Performance of the Chromogenic Medium CHROMagar Staph Aureus and the Staphychrom Coagulase Test in the Detection and Identification of Staphylococcus aureus in Clinical Specimens

CHROMagar Staph aureus (CSAM) (CHROMagar Microbiology, Paris, France) is a new chromogenic medium designed to enable detection of colonies of Staphylococcus aureus by their pink color. A total of 775 specimens were cultured in parallel on CHROMagar Staph aureus and conventional media. Among the 267 S. aureus strains recovered on at least one medium, 263 were isolated on CSAM medium (sensitivity, 98.5%), and 245 (sensitivity, 91.8%) were isolated on conventional media. The specificity of presumptive identification of S. aureus on the basis of pink colony color on CSAM medium was 97% (493 of 508). This specificity increased to 100% when coagulase detection with the Staphychrom coagulase test was added and to 98.8% when S. aureus surface components were detected by agglutination in the Pastorex Staph Plus test. Susceptibility testing of 67 S. aureus strains, performed in parallel on pink CSAM colonies and on colonies grown on blood agar, gave similar results. Thus, rapid and accurate recognition and identification of S. aureus isolates were achieved with CSAM as the primary isolation medium, followed by the staphylocoagulase Staphychrom test. Antimicrobial susceptibility testing (disk-diffusion method or ATB STAPH System) can be performed directly on pink CSAM colonies. Staphylococcus aureus causes severe suppurative infections associated with high morbidity and mortality. Its isolation from a patient with an infectious syndrome usually leads to specific antibiotic treatment. S. aureus can be missed when the clinical specimen contains a mixed flora. This is especially the case when other staphylococcal species with an identical colony appearance are present or when swarming colonies of Proteus or Pseudomonas cover those of S. aureus. Misidentification of S. aureus in a clinical sample can have serious clinical repercussions. S. aureus colonies grown on a chromogenic medium, such as CHROMagar Staph aureus (CHROMagar Microbiology, Paris, France) (CSAM) are pink, unlike colonies of other Staphylococcus species. CSAM has been reported to yield a higher detection rate for S. aureus in plurimicrobial samples. The reported sensitivity of the CSAM method is 95.5%, com