New chromogenic identification and detection of Staphylococcus aureus and methicillin-resistant S. aureus

This paper describes a new chromogenic plate medium, CHROMagar Staph aureus (CHROMagar, Paris, France), for the identification of Staphylococcus aureu s on the basis of colony pigmentation. The abilities of CHROMagar Staph aur eus, thermostable nuclease (DNase), and mannitol salt agar (MSA) to Identif y S. aureus isolates (n = 114) and discriminate between S, aureus and coagu lase-negative staphylococci (CoNS; a 22) were compared. CHROMagar Staph aur eus proved to be more sensitive and specific than DNase and MSA, allowing a reliable, simple, and rapid method for the identification of S. aureus iso lates. All CoNS encountered in this study with the exception of S. chromoge nes could be easily differentiated from S. aureus on this medium. The suppl ementation with 4 mu g of oxacillin or methicillin per mi allowed simple id entification of methicillin resistance in hospital-acquired S. aureus strai ns which show multiple-drug resistance profiles. Community-acquired methici llin-resistant S. aureus strains showing non-multi-drug resistance profiles require further evaluation on this new chromogenic medium. Methicillin or oxacillin resistance of all S. aureus isolates was confirmed by the detecti on of penicillin-binding protein 2a, encoded by the mecA gene, using the la tex slide agglutination MRSA-Screen test (PBP 2' Test, DR900M; Oxoid).