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Candida albicans– Habitat, Morphology, Cultural Characteristics, Life Cycle, Pathogenesis, Lab Diagnosis, Treatments, Prevention and Control
Habitat of Candida albicans
- Normal Habitat: mucosal membranes of human and other warm blooded animals.
- Also found in the gut, the vagina or also in the surface of the skin.
- Found in the digestive tract of birds also.
- Isolated from soil, animal, hospitals, in-animate objects and food.
- Worldwide distribution
Morphology of Candida albicans
- Small, oval, measuring 2-4 µm in diameter.
- Yeast form, unicellular, reproduce by budding.
- Single budding of the cells may be seen.
- Both yeast and pseudo-hyphae are gram positive.
- Encapsulated and diploid, also form true hyphae.
- Polymorphic fungus (yeast and pseudohyphal form)
- Can form biofilms
- Normal condition: Yeast
- Special condition (pH, Temperature): Pseudohyphae
- 80-90% of cell wall is carbohydrate
Cultural Characteristics of Candida albicans
- Creamy, pasty colonies, smooth after 24-48 hours at 25-37°C
- Yeast smell (odour)
- White creamy colored
- Foot-like extensions from the margin.
- Smooth creamy colonies after 24-48 hours
- Green colonies
Life Cycle of Candida albicans
- Asexual and doesn’t perform meiosis
- Ability to grow with three distinct morphologies- yeast, pseudo-hyphae and true hyphae
- Para-sexual life cycle
- Switch between different phenotypes
- Diploid Stage à form cells à homozygous à phenotypic switch from white to mating component ‘opaque’ cells à mating of opaque cells (cell fusion) à tetraploid cells à loss of chromosomes (splitting) à Diploid State
- White form: white and rounded cells forming dome-shaped colonies
- Opaque form: opaque, elongated cells forming a flatter colony.
- Opaque form is more efficient for mating than the white form
Pathogenesis of Candida albicans
- Opportunistic fungal pathogen that causes candidiasis in human
- Occurs in immunocompromised peoples such as HIV infected, transplant recipients, chemotherapy patients, etc.
- Mode of transmission:
- Mother to infant through childbirth
- Rarely through sexual contact
- People to people transmission in hospital settings
Virulence Factors of Candida albicans
- Yeast, pseudohyphae and hyphae
- Hyphae is more important for infection
- Adhesins (Als 3 Protein)
- Sets of glycosylphatidylinositol (GPH)- linked cell surface glycoproteins that allow it to the surfaces of microorganisms
- Helps with biofilm formation also
- Invacins (Als 3 Protein)
- Helps with the invasion of C. albicans into host epithelial and endothelial cells.
- Ssa1 codes for heat shock protein
- Induces host cells to engulf the fungal pathogens
- Invasion by the active penetration of C. albicans into host cells by involving hyphae.
- Biofilm Formation
- Yeast cells à adherence à surface à development of hyphae cells à in the upper part of biofilm à leads to a more resistant mature biofilm à dispersion of yeast cell.
- Bcr1, Tec1 and Efg1 function as important transcriptional factors.
- Secreted hydrolases
- 3 main classes of hydrolases: proteases, phospholipases and lipases
- Helps in active penetration into host cells
- Helps in uptake of extracellular nutrients from the environment.
- 10 proteases (Sap 1-10), 4 major classes (A, B, C and D) of phospholipases and lipases consist of 10 members (LIP 1-10).
- Metabolic Adaption
- In the process of infection, it undergoes metabolic adoption such as their glycolysis, gluconeogenesis and starvation responses.
- Example: quickly switch from its glycolysis to starvation responses with the activation of glyoxylate cycle.
- Due to this, it can infect almost any organ through the blood stream.
Stages of Infection
- Epithelial adhesion
- Nutrient acquisition
- Superficial Infection
- Epithelial penetration
- Degradation of host protein
- Deep-Seated Infection
- Tissue penetration
- Vascular invasion
- Immune evasion or escape
- Disseminated Infection
- Endothelial adhesion
- Infection of other host tissues
- Activation of coagulation and blood clotting cascades.
