VITEK 2 Yeast Identification: Introduction, Name of Card, Principle,

Introduction

Table of Contents

The VITEK 2 Yeast Identification (YST) system is an automated platform designed for the rapid identification of clinically significant yeasts and yeast-like organisms.

Fig. Vitek 2 Compact System for Yeast Identification

It significantly reduces the turnaround time from several days (traditional methods) to approximately 15 to 18 hours.

Name of the Card

The card used is the VITEK 2 YST Card (Identification of Yeasts and Yeast-like Organisms).

fIG. VITEK 2 YST Card Information and Organisms Identified

Principle

The system utilizes advanced colorimetric technology. The YST card contains 64 microwells with 47 different biochemical tests, including:

Carbon source utilization (assimilation) of various carbohydrates.
Enzymatic activities (e.g., arylamidases, phosphatases, urease).
Resistance/Inhibition tests (e.g., actidione/cycloheximide).

The instrument monitors these wells every 15 minutes, measuring light attenuation to detect growth or metabolic changes. A specific algorithm then compares the resulting “biochemical profile” against a comprehensive database.

Procedure

The standardized workflow involves the following steps:

Culture: Grow the isolate on appropriate agar (e.g., Sabouraud Dextrose Agar) to obtain pure, young colonies.
Suspension: Aseptically transfer colonies into 3.0 mL of sterile saline (0.45% to 0.50% NaCl).
Turbidity Adjustment: Adjust the suspension to a McFarland standard of 1.80 to 2.20 using a DensiCHEK meter.
Loading: Place the suspension tube and YST card into a cassette.
Processing: The instrument automatically fills the card via vacuum, seals it to prevent contamination, and begins incubation at 35.5°C.

Result Interpretation

The software analyzes the metabolic data and provides one of the following outputs:

Unequivocal Identification: A single species is identified with a high percent probability (e.g., “Excellent,” “Very Good,” or “Good”).
Low Discrimination: The system cannot distinguish between 2 or 3 closely related organisms. It will provide a list of possibilities and suggest supplemental tests (e.g., morphology on cornmeal agar) to finalize the ID.
No Identification: The biochemical profile does not match any known patterns in the database.
Inconsistent Results: Usually indicated by a red flag, suggesting technical issues like a mixed culture or incorrect inoculum density.

Organisms Identified

The YST database currently includes approximately 50–60 taxa. Key identified groups include:

Candida species: C. albicans, C. glabrata, C. tropicalis, C. parapsilosis, C. krusei, C. lusitaniae, and C. dubliniensis.
Cryptococcus species: C. neoformans and C. gattii.
Other Yeasts: Saccharomyces cerevisiae, Rhodotorula spp., Trichosporon spp., and Geotrichum spp.

PDF: VITEK® 2 YST Card Information and Organisms Identified

Keynotes

Gram Stain Requirement: Always perform a Gram stain first to confirm the organism is indeed a yeast before using the YST card.
Suspension Age: The prepared suspension must be used within 30 minutes.
Limitations: Some rare or newly described species may be misidentified or require molecular methods for definitive ID.
Safety: The card is a closed system, which minimizes the risk of laboratory-acquired infections from aerosols.

VITEK 2 Yeast Identification: Introduction, Name of Card, Principle, Procedure, Result-Interpretation, Organisms Identified, and Keynotes