BBL CHROMagar Staph aureus is superior to mannitol salt for detection of Staphylococcus aureus in complex mixed infections.

We used 200 sputum specimens from patients with cystic fibrosis to evaluate BBL CHROMagar Staph aureus medium (CSA; BD Diagnostics, Spark, MD). Samples were inoculated to CSA, trypticase soy blood agar (BA), and Mannitol Salt (MS; BD Diagnostics). After 18 hours of incubation, CSA detected 39 (78%) of 50 Staphylococcus aureus (SA) samples; BA detected 30 (60%); and MS detected 29 (58%). Sensitivity after overnight incubation (at least 18 hours) was 82% for CSA, 72% for BA, and 71% for MS. At 2 days, CSA detected 48 (96%) of the SA. There were 2 false-positive results on CSA (99% specificity). There were 4 (8%) minor and no major or very major discrepancies between minimum inhibitory concentration (MIC) results for isolates grown on CSA and those grown on BA. Even at early reading times, CSA was superior to conventional media for detection of SA in these very complex cultures. MICs from all SA samples can be reported 24 hours sooner, and an additional BA subculture is not needed.