Candida auris is an emerging fungal pathogen first identified in Japan in 2009. It is a significant public health concern due to its rapid global spread and identification challenges in clinical settings. While understanding its physical characteristics is helpful, visual assessment alone is often insufficient for diagnosis. This article explores how C. auris appears under a microscope and on culture plates, and explains why visual identification is difficult.
Its Appearance Under a Microscope
Under microscopic examination, Candida auris appears as a single-celled fungus, or yeast. Its cells are typically oval or ellipsoid in shape. It reproduces through budding. C. auris can exist as individual cells or form aggregates. While it rarely forms pseudohyphae under standard conditions, it might exhibit elongated or pseudohyphal-like forms, contributing to its diverse cellular morphologies.
How It Looks on Culture Plates
When grown on standard laboratory media, C. auris typically forms smooth, white, or cream-colored colonies. Its appearance can vary significantly depending on the specific culture medium. On commercial chromogenic Candida agar, colonies may appear pink, beige, pale rose, or red. Some specialized media produce a distinctive blue halo or a uniform teal to teal-green coloration, which can aid in presumptive identification. However, these visual characteristics are not always unique to C. auris, as its colony morphology can resemble other common Candida species, making visual differentiation challenging.
Why Visual Identification Is Difficult
Despite its described features, visual identification of C. auris is unreliable in clinical laboratory settings. Candida auris shares significant morphological and biochemical similarities with other common Candida species, leading to frequent misidentification when traditional methods are used. It is commonly misidentified as Candida haemulonii, but can also be mistaken for other Candida species and even non-Candida yeasts.
These misidentifications occur because many conventional biochemical identification systems lack C. auris in their databases or have not updated their software to accurately recognize its unique profile. Relying solely on visual cues or older identification methods can result in delayed or incorrect diagnoses. Therefore, accurate identification often necessitates advanced laboratory techniques, such as Matrix-Assisted Laser Desorption/Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS) with updated databases or molecular methods like Polymerase Chain Reaction (PCR).
The Importance of Correct Identification
Accurate and timely identification of Candida auris is important for effective patient care and public health. C. auris is frequently multidrug-resistant, meaning it can withstand common antifungal treatments. Misidentification or delayed recognition can lead to ineffective therapies and poorer patient outcomes.
C. auris has an ability to spread rapidly within healthcare facilities. Correct identification allows for prompt implementation of appropriate infection control measures, such as enhanced cleaning protocols and patient isolation, which are important to prevent further transmission. Early and precise diagnosis is an important step in controlling outbreaks and limiting the spread of this pathogen in vulnerable healthcare environments.