Types of Candidiasis
- Oral candidiasis: mucous membrane of mouth
- Denture related stomatitis: mild inflammation and redness of oral mucous membrane beneath a denture.
- Angular cheilitis: inflammation of one or both corners of the mouth
- Median rhomboid glossitis: redness and loss of lingual papillae
- Vulvovaginitis: white lesions on the epithelial surfaces of vulva, vagina and cervix
- Balanitis: infection of glans penis
- Esophageal candidiasis: infection of esophagus painful swallowing.
- Candida folliculitis: infection and inflammation of hair follicles, rash may appear as pimples.
- Candidal intertrigo: infection of skin located between intertriginous folds of adjacent skin.
- Candidal paronychia: inflammation of the nail fold.
- Perianal candidiasis: irritation of the skin at the exit of the rectum.
- Chronic mucocutaneous candidiasis: immune disorder of T cells, deficient of CMI.
- Congenital cutaneous candidiasis: skin condition in new borne babies caused by premature rupture of membranes together with a birth canal infected with C. albicans.
- Diaper candidiasis: infection of a child’s diaper area.
- Erosio interdigitalis blastomycetia: characterized by an oval shaped area of macerated white skin on the web between and extending onto the sides of the fingers.
- Candidal onychomycosis: nail infection
- Candidemia: leads of sepsis
- Disseminated candidiasis (organs)
- Gastro intestinal tract infection
- Respiratory tract infection
- Genitourinary candidiasis
- Hepatosplenic candidiasis (Chronic Disseminated Candidiasis)
Lab Diagnosis of Candida albicans
Specimens: Exudates, Tissues, Scrapings
- Microscopy (Scraping)
- Examined in wet film in 10% KOH
- Visualization of pseudohyphae and budding yeast cells of candida
- Gram staining: Gram positive (+ve)
- SDA: Creamy white, smooth colonies
- CHROMAGAR: Green colonies
- Identification of albicans
- Germ Tube Test: produce germ tube test within 2 hours when incubated in human serum at 37°C.
- Chlamydospores: produced by C. albicans on corn meal/rice agar at 25°C. They produces round thick walled chlamydospores borne terminally or laterally.
- Biochemical Tests: Glucose and maltose fermented with acid and gas production, sucrose and lactose not fermented, Pale pink coloration in Tetrazolium reduction medium
- Limited specificity
- Serum antibodies and cell mediated immunity are demonstrable in most people because of life long exposure to C. albicans.
- C. albicans antigen is a delayed hypersensitivity skin test, which is used as an indicator of functions of the CMI.
- ELISA and RIA: detection of circulating Candidial antigen either cell wall mannan or cytoplasmic constituents.
- 1,3-beta-D-glucan assay
- Beta-D-glucan is a component of the cell wall of fungi.
- Detected by its ability to activate factor G of the horse-shoe crab coagulation cascade.
- Highly specific and sensitive test.
- DNA probe and PCR
Treatments of Candida albicans
- Oral candidiasis: Nystatin, miconazole, amphotericin B.
- Cutaneous candidiasis: Clotrimazole, econazole, ciclopirox, miconazole, ketoconazole, nystatin.
- Systemic and oral azoles: Fluconazole, itraconazole or posaconazole.
- Vulvovaginitis: single dose of oral fluconazole, topical antifungals (butoconazole, clotrimazole, miconazole, nystatin, ticonazole, terconazole).
- Blood infections: intravenous fluconazole or an echinocandin (caspofungin)
- Candidemia: Fluconazole and Anidulafungin
Prevention and Control of Candida albicans
- Keep healthy life style
- Good hygiene, proper nutrition, careful antibiotic use.
- Add probiotics, reduce sugar intake
- Wear cotton underwear and loose pants
- Change immediately wet clothes