Amphotericin B, fluconazole, and caspofungin are currently the three antifungal agents most commonly used to treat candidemia and invasive candidiasis. This practice is supported by FDA approval and the most recent Infectious Diseases Society of America guidelines . While all these agents have been used effectively in clinical studies, these studies included mostly patients with C. albicans infections; thus their efficacy against NAC is not necessarily universal or well known. In vitro study has shown decreased susceptibility to amphotericin B in isolates of C. famata, C. guilliermondii, C. inconspicua, C. kefyr, C. krusei, C. lusitaniae, and C. rugosa and to fluconazole in isolates of C. famata, C. firmetaria, C. guilliermondii, C. inconspicua, C. krusei, and C. lusitaniae [7, 8]. The MICs of caspofungin have been demonstrated to be higher in C. famata, C. guilliermondii, and C. parapsilosis isolates . The number of antifungal agents available continues to increase in the setting of a shift of candidal infections to those caused by non-albicans species. Because of this, identification to species and increased use of susceptibility testing has become necessary to appropriately select which agent to use .
CHROMagar Candida is a chromogenic medium that is advertised as able to identify C. albicans, C. krusei, and C. tropicalis. With the increasing incidence of human disease being produced by the less common Candida species, we were interested in testing the performance of this medium with the less common agents of candidiasis. We found, as previously reported, that most of these rarer Candida species and C. parapsilosis produced typical convex, creamy yeast colonies in shades of pink, lavender, and less commonly ivory, not distinguishable from each other (and often not consistent between isolates of the same species). C. parapsilosis, one of the most commonly recovered NAC, produced the widest range of colors and morphologies, making it impossible to identify using this medium.
Many of the rare NAC produced morphology and colors similar to those seen with C. krusei on this medium. We found individual isolates of C. lipolytica and C. norvegensis, many isolates of C. firmetaria, and all tested C. inconspicua were indistinguishable from C. krusei. Some that were distinguishable, produced similar color as that of C. krusei, with the pale border, but with waxy colonies. Most of these species share reduced susceptibility to fluconazole that is common with C. krusei.
We confirmed our previous observation that C. rugosa appears to typically produce a readily identifiable and unique color/colony type on CaC [12, 22]. Eleven of 15 isolates of this organism produced the same light blue-green color and a colonial morphology similar to that of C. krusei. C. rugosa has been shown in clinical reports and by in vitro testing to be less susceptible to amphotericin B [7, 8, 23]. Rapid identification of this NAC is of great importance to allow provision of appropriate therapy to patients.
As previously reported by our group and others, this study did find C. glabrata to be readily distinguishable from other species that produced pink to lavender colonies on CaC. With the use of larger numbers of isolates, we again noted that this species produced smaller colonies starting out as dark pink hues, becoming dark violet with time, commonly with a small diffusion of dark violet pigment into the surrounding agar and a thin pale border [12, 22]. This was most apparent after prolonged incubation (72 hours) at the lower temperature suggested by the manufacturer (30°C), or after 48 hours when incubated at 37°C.
Our readers could not distinguish C. dubliniensis from C. albicans when observed in a blinded fashion. The isolates we tested were somewhat darker, especially at the higher incubation temperature, but this was only obvious when CaC culture was performed in parallel to C. albicans controls. The report by Kirkpatrick et al.  that made the initial observation that C. dubliniensis produce darker green colonies with CaC did this with primary isolation of clinical materials onto the medium. Our isolates were not from primary samples and thus may have been affected by storage conditions and repeated subculturing. Odds and Davidson reported that they could differentiate C. dubliniensis from C. albicans using stored isolates, but this was best shown after 72 hours of incubation at 37°C .