CHROMagar Candida Medium for Direct Susceptibility Testing of Yeast from Blood Cultures

Abstract

An evaluation was performed on 95 blood cultures positive for Candida spp. to determine the correlation of direct susceptibility testing of fluconazole versus both standardized disk diffusion and MIC methods. For direct testing, an aliquot taken from BD BACTEC Plus and/or BD BACTEC Lytic/10 bottles (Becton Dickinson [BD], Sparks, MD) positive by gram stain for yeast was subcultured to CHROMagar Candida (BD), and a 25-g fluconazole disk (BD) was placed on the plate. The area of growth inhibition surrounding the disk was measured at 24 and 48 h. In addition, a subculture of the isolate was tested by a microdilution MIC using YeastOne (TREK Diagnostics Systems Inc., OH) and disk diffusion (NCCLS M44-A) using a standardized inoculum plated onto CHROMagar Candida as well as Mueller-Hinton agar to which 2% glucose and 0.5 g/ ml methylene blue dye was added (MH-GMB). The categorical interpretation derived from the MIC was used as the reference to which the disk diffusion results were compared. There were a total of 41 Candida albicans, 23 Candida glabrata, 20 Candida parapsilosis, 9 Candida tropicalis, and 1 each of Candida krusei and Candida lusitaniae tested. At 24 h there was full agreement among the methods for all C. albicans, C. tropicalis, C. lusitaniae, and C. krusei isolates. For the C. parapsilosis isolates at 24 h there was one very major discrepancy using the direct CHROMagar and one major error with the standardized MH-GMB. The majority of the errors were seen at 24 h with the C. glabrata isolates. Of the 23 C. glabrata isolates at 24 h by direct CHROMagar, there were 10 minor and 1 very major error; by MH-GMB there were 12 minor and 2 very major errors; and by standardized CHROMagar Candida there were 13 minor and 2 major errors. There were no very major errors with C. glabrata when all plates were read at 48 h. At 24 h by the direct and standardized CHROMagar the majority of C. glabrata isolates were more resistant, whereas by MH-GMB they were more susceptible than the reference MIC interpretation. In summary, subculturing yeast directly from blood cultures onto CHROMagar to which a fluconazole disk has been added may provide a presumptive identification at 24 h and, with the exception of C. glabrata, was able to predict the susceptibility to fluconazole with the majority of Candida isolates examined in this evaluation.Over the past decade there has been more interest and subsequently progress in developing reliable methods for the susceptibility testing of yeast. In particular, testing Candida species against azole antifungal agents has provided valuable information for treatment of patients with invasive yeast infections. However, even with the advent of standardized guidelines for microdilution methods, testing is not readily available for a majority of laboratories due to the expense and labor that are inherent in the method (5, 6). Recently, guidelines for testing by disk diffusion have been published (7). This method utilizes a medium and a procedure that are familiar to the vast majority of labora...

Invasive Fungal Infections and Approaches to Their Diagnosis

“…Specimens that may be contaminated with bacteria should also be cultured on a selective medium such as inhibitory mould agar, SABHI, or BHI plus antibacterial agents (e.g., gentamicin, chloramphenicol, or ciprofloxacin plus streptomycin). CHROMagar (Hardy Diagnostics; Becton-Dickinson) is a chromogenic medium that is both selective for fungi and differential for certain Candida species (Murray, Zinchuk, & Larone, 2005;Odds & Bernaerts, 1994;Pfaller, Houston, & Coffman, 1996;Tan & Peterson, 2005). This medium inhibits bacterial growth and because different species of Candida appear as different coloured colonies it is useful in detecting mixed cultures of Candida and other fungi (Odds & Bernaerts, 1994;Pfaller et al, 1996).…”

Agreement of Direct Antifungal Susceptibility Testing from Positive Blood Culture Bottles with the Conventional Method for Candida Species

“…Only one study has previously evaluated the use of fluconazole disks for direct susceptibility testing of Candida species; however, that study used CHROMagar, which is not a recommended susceptibility testing medium (26). Another approach has been the direct inoculation of Vitek antifungal cards for susceptibility testing.…”

Interpretive Breakpoints for Fluconazole and Candida Revisited: a Blueprint for the Future of Antifungal Susceptibility Testing

“…Furthermore, physicians felt reassured in continuing patients on fluconazole if the MIC demonstrated susceptibility of the Candida isolate. On the other hand, detection of resistance to fluconazole is clearly desirable, and early recognition of resistance in clinical isolates may contribute to successful clinical and microbiologic outcomes (86,101,112). Hadley et al (28) reported the use of real-time antifungal susceptibility testing in modifying treatment decisions in several patients with invasive fungal infections.…”

“…The simplicity and flexibility of disk diffusion testing makes it a very appealing method for use in the clinical laboratory (72,74,75). Results are clearly available in real time (i.e., 24 h), and innovative efforts to integrate this form of antifungal testing into the work flow of the clinical laboratory are ongoing (101). Thus, fluconazole disk diffusion testing is being performed in clinical laboratories throughout the world as an aid in selecting the most efficacious, nontoxic, and costeffective therapy for treatment of candidiasis.…”