of which media should be used by a laboratory may depend upon the MRSA strains isolated within the region.