Lecture 32

• The most common mycoses

  • Candidiasis
  • Aspergillosis
• The most common agents of Candidiasis

  • C. albicans
  • C. parapsilosis
  • C. glabrata
  • C. tropicalis
  • C. guilliermondii
  • C. dubliniensis
• Candida colonies on Sabouraud dextrose agar

  • Yeast-like colonies
  • Round-ovoid shape (2-4 mm diameter)
  • Cream color
  • Soft, silky
  • Yeasty odor

  
• Candida cells under microscopy

  • Single cell (unicellular)
  • Yeast cells and buds
  • Round, oval, to cylindrical, size 2-7 x 3-8.5 μm
  • Form true hyphae or germ tubes

  
• Tests to differentiate C. albicans from others

  1. Incubation in serum 90 minutes at 37°C, forms true hyphae or germ tube

  2. Nutrient deficient media: produces large spherical chlamydospores

  
• Candida albicans serotypes


  A and B
• What Candida albicans can release during infection

  • Mannan, glucan, other polysaccharides, glycoproteins, enzymes

  
• Pathogenesis of Candidiasis


  1. Adhesion to epithelial cells

  2. Produce protease enzymes, hyaluronidase, chondroitin sulfatase and phospholipase

  3. Phospholipases hydrolyze phospholipids of epithelial cell membranes

  4. Proteases and other enzymes are keratolytic, facilitates penetration into the epidermis
• Virulence factors of Candida spp.

  • Change from yeast cells to mycelials (pseudohyphae)
  • Ability to grow at a certain temperature
  • Ability to adhere to epithelial cells
  • Ability to grow in the form of filaments
  • Activity of the enzymes produced

  
• Cell wall of Candida


  • Contains mannan, can activate complement and stimulate the formation of antibodies
• Laboratory diagnosis of Candidiasis

  Specimen includes: swab and scraping of superficial lesions, blood, spinal fluid, tissue biopsies, urine, fluid exudate
• Microscopic examination for Candidiasis

  • Cheap, simple, fast, minimal equipment
  • Sensitivity 50-80%, using KOH, LPCB staining
  • Gram stain, Observe yeast cells, pseudohyphae

  
• Culture for Candidiasis


  1. All samples taken can be cultured on SDA medium at room temperature or at 37°C

  2. Positive blood culture is an indication of systemic candidiasis

  
• Germ tube formation test

  Candida spp colonies in serum incubated at 37°C for 90 minutes, distinguishes Candida albicans from other Candida

  
• Aspergillosis


  A disease caused by Aspergillus species
• Some Aspergillus species


  • Aspergillus fumigatus
  • Aspergillus flavus
  • Aspergillus niger
  • Aspergillus terreus
  • Aspergillus lentulus
• Aspergillus morphology


  • Can grow rapidly, producing high aerial hyphae
  • Has a characteristic conidial structure with long conidiophores and terminal vesicles
  • Phialides produce basipetal conidial chains
• Identification of Aspergillus species

  Based on morphology of conidial structure, size, shape, texture, and color of the conidia
• Pathogenesis of Aspergillosis in immunocompetent individuals

  Conidia inhaled, reach alveolar lungs, alveolar macrophages phagocytose and destroy them
• Pathogenesis of Aspergillosis in immunocompromised patients


  Macrophages unable to phagocytize, conidia enlarge, germinate, hyphae invade existing cavities or blood vessels
• Forms of Allergic Aspergillosis

  • Asthmatic reaction due to exposure to Aspergillus conidia surface antigen
  • Allergic bronchopulmonary aspergillosis
  • Extrinsic allergic alveolitis from massive exposure to conidia
• Aspergilloma


  Occurs when conidia are inhaled, enter cavities, germinate, producing lots of hyphae in abnormal lung spaces
• Patients at risk of Aspergilloma

  • Those with tuberculosis, sarcoidosis, and emphysema
• Invasive aspergillosis


  Develops as an acute pneumonia process with or without dissemination
• Patients at risk of invasive aspergillosis


  • Lymphocytic leukemia and lymphoma patients
  • Stem cell transplant recipients
  • Patients taking corticosteroids
  • AIDS patients with CD4 cell counts less than 50 CD4 cells/µL
• Laboratory diagnosis of Aspergillosis

  1. Specimen: sputum, lung biopsy, blood

  2. Microscopic examination: hyphae are hyaline, septate, and uniform in width (about 4 µm)

  3. Culture: Aspergillus grows in a few days at room temperature, species identified by conidial structure morphology

  
• Endemic fungal infections: Histoplasmosis, Blastomycosis, Coccidioidomycosis, Paracoccidiomycosis
• Opportunistic fungal infections: Candidiasis, Aspergillosis
• Histoplasmosis


  Infection caused by the fungus Histoplasma capsulatum
• How people get histoplasmosis

  • Inhalation of microscopic fungal spores from the air, although most people who inhale the spores don't get sick
• Histoplasmosis in immunocompromised patients

  • Can be very serious with mortality rate ranges from 20 to 40%
• Regions where Histoplasma is most common

  • North America and Central America
  • Parts of Central and South America, Africa, Asia, and Australia
• Where Histoplasma thrives


  • Soil or other environmental material containing bird or bat droppings
• Risk factors for histoplasmosis

  • Live in area with Histoplasma
  • Doing activities that disturb soil that contains bird or bat droppings
  • Immunocompromised patients (HIV/AIDS, organ transplant, taking corticosteroids/immunosuppressant, infants, elderly)
• No human-to-human transmission of histoplasmosis (except in extremely rare case through organ transplant)
• Pets (particularly cats) can get histoplasmosis but not contagious between animals & people
• Histoplasma capsulatum morphology


  • Mycelia have microconidial and macroconidial forms, microconidia are small enough to reach the terminal bronchioles and alveoli
  • Shortly after infecting the host, mycelia transform into the yeasts that are found inside macrophages and other phagocytes
  • The yeast forms are characteristically small (2–5 μm), with occasional narrow budding

  
• Pathogenesis of histoplasmosis in immunocompetent individuals

  1. Inhalation of microconidia reach the alveolar spaces, rapidly recognized and engulfed by alveolar macrophages, transform into yeasts

  2. Yeasts multiply inside resting macrophages and use the phagosomes as a vehicle for translocation to local draining lymph nodes and spread hematogenously throughout the RES

  3. Adequate cellular immunity develops ∼2 weeks after infection, IFN-γ, IL-12 and TNF-α play an essential role

  4. Macrophages, lymphocytes, and epithelial cells eventually organize and form granulomas that contain the organisms
• Pathogenesis of histoplasmosis in immunocompromised individuals

  Impaired cellular immunity, the infection is not properly contained and can disseminate throughout the RES
• Unlike latent tuberculosis, inactive histoplasmosis does not reactivate