BACKGROUND: Selective chromogenic media allowing one-step meticillin-resistant 
Staphylococcus aureus (MRSA) isolation and identification are widely used. 
However, the changing epidemiology of MRSA means that the suitability of these 
chromogenic media requires investigation.
AIM: To evaluate the following chromogenic media - Colorex MRSA, MRSA Select II, 
ChromID MRSA, and MRSA Brilliance 2 - for the detection of divergent strain 
types.
METHODS: We used a diverse collection of S. aureus, including strains harbouring 
the mecC gene, strains expressing varying levels of meticillin resistance, and 
isolates recovered from patient samples.
FINDINGS: MRSA Select II, Colorex MRSA, and ChromID each grew at a density of 
1.5 × 10(1)cfu/mL for each SCCmec type investigated. Brilliance 2 demonstrated 
growth at 1.5 × 10(1)cfu/mL for mecC MRSA but at a higher density (1.5 × 
10(4)cfu/mL) for the three mecA MRSA strains. All four media demonstrated 
excellent sensitivity for MRSA detection (≥99%), but reduced levels of 
specificity (85-73%) when challenged with a range of meticillin-susceptible S. 
aureus (MSSA) isolates. High levels of false positives (∼50%) were also obtained 
with all chromogenic media when tested with mec-negative borderline 
oxacillin-resistant S. aureus (BORSA) isolates.
CONCLUSION: Although false positives may be obtained with some strains of MSSA 
and BORSA, the high sensitivity of these media and their ability to recover 
almost all MRSA tested (including oxacillin-susceptible and mecC-positive 
strains) confirm the value of chromogenic agar in MRSA detection.