L7 Opportunistic Mycoses

• Infections that occur almost exclusively in debilitated px. whose normal defense mechanisms are impaired
• Increased incidence paralleled the emergence of AIDS, more aggressive cancer and post-transplantation chemotherapy, & the use of antibiotics, cytotoxins, corticosteroids, immunosuppressives, & other macro disruptive procedures resulted in lowered resistance of host
• Opportunistic invasive mycoses


  • Endogenous yeasts, normal mammalian microbiota
  • Exogenous fungi, in soil, water, and air
• Candida species


  Found in the mouth, skin, gut, GUT
• Candida albicans


  • Initially was a true yeast
  • Now classified as dimorphic = can produce a true hyphae
  • Can produce longer hyphae septated hyphae after germ tubes even @37°C
• Candida albicans produces true hyphae
• Candida albicans is positive to germ tube
• Candida species grow as oval, budding yeast cells and pseudohyphae (where chains of elongated cells fail to detach) with septations between cells
• Within 24h, 37°C or RT: Candida species grow as soft, creamy colonies with a yeasty odor
• Every year, reports of novel infections caused by those previously thought to be nonpathogenic
• CANDIDIASIS


  Members of the normal flora of skin, mucous membranes, and gastrointestinal tract
• Most common Candida agents

  • C. albicans (most common pathogen & only dimorphic spp.)
  • C. parapsilosis
  • C. glabrata
  • C. tropicalis
  • C. dubliniensis
• C. albicans


  Germ Tube (+) & chlamydospore (+)
• GERM TUBE TEST


  1. Use 0.5 mL of rabbit, horse, & human serum

  2. Add yeast colonies

  3. Incubate for 2% to 3 hours at 37C

  4. POSITIVE: Appendage half the width, 3x-4x length of yeast, no point of constriction at origin
• CORNMEAL TWEEN 80 AGAR


  Showcases the chlamydospores
• Azole resistant Candida species

  • C. glabrata
  • C. krusei
  • C. lusitaniae
  • C. auris (most alarming, not part of microbiota)
• Candida species can cause both cutaneous and systemic infections
• Clinical manifestations of Candida infections have different mechanisms of pathogenesis
• Candida morphology & identification

  • Grow as oval, budding yeast cells (3-6 pm), form pseudohyphae (when buds continue to grow but fail to detach)
  • Chains of elongated cells, pinched or constricted at septations between cells
  • Submerged below agar surface
  • Soft, cream-colored colonies with a yeasty odor within 24h, 37°C or RT
• C. albicans

  Dimorphic (unlike other Candida spp.), produces true hyphae or germ tubes, positive to germ tube test
• Other Candida spp.


  Only yeasts, do not produce pseudohyphae
• Nutritionally Deficient Media


  Produce large, spherical yeast cells
• Confirmatory test & speciation

  Sugar fermentation & Assimilation tests
• Candida spp. that only have yeast cells, no pseudohyphae

  • C. albicans
  • C. tropicalis
  • C. parapsilosis
  • C. guilliermondii
  • C. kefyr
  • C. krusei
  • C. lusitaniae
• Antigenic structure of C. albicans

  Two serotypes: A (includes C. tropicalis) and B
• Cell wall components of Candida

  • Mannans, glucans, other polysaccharides, glycoproteins, enzymes
• Cell wall components

  Released during infection, facilitate attachment & invasion of host cells, elicit innate defenses & Th1, Th17, Th2 immune responses
• Prolonged use of antibiotics reduces good bacteria, increasing Candida population which damages the epithelium through local invasion by yeasts/pseudohyphae
• Acute Phase of Candidiasis

  Pyogenic abscesses
• Chronic Phase of Candidiasis

  Granulomatous lesions
• Administration of broad-spectrum antibiotics promotes large increases in the endogenous population of Candida in the GIT, oral, & vaginal mucosa
• 2 types of Candidiasis

  • Systemic
  • Nosocomial
• Systemic Candidiasis


  Candida spp. enters the bloodstream, and innate phagocytic host defenses are inadequate to contain the growth and dissemination of the yeasts
• Nosocomial Candidiasis


  From contaminated indwelling IV catheters
• Candida biofilms


  • Form with extracellular matrix, resist penetration by host immune responses and antifungal drugs
• Risk factors for Cutaneous and Mucosal Candidiasis

  • AIDS, pregnancy, diabetes, young or old age, birth control pills, trauma (burns, maceration of the skin)
• Thrush


  Occurs on the tongue, lips, gums, or palate, patchy confluent, whitish pseudomembranous lesions, form intractable biofilm
• Vulvovaginitis/Monilial vaginitis/Vaginal yeast infection

  Yeast invasion of the vaginal mucosa, irritation, pruritus, vaginal "curdy" discharge (lumps of cottage cheese), pale to red labia, burning on urination
• Monilia


  Former genus of Candida
• Intertriginous Infection


  Occurs in moist, warm parts of the body (axillae, groin, intergluteal or inframammary folds), common in obese & the diabetic