Mycology Flashcards
What are the fungi types?
1) Yeasts: grow as single cells
2) Molds: grow as long hyphae and form a mat (mycelium)
- Are eukaryotic (bacteria are prokaryotic)
- Require an aerobic environment and a carbon source
- Their natural habitat is the environment, except Candida albicans
What are fungi virulence factors?
1) Capsule – Antiphagocytic. Can be visualized with India ink staining
2) Cell wall - Made of chitin (polysaccharide)
- Some anti-fugal agents work by inhibiting these polysaccharides
3) Cell membrane – Contains ergosterol (human cell membranes contain cholesterol)
- Most antifungal agents work by disrupting ergosterol
Describe yeasts.
- Unicellular form, round or ellipse
- Reproduce by budding – asexual reproduction
- If buds don’t separate, they form long chains of yeast cells called pseudohyphae
Describe molds.
- Multicellular colonies made of clumps of intertwined branching hyphae (mycelia)
- Grow by extending in length
- Produce spores – reproducing bodies of molds
What is dimorphism?
- They form different structures at different temperatures
- They are molds at ambient temperature and yeasts in human tissue at body temperature
How are fungi organized?
- Fungal diseases are organized by the depth of the skin they infect
- Superficial
- Cutaneous
- Subcutaneous
- Systemic
- Opportunistic
What are the superficial fungal infections?
Pityriasis versicolor (tinea versicolor)
Pityriasis versicolor (tinea versicolor) details.
- Etiology: Malassezia furfur
- Occurs more in hot, humid weather, but it is part of normal skin flora
- Physical exam: Hypopigmented or hyperpigmented patches, +/- itching. UV exposure causes skin around patches to tan
- Diagnosis: KOH
- “Spaghetti and meatballs” –> budding yeast (spherical) and hyphae
- Treatments: topical antifungals
- Miconazole cream (Desenex, Zeasorb)
- Topical imidazole (ketoconazole shampoo – Nizoral)
- Selenium sulfide shampoo (Selsun Blue) or zinc shampoo (DHS)
What are the two groups of cutaneous fungal infections?
1) Dermatophytes: Infect Skin, Hair, Nails (karotin)
2) Candida: Infect skin
What fungal infections fall under the Dermatophytes group?
- Trichophyton
- Epidermophyton
- Microsporum
- Tinea corporis - body (red raised border of active inflammation with a healing center)
- Tinea cruris – groin and scrotum
- Tinea pedis – foot
- Tinea capitis – scalp (Primarily in children)
- Tinea unguium (onychomycosis) – nails
What fungal infections fall under the Candida group?
- Candida albicans
- Mouth – Oral thrush: Creamy white exudate on reddish base. Hard to scrape off with tongue blade
- Vagina – Candida vaginitis: Cottage-cheese patches/discharge
- Groin – Diaper rash: SATELLITE LESIONS
What kind of damage can Candida fungi do in immunocompromised individuals?
- Esophagitis: Substernal chest pain, worse with swallowing
- Disseminated (invasive systemic disease): Can invade blood and every organ
How do you diagnose and treat Dermatophytes?
- KOH: branched hyphae
- Culture: hyphae, spores
- Wood’s light: Certain species of Microsporum will fluoresce bright green
- Topical antifungal creams: Terbinefine, miconazole
- Oral agents: Terbinafine, fluconazole, itraconazole
How can Candida fungi be identified and treated?
- Candida is normal flora in the GI tract, vagina, and oropharynx
- Candida in blood is never normal
- KOH of skin
- Stains/culture of tissue
-Treatment: IV antifungal therapy (amphotericin B, fluconazole)
Describe subcutaneous fungal infection.
- Etiologic agent: Sporothrix schenckii (sporotrichosis)
- Normal organism in soil and on plants (ROSE THORNS)
- Enters body after trauma to the skin
- Can stay within skin or can spread along lymphatics to local nodes
- Dimorphic
- Gardeners are at risk
- Forms subcutaneous nodule that becomes necrotic and ulcerated
-Treatment is oral itraconazole (Sproanox)
What are the systemic disease in humans?
1) Histoplasma capsulatum
2) Blastomyces dermatitidis
3) Coccidioides immitis
Describe general characteristics of systemic fungal infections.
- Inhalation of spores from dimorphic fungi
- Normal habitat is soil - grow as mold and release spores into the air
- Within the lungs, spores become yeasts
- Most infections are asymptomatic but can disseminate to other organs
- Not contagious person to person
Histoplasma capsulatum details.
