Chapter 22 - Pathogenic Fungi Flashcards
Name and describe some of the general characteristics about fungi?
- Chemoheterotrophic
- Have cell walls typically composed of chitin
- Do not perform photosynthesis: Lack chlorophyll
- Even though fungi possess cell walls, genetic sequencing has shown that they are related to animals
What is a thallus?
The vegetative (nonreproductive) body of fungus
What is the fungal morphology?
- Thallus
- Molds
- Hyphae
- Septate or aseptate
- yeasts
- dimorphic
- mycelium
What are hyphae?
The thalli of molds are large and composed of long, branched tubular filaments
What are the different characteristics of hyphae?
Hyphae can be septate or aseptate
Describe the thalli of yeasts?
The thalli of yeasts are typically small, globular, and composed of a single cell
What is dimorphic?
Some fungi can produce both types of thalli and are said to be dimorphic
What is a mycelium?
The thallus of a mold is composed of hyphae intertwined to form a tangled mass
How do fungi repoduce?
- Budding and asexual spore formation
- Yeasts bud in manner similar to prokaryotic budding
- Pseudohypha: Series of buds that remain attached to one another and to parent cell e.g. Candida albicans
- Filamentous fungi produce lightweight spores that disperse over large distances
What are the three categories of clinical manifestations of Fungal diseases?
- Fungal infections: Most common mycoses, typically aquired via inhalation, trauma, or ingestion and caused by the presence of true pathogens or oppurtunists
- Toxicoses (poisonings): Aquired through ingestion of mycotoxins, e.g. aflatoxin, and **mycetismus ** occurs when poisonous muchrooms are eaten
- Allergies (hypersensitivity reactions): Most often result from the inhalation of fungal spores
What are the charactgeristics of Systempic Mycoses caused by pathogenic fungi?
- Infections spread throughout the body
- Caused by one of four pathogenic fungi of the division Ascomycota
- Blastomyces, Coccidioides, Histoplasma, and Paracoccidioides
- Acquired through inhalation
- Begins as generalized pulmonary infection
- Disseminates via the blood to the rest of the body
- All are dimorphic
- Individuals working with these fungi must take precautions to avoid exposure to spores
How is mycoses diagnosed?
- Patient’s history is critical for diagnosis of most mycoses
- Definitive diagnosis requires morphological analysis of the fungus
- Sabouraud dextrose agar used to culture fungi
- Various techniques used to detect fungal cells in patient specimens
e.g. KOH preparations, Gomori methenamine silver stain, Direct immunofluorescence stain
What is the treatment of Mycoses?
- Amphotericin B is gold standard of antifungals
- Azoles , 5-fluorocytosine, & griseofulvin
What is Histoplasmosis?
- Histoplasma capsulatum is the causative agent
- Most common fungal pathogen affecting humans
- Mostly in the eastern United States (Ohio river valley) but also in Africa and Asia
- Fungi found in moist soils containing high nitrogen levels
- (bird and bat droppings in soil)
- Most common infection route is inhalation of spores into the lungs
- H. capsulatum is intracellular parasite and is phagocytosed by alveolar macrophages
- Dispersed beyond the lungs via the blood and lymph
What are the diseases caused by Histoplamosis?
- Chronic pulmonary histoplasmosis: Severe coughing and blood-tinged sputum, weight loss, often mistaken for TB
- Chronic cutaneous histoplasmosis: ulcerative skin lesions
- Systemic histoplasmosis: Enlargement of spleen and liver, fatal
- Ocular histoplasmosis: Type I hypersensitity reaction in the eye
What is Coccidioidomycosis?
(Discuss characteristics, diagnosis and treatment)
- Coccidioides immitis is the causative agent
- Almost exclusively in the southwestern United States & Northern Mexico (California, Nevada, Arizona, New Mexico, Texas)
- Fungi in desert soil, rodent burrows, archaeological remains, mines, contaminated dust is a major source of transmission
- If inhaled, arthroconidia germinate into spherules in the lung
- Coccidioidomycoses most often result in pulmonary conditions
- Dissemination to other sites like CNS occurs mostly in immunocompromised individuals
- Diagnosis by coccidiodin skin test
- Treatment – Amphotericin B, maintenance with azoles
What is Paracoccidioidomycosis?
- Paracoccidioides brasiliensis is the causative agent
- Found in cool damp soil of southern Mexico and regions of South America
- Disease found most in farm workers in endemic areas
- Infection begins as a pulmonary condition
- The fungus almost always spreads
- Produces chronic inflammatory disease of mucous membranes
- Painful ulcerated lesions of gums, tongue, lips, and palate
- Diagnosis: Staining reveals yeast cells with multiple buds in a “steering wheel” formation
- Treatment is with amphotericin B or ketoconazole
What is Pneumocystis Pneumonia?
Pneumocystis jiroveci is causative agent
Obligate parasite
Majority of individuals exposed to P. jiroveci by age 5
Infection in immunocompetent is usually asymptomatic
Common opportunistic fungal infection of AIDS patients
Presence of the disease is almost diagnostic for AIDS
Once fungus enters the lungs of AIDS patient, it multiplies rapidly, extensively colonizing the lungs.
Inflammation, fever, difficulty in breathing and non productive cough are characteristic
Can result in death if left untreated
Treatment- trimethoprim and sulfanilamide
What is Candidiasis?
Includes various opportunistic infections and diseases
Candida albicans is the most common causative agent
Common members of microbiota of skin and mucous membranes
Candida is one of the few fungi transmitted between individuals
Can be passed on to babies during childbirth or to men during sexual contact
Can produce a wide range of diseases:
Oropharyngeal candidiasis or thrush
Diaper rash
Nail infection (onchomycosis)
Ocular candidiasis
What is Crytococcosis?
- Cryptococcus neoformans is the main causative agent
- Results from inhalation of spores or dried yeast in bird droppings
- Predilection for the central nervous system
- Cryptococcal meningitis
- Most common clinical form of cryptococcal infection
- Follows dissemination of the fungus to the CNS
- Other clinical manifestations- pulmonary, cutaneous cryptococcosis
What are some characteristics of cutaneous and subcutaneous mycoses?
- Pityriasis: Fungal infection of the skin causing disruption of melanin production to produce discolored patches
- Chromoblastomycosis and phaeohyphomycosis: Similar diseases resulting from dark pigmented fungi. Acquired by traumatic introduction of fungi into the skin
- Sporotrichosis (rose-gardener’s disease): Acquired from inoculation of soil fungi by thorn pricks
