Chapter 22- Pathogenic Fungi Flashcards
What are some general characteristics about fungi?
Chemoheterotrophic
Cell walls contain chitin
Do not perform photosynthesis - lack chlorophyll
Genetic sequencing shows that fungi are more related to animals
What are some common terms associated with fungal morphology?
Thallus- vegetative (non-reproductive) body
Molds- thallus composed of long branched tubular filaments known as hyphae, hyphae may be spetate or aseptate
Mycelium- hyphae intertwined to form tangled mass of molds
Yeasts- small, globular, single cell
If produce both types of thalli - dimoprhic
How do fungi reproduce?
Budding and asexual spore formation - yeasts bud in a similar manner to prokaryotic budding
Pseudohypha- series of buds that remain attached to one another and to the parent cell (Candida albicans)
Filmentous fungi produce lightweight spores that disperse over large surfaces
What are the 3 clinical manifestations of fungal diseases?
Fungal infection- commonly mycoses, acquired by inhalation, trauma, or ingestion, caused by true pathogens or opportunists
Toxicoses (poisonings)- ingestion of mycotoxins e.g. aflatoxin, mycetismus- ingestion of poisonous mushrooms
Allergies- hypersensitivity reaction, result from inhalation of spores
What are some characteristics of the systemic mycoses caused by pathogenic fungi?
Infection spreads throughout the body
Caused by 1 of 4 pathogenic fungi of division Ascomycota: Blastomyces, Coccidioides, Histoplasma, and Paracoccidiodes
Acquired by inhalation - begins as generalized pulmonary infections, disseminates via blood
All are dimorphic
How are mycoses diagnosed and treated?
Diagnosis- patient’s history, morphological analysis of fungal cells
Sabouraud dextrose agar- used to culture fungi
Staining techniques- KOH preparation, Gomorimethenamine silver stain, Direct immunofluorescence stain
Treatment- Amphotericin B, Azoles, 5-fluorocytosine, and griseofulvin
What is the disease Histoplasmosis? What is caused by and where is it most common?
Histoplasma capsulatum is causative agent
Most common fungal pathogen affecting humans
Mostly in eastern U.S. (Ohio River Valley), Africa, and Asia
Fungi found in soils high nitrogen levels from bird and bat droppings
Intracellular parasite - alveolar macrophages
What are the four diseases caused by histoplasma capsulatum?
Chronic pulmonary histoplasmosis - severe coughing, blood tinged sputum, weight loss, often mistaken for TB
Chronic cutaneous histoplasmosis- ulcerative skin lesions
Systemic histoplasmosis- enlargement of spleen and liver
Ocular histoplasmosis
How is a histoplasmosis infection diagnosed and treated?
Diagnosis based on distinctive budding yeast in KOH- or GMS- prepared samples and dimorphism cultures
Characteristic spiny spores
Infections in healthy individuals resolved on own
Amphotericin B
What are some characteristics of the disease blastomycosis?
Causative agent: Blastomyces dermatitidis
Endemic in Southeastern U.S. north to Canada
Found in cool, damp soil
Pulmonary blastomycosis most common
Other conditions: cutaneous blastomycosis, osteoarticular blastomycosis, meningitis
What are some characteristics of Coccidiomycosis?
Causative agent- coccidiodes immitis
Almost exclusively found in southwestern US and Northern Mexico
Fungi found in desert soil, rodent burrows, archaeological remains, mines, and transmission is through contaminated dust
If inhaled, arthoconidia germinate into spherules in lungs
Diagnosis- coccidioin skin test
Treatment- Amphotericin B, maintenance with azoles
What are some characteristics of Paracoccidioidomycosis?
Causative agent- Paracoccidioides brasiliensis
Found in the cool, damp soil of Southern Mexico and regions of South America
Found in farm works in endemic areas
Fungus spreads and produces chronic inflammatory disease of mucous membranes, painful ulcerated lesions of gums, tongue, lips, and palate
Diagnosis- “steering wheel” formation of buds
Treatment- Amphotericin B or ketoconazole
What are some characteristics of the types of systemic mycoses casued by opportunistic fungi?
Don’t typically affect healthy humans - limited to people with poor immuntiy, more important as number of AIDS patients increases
Difficult to identify because symptoms are often atypical
5 genera- pneumocystis, candida, aspergillus, cryptococcus, and mucor
What are some characteristics of Pheumocystis Pneumonia?
Causative agent- pneumocystis jiroveci, obligate parasite
Majority exposed to P.jiroveci by age 5
Infection in immunocompetent is usually asymptomatic
Common opportunistic fungal infection in AIDS patients- diagnostic for AIDS
Enters lungs and colonizes tissue rapidly and extensively
Inflammation, fever, difficult breathing, non=productive cough
Can result in death if left untreated
Treatment- sulfanilamides and trimethoprim
What are some characteristics of Candidiasis?
Causative agent- Candida albicans
Common members of microbiota of skin and mucous membranes
One of few fungi transmitted between individuals- to baby during childbirth or men during sexual contact
Wide range of diseases- Oropharyngeal candidiasis or thrush, diaper rash, nail infection, ocular candidiasis
