# P-1749. Fluconazole disk diffusion on CHROMagar Candida Plus for differentiation between C. auris and C. parapsilosis

## TL;DR

A new method using fluconazole disk diffusion on a specific agar helps distinguish between two types of Candida yeast, which is important for proper infection control.

## Contribution

A rapid and low-resource method for differentiating C. auris from C. parapsilosis using fluconazole disk diffusion and colony coloration is proposed.

## Key findings

- Fluconazole disk diffusion on CHROMagar Candida Plus showed high agreement with broth microdilution for both species.
- A 10 mm zone diameter cutoff provided 91% sensitivity and 90% specificity for differentiation.
- C. auris colonies displayed a turquoise reverse-side coloration on CHROMagar Candida Plus after 48 hours.

## Abstract

Candida auris is an emerging, multidrug-resistant yeast requiring strict contact precautions for colonized or infected patients, posing a significant public health threat. Accurate and timely differentiation of C. auris from C. parapsilosis is crucial, as C. parapsilosis typically does not necessitate such precautions and exhibits greater fluconazole susceptibility. However, distinguishing these species on CHROMagar Candida Plus, a common culture medium, can be challenging. This study evaluated fluconazole disk diffusion on CHROMagar Candida Plus as a rapid, potentially resource-sparing method for differentiating C. auris from C. parapsilosis, particularly in low-resource settings before definitive taxonomic confirmation.

In vitro testing was performed using clinical isolates of C. auris and C. parapsilosis. Antifungal susceptibility was assessed via broth microdilution and disk diffusion with varying fluconazole concentrations on both CHROMagar Candida Plus and RPMI agar. Colony color was also recorded.

High categorical agreement between fluconazole disk diffusion on CHROMagar Candida Plus and broth microdilution was observed for both species. A 10 mm zone diameter cutoff on CHROMagar Candida Plus with a 50 µg/ml fluconazole disk yielded 91% sensitivity and 90% specificity in differentiating the two species. A distinct turquoise coloration was noted on the reverse side of C. auris colonies on CHROMagar Candida Plus after 48 hours.

Fluconazole disk diffusion on CHROMagar Candida Plus, combined with the observation of a turquoise reverse-side colony coloration, demonstrates promise as a readily implementable and potentially low-resource tool for the accurate and timely presumptive differentiation of C. auris and C. parapsilosis in clinical laboratories, particularly before definitive taxonomic confirmation.

All Authors: No reported disclosures