Therapeutics ID Santanello Flashcard

Fungal Morphology

Multicellular Branching Filamentous (hyphae) Forms

  • Mass of hyphae is a mycelium
  • Asexual reproduction results in spores formed from hyphae
  • Sexual spores as well (less common)

 

Unicellular Yeast

  • Reproduce by budding or division

Characteristics of Fungal Cell Wall/Cell Membrane

3 layers of polysaccharides

Glycoproteins

Beta-Glucans

Alpha-Glucans

 

Chitin and Mannans are significant components of fungal cell wall

 

Main Sterol Components of Cell Membrane

Ergosterol

Zymosterol

Route of Fungal Infections

  • Inhalation
  • Ingestion
  • Injection

What can prevent fungal colonization?

Low pH

Fatty acids

Turnover of skin

IgA, IgG at mucosal surfaces

Our own flora

Fungi cause disease through 3 main mechanisms:

  1. Hypersensitivity to fungal antigens
  2. Production of mycotoxins (exotoxins)
  3. Mycoses – growth of a fungus on or in the body

Types of Mycoses

  1. Superficial
  2. Subcutaneous
  3. Systemic (primary pathogenic and opportunistic fungi)

Superficial Mycoses

  • Body surface (skin, hair, nails)

Ex: dermatophytosis (ringworm) affects outermost keratinized tissues of the hair, nails, and stratum corneum of the skin

Subcutaneous Mycoses

  • Confined to the dermis, subcutaneous tissue, or adjacent structures

Ex: Rare and confined to tropical regions of the world; usually result from inoculation of saprophytic fungi from soil into subcutaneous tissue (via thorn, insect bite, fish spine)

Systemic Mycoses

  • Internal organs, systems
  • May result from inhalation of air-borne spores, ingestion, or IV lines

Primary Pathogenic Fungi

  • Infections occurs in previously healthy persons and arises through a respiratory route
  • Ex: Histoplasmosis

 

Systemic Opportunistic Fungi

  • Cause diseases in immune compromised hosts
  • Endogenous (Candida albicans)
  • Exogenous (?)

Characteristics of Dermatophytes

  • Infection of skin, hair, nails, and outer layers of epidermis
  • Causes dermatomycoses
  • Secrete keratinase, an enzyme that degrades keratin

Pathogens that cause Dermatomycoses

Trichophyton

Microsporium

Epidermophyton (Tinea capitis, pedis, cruris, corporis)

Dimorphic: Definition

  • Many pathogenic species are dimorphic
  • Capable of changing from multicellular mold form in nature to a budding single celled form when causing an infection
  • Switches to dimorphic based on environmental, temperature, and nutritional changes

Ex: Histoplasma capsulatum

Histoplasmosis

  • Histoplasma capsulatum
  • Route of infection: inhalation
  • Upon inhalation, small budding forms phagocytosed; infection of macrophages and histiocytes
  • Transient spread leads to flu-like symptoms
  • Hepatosplenomegaly in immunocompromised patients
  • Bat, bird feces provides nutrients for the fungus

 

 

Coccidioidomycosis

  • Coccidioides immitis
  • Spores found in dry soils of the Southwestern US, Central America, South America
  • Highly infective in dusts in endemic areas
  • Like Histoplasmosis, may be asymptomatic; may present as flu-like illness, similar to Tuberculosis
  • Hyphal growth in lung

Aspergillus

  • Aspergillus fumigatus, A. niger, A. flavus
  • Dangerous in immunocompromised patients
  • Aspergillus spores are nearly everywhere
  • Causes severe allergies
  • Aspergillosis of the lung (aspergilloma) may be contained but systemic aspergillosis has a high mortality

Alfatoxin B1 is produced by:

Aspergillus flavus

  • It is an aromatic amine derivative
  • From peanuts, grains
  • Mutagenic effects on the liver (forms liver tumors)

Cryptococcosis

Cryptococcus neoformans

  • Encapsulated yeast that is inhaled
  • Leads to meningoencephalitis
  • May also involve skin, UT, eyes, lungs, bones, joints, myocardium, prostate gland

What are the two forms of Cryptococcus neoformans?

1.  Weakly Encapsulated

  • in high glucose or high salts, conditions that may be found in nature, C. neoformans becomes weakly encapsulated
  • the small size is necessary for the organism to get into the alveolar spaces in the lung

2.  Thick Polysaccharide (Rehydrated) Capsule

  • once in the lungs, the organism can become rehydrated and acquire a thick polysaccharide capsule

Pneumocystis

Pneumocystis carinii (Pneumocystis jiroveci)

  • Opportunistic infection of elderly, premature babies, immune compromised
  • Lung tissue infected –> filling of alveoli w/ fluids

 

Yeast

  • Nonfilamentous, unicellular; typically oval or spherical
  • Like molds, found almost everywhere
  • Candida albicans causes Candidiasis, thrush
  • Skin lesions: vulvovaginitis, otomycosis, onychomycosis
  • Also, C. glabrata, C. lusitaniae

Claviceps purpurea

  • LSD synthesized from this fungus
  • Intensifies sense perceptions
  • MOA: Blocking serotonin function in the brain

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