Candida albicans is an endogenous organism, found in 40 to 80% of normal human beings as commensal in gastrointestinal tract, oropharynx . It is a commonest cause of candidiasis (moniliasis). Candida albicans is gram positive yeast with a single bud (some of the multiple choice questions test your knowledge regarding this fact; e.g., MCQs like, ‘all of the following organisms are dimorphic fungi except’; or ‘which of the following fungal pathogen is Gram positive in nature’). Other most common isolate of Candida species are Candida tropicalis, Candida parapsilosis, and Candida glabrata.
In direct stained smear (of the pathogenic sample), the yeasts can often be seen attached to pseudohyphae. Both the yeasts and pseudohyphae are Gram positive.
Most Candida infections are opportunistic, occurring when a patient has some alteration in cellular immunity, normal flora or normal physiology. Infection may be caused by endogenous yeasts or many be nosocomial. Candidiasis is the most common fungal infection in HIV infected individuals.
- The more debilitated the host, the more invasive the disease.
- Associated with prolonged broad-specturm antibiotic or steroid therapy
- Invasive procedures e.g. surgery / indwelling catheters predispose to Candida
Fibronectin receptor on Candida albicans facilitates its adherence to the (fibronectin, a component of the host extracellular matrix) epithelium of the gastrointestinal or urinary tract. Hydrophobic molecules on the surface of Candida also helps in adhesion. Aspartyl proteases found in C. albicans has shown increased ability to cause disease in animal models. Phenotypic switching and presence of phospholipase also play a role in pathogenesis.
C.albicans is responsible for several different types of infections in healthy and immunocompromised patients. Main diseases includes;
- Oropharyngeal candidiasis (oral thrush): Common in those with HIV/AIDS.
- Vulvovaginal candidiasis (vaginal thrush): Common infection during pregnancy
- Candidemia/disseminated infections
Other diseases caused by Candida are paronychia, onychomycosis, endocarditis, eye infection, intertriginous candidiasis etc. Disseminated infection of Candida and meningitis is seen mostly in immunocompromised and/or seriously ill patients.
Specimen depends on disease presentation. Common submitted sample includes; urine (in case of UTI), vaginal discharge (suspected cases of vaginal thrush) or CSF (when meningitis is suspected), sputum (when pneumonia is suspected) or other exudates from mucosal surface.
Microscopy and Staining
Candida yeast cells can be detected in unstained wet preparations or Gram stained preparations of sample. In Gram stained smears, Candida appears as gram positive budding yeast cells (blastoconidia) and/or pseudohyphae showing regular points of constriction.
Candida albicans grows well on Sabouraud dextrose agar and most routinely used bacteriological media. Cream colored pasty colonies usually appear after 24-48 hours incubation at 25-37°C. The colonies have a distinctive yeast smell and the budding cells can be easily seen by direct microscopy in stained or unstained preparations.
In Blood Agar, Candida albicans gives white, creamy colored colonies which can be mistaken for Staphylococcus spp. Whenever you are analyzing the culture report of ‘high vaginal swab’, take extra care as the colony you are observing can be of Candida albicans instead of Staphylococcus aureus or vice versa (quick solution for this is to perform wet mount or gram staining and observing under microscope).
Further tests from culture isolate:
Candida albicans can be identified presumptively by a simple germ tube test.
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