Candida albicans- Habitat, Morphology, Cultural Characteristics, Life Cycle, Pathogenesis, Lab Diagnosis, Treatments, Prevention and Control

Candida albicans- Habitat, Morphology, Cultural Characteristics, Life Cycle, Pathogenesis, Lab Diagnosis, Treatments, Prevention and Control

Candida albicans– Habitat, Morphology, Cultural Characteristics, Life Cycle, Pathogenesis, Lab Diagnosis, Treatments, Prevention and Control

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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

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

SDA

Candida albicans on SDA
Candida albicans on SDA
  • Creamy, pasty colonies, smooth after 24-48 hours at 25-37°C
  • Yeast smell (odour)

Blood Agar

Candida albicans on Blood Agar
Candida albicans on Blood Agar
  • White creamy colored
  • Foot-like extensions from the margin.

PDA

  • Smooth creamy colonies after 24-48 hours

CHROMAGAR

Candida albicans on Chromagar
Candida albicans on Chromagar
  • Green colonies

Life Cycle of Candida albicans

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

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

  1. Polymorphism
  • Yeast, pseudohyphae and hyphae
  • Hyphae is more important for infection
  1. 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
  1. 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.
  1. 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.
  1. 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).
  1. 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

  1. Colonization
  • Epithelial adhesion
  • Nutrient acquisition
  1. Superficial Infection
  • Epithelial penetration
  • Degradation of host protein
  1. Deep-Seated Infection
  • Tissue penetration
  • Vascular invasion
  • Immune evasion or escape
  1. Disseminated Infection
  • Endothelial adhesion
  • Infection of other host tissues
  • Activation of coagulation and blood clotting cascades.

Types of Candidiasis

Mucosal 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.

Cutaneous Candidiasis

  • 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

Systemic Candidiasis

  • Candidemia: leads of sepsis
  • Disseminated candidiasis (organs)
  • Endocarditis
  • Gastro intestinal tract infection
  • Respiratory tract infection
  • Genitourinary candidiasis
  • Hepatosplenic candidiasis (Chronic Disseminated Candidiasis)

Lab Diagnosis of Candida albicans

Specimens: Exudates, Tissues, Scrapings

  1. Microscopy (Scraping)
  • Examined in wet film in 10% KOH
  • Visualization of pseudohyphae and budding yeast cells of candida
  • Gram staining: Gram positive (+ve)
  1. Culture
  • SDA: Creamy white, smooth colonies
  • CHROMAGAR: Green colonies
  1. 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
  1. Serology
  • 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. 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.
  1. DNA probe and PCR

Treatments of Candida albicans

Treatments of Candidiasis

  1. Oral candidiasis: Nystatin, miconazole, amphotericin B.
  2. Cutaneous candidiasis: Clotrimazole, econazole, ciclopirox, miconazole, ketoconazole, nystatin.
  3. Systemic and oral azoles: Fluconazole, itraconazole or posaconazole.
  4. Vulvovaginitis: single dose of oral fluconazole, topical antifungals (butoconazole, clotrimazole, miconazole, nystatin, ticonazole, terconazole).
  5. Blood infections: intravenous fluconazole or an echinocandin (caspofungin)
  6. 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

Candida albicans– Habitat, Morphology, Cultural Characteristics, Life Cycle, Pathogenesis, Lab Diagnosis, Treatments, Prevention and Control

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