Candida auris Screening in a Simple Setup: Introduction, When

Introduction of Candida auris Screening in a Simple Setup

Table of Contents

Candida auris Screening in a Simple Setup is possible to presumptively identify Candida auris in a simple laboratory setup, though definitive identification typically requires advanced methods. In resource-limited or basic clinical microbiology labs, we can still suspect or screen for Candida auris using a combination of culture characteristics, resistance patterns, and simple tests.

Fig. Candida auris colony morphology-Source: CDC

When to Suspect C. auris?

Rapid-growing yeast in high-risk patients (ICU, cancer).
Shows resistance to fluconazole.
Doesn’t form germ tubes.
Grows at 42°C and in 10% NaCl.
Misidentified by automated systems.

Identification Methods In a Simple Setup

1. Growth on Chromogenic Media (e.g., CHROMagar Candida)

Candida auris typically grows as pale pink to white colonies, but NOT green (like C. albicans), not metallic blue (like C. tropicalis).
However, C. auris may resemble C. glabrata or C. haemulonii on chromogenic media, so this is presumptive only.

2. Salt and Temperature Tolerance

C. auris can grow in:
- 10% NaCl (Halotolerant)
- 42°C incubation (Thermotolerant)
Set up Sabouraud dextrose agar (SDA with NaCl and incubate at 42°C for 48 hours.

3. Antifungal Resistance Profile

Test antifungal susceptibility using disc diffusion or MIC strips (if available).
C. auris typically shows:
- Resistance to fluconazole (FLC)
- Variable resistance to amphotericin B and echinocandins
If a Candida isolate shows multidrug resistance, suspect C. auris.

4. Colony Morphology on SDA

Smooth, shiny, white-to-cream-colored colonies.
Grows rapidly (24–48 hrs) at 37°C.

5. Gram Stain / Microscopy

Oval yeast cells; no pseudohyphae or germ tubes.
However, this is not sufficient alone for ID.

6. Sugar Assimilation (Optional)

You may perform basic sugar assimilation tests (e.g., dextrose, galactose, maltose, lactose).
C. auris is non-hemolytic, and its sugar assimilation profile differs from C. albicans.

What We CANNOT Do in Simple Labs:

MALDI-TOF MS
PCR or sequencing
VITEK-2 without an updated database may misidentify it as C. haemulonii or C. famata

Confirmatory Identification

The isolate is sent to the reference lab for:

MALDI-TOF MS (updated database)
PCR targeting the ITS/D1-D2 region
Whole-genome sequencing (if part of the outbreak)

Summary Table for Candida auris Screening

Test	Result Suggestive of C. auris
Chromagar	Pale pink/white colonies
Germ tube	Negative
Growth at 42°C	Positive
Growth in 10% NaCl	Positive
Fluconazole resistance	Common
Germ tube	Absent
MALDI-TOF (if available)	Confirmatory

Keynotes

Emerging Multidrug-Resistant Yeast; Candida auris is a rapidly emerging fungal pathogen with resistance to multiple antifungals, including azoles, polyenes, and sometimes echinocandins.
Difficult to Identify in Routine Labs-It is often misidentified as C. haemulonii, C. famata, or C. lusitaniae by conventional systems (e.g., VITEK-2 without updated database).
Causes Invasive Infections: Common infections include candidemia, wound infections, and ventilator-associated pneumonia, especially in ICU and immunocompromised patients.
High Mortality Rates: Mortality from C. auris bloodstream infection ranges from 30% to 60%, particularly in critically ill or cancer patients.
Transmits Person-to-Person: Unlike other Candida species, C. auris spreads nosocomially (via healthcare contact, contaminated surfaces, or devices).
Grows at High Temperature and Salinity: It can grow at 42°C and in 10% NaCl, helping distinguish it from other Candida species.
No Germ Tube Formation: C. auris is germ tube negative and does not produce pseudohyphae, which helps rule out C. albicans.
Forms Biofilms on Medical Devices: Adheres to catheters, ventilators, and hospital surfaces, making eradication and infection control challenging.
Resistant to Fluconazole: >90% of isolates are resistant to fluconazole; some strains are pan-resistant to all major antifungal classes.
Requires Contact Precautions and Outbreak Control: Identification mandates notification, isolation, surface disinfection, and public health alert due to outbreak potential.

Candida auris Screening in a Simple Setup: Introduction, When to Suspect it, Identification Methods,Confirmatory Identification, and Summary Table