- Mississippi and Ohio rivers
- In soil with BIRD and BAT droppings; nitrogen-rich soil
- Mold spores float from soil to lung alveoli – presents as a pulmonary infection
- Spores get engulfed by macrophages and become yeast
- Most people have silent disease, but it can become disseminated
- Blood, tissue, and urine can be tested
Blastomyces dermatitidis details.
- Mississippi and Ohio river valleys, Great Lakes
- In soil and DECOMPOSING WOOD and LEAVES
- Spores are breathed in and asymptomatic cases are rarely recognized
- Can disseminate to skin and bone
- Diagnosis: biopsy, PCR assay
- Treated with amphotericin B, itraconazole
Coccidioides immitis details.
-Endemic to southwest – AZ, NM, CA, Mexico
“Valley Fever” or “Desert Rheumatism”
-Inhalation of spores from soil
-Become spherules containing endospores in lung
-Local infection of lung is followed by infection of blood –> Usually destroyed at this point by cell-mediated immune system in immunocompetent host
Clinical presentations of Coccidioides immitis.
- Asymptomatic
- Mild URI
- Pneumonia (most mild) – fever, cough, infiltrates on CXR
- Disseminated – spread to brain, bone
- Common opportunistic infection in AIDS patients
Diagnostic of of Coccidioides immitis.
-Skin test like a PPD
-When injected intradermally, an infected person will have a reaction in 1-2 days (delayed hypersensitivity reaction)
Skin test is positive within 2-4 weeks and stays positive for years
-Blood, tissue (biopsy), sputum tests
-Chest x-ray
Treatment of of Coccidioides immitis.
-Amphotericin B, azole antifungals (ketoconazole, itraconazole, fluconazole) for persistent infection or disseminated disease
What are the groups of opportunistic fungal infections and their Etiologic agents?
Cryptococcosis - Cryptococcus neoformans
Aspergillosis - Aspergillus fumigatus
Mucormycosis - Rhizopus species
Pneumocystis jirovecii
Cryptococcosis details.
- Etiologic agent: Cryptococcus neoformans
- Yeast (not dimorphic) with wide capsule
- In soil containing PIGEON droppings
- Inhaled into lungs then can spread to brain via blood
- Most common life-threatening fungal disease in AIDS patients
Disease and diagnostics for Cryptococcosis
Disease can manifest as
1) Lung infection - asymptomatic or can become pneumonia
2) Meningitis - Headache, nausea, confusion, CN deficits
Diagnosis:
- Visualize yeast in spinal fluid – India ink
- Serologic test for antigen and antibody
- Can test spinal fluid for capsular antigens (cryptococcal antigen test) or culture spinal fluid
Aspergillosis details.
- Etiologic agent: Aspergillus fumigatus
- Mold with spores, not dimorphic
- Grows in nature on DECAYING VEGITATION
- Can cause infection of the skin, eyes, ears, and lungs
- Can colonize and invade abraded skin, wounds, burns, eyes, ears, or sinuses
- For lung infections - humans inhale the spores
What are the types of pulmonary disease caused by aspergillosis?
1) ABPA Allergic reaction in airway like asthma: Cough up BROWNISH phlegm containing hyphae
2) Infection in lung: Aspergilloma – fungal ball in lung cavity
3) Invasive lung infection – invasive aspergillosis
Treatment of aspergillosis.
1) Allergic bronchopulmonary aspergillosis:
- Systemic steroids + Oral antifungal agents
2) Aspergilloma
- Surgical removal
3) Invasive aspergillosis –> High mortality
- Antifungal medications
Mucormycosis details
- Etiologic agent: Rhizopus species
- Mold in environment, not dimorphic
- After being inhaled, spores cause blood vessel invasion
- Goes into the blood vessels and clogs it up
- Infarction of tissue distal to blockage
- Sinuses, lungs, gut
Causes opportunistic infection in Diabetics, Burn patients, + Immunocompromised
Treatment: surgery and antifungal medication
Pneumocystis jirovecii details.
In immunocompromised host (AIDS, cancer, organ transplant patients): causes severe pneumonia
- Most common opportunistic infection in AIDS patients*
- Fever, shortness of breath, cough
- Treated with trimethoprim-sulfamethoxazole
- Prophylactic antibiotics are given to prevent this
