Microbiology- Micology Flashcards
Systemic mycoses
Histoplasmosis, Blastomycosis, Coccidioidomycosis, Paracoccidioidomycosis.
All of the following can cause pneumonia and can disseminate.
All are caused by dimorphic fungi: cold (20°C) = mold; heat (37°C) = yeast. Only exception is Coccidioides, which is a spherule (not yeast) in tissue. Systemic mycoses can form granulomas.
Treatment: fluconazole or itraconazole for local infection; amphotericin B for systemic infection.
Histoplasmosis
- ENDEMIC LOCATION
- PATHOLOGIC FEATURES
- UNIQUE SIGNS/SYMPTOMS
- DIAGNOSIS
- Mississippi and Ohio River Valleys
- Macrophage filled with Histoplasma (smaller than RBC)
- Palatal/tongue ulcers, splenomegaly
- Diagnosis via urine/ serum antigen
Blastomycosis
- ENDEMIC LOCATION
- PATHOLOGIC FEATURES
- UNIQUE SIGNS/SYMPTOMS
- Eastern and Central US
- Broad-based budding of Blastomyces (same size as RBC)
- Inflammatory lung disease, can disseminate to skin/
bone. Verrucous skin lesions can simulate SCC. Forms granulomatous nodules
Coccidioidomycosis
- ENDEMIC LOCATION
- PATHOLOGIC FEATURES
- UNIQUE SIGNS/SYMPTOMS
- Southwestern US, California
- Spherule (much larger than RBC) filled with endospores of Coccidioides
- Disseminates to skin/ bone. Erythema nodosum (desert bumps) or multiforme. Arthralgias (desert
rheumatism) . Can cause meningitis
Paracoccidioidomycosis
- ENDEMIC LOCATION
- PATHOLOGIC FEATURES
- UNIQUE SIGNS/SYMPTOMS
- Latin America
- Budding yeast of Paracoccidioides with “captain’s wheel” formation (much larger than RBC).
- Similar to blastomycosis, males > females
Cutaneous mycoses
Tinea (dermatophytes), Tinea (pityriasis) versicolor,
Tinea (dermatophytes)
Dermatophytes include Microsporum, Trichophyton, and Epidermophyton. Branching septate hyphae visible on KOH preparation with blue fungal stain. Associated with pruritus.
Tinea corporis
Occurs on torso. Characterized by erythematous scaling rings (“ringworm”) and central clearing. Can be acquired from contact with an infected cat or dog.
Tinea pedis
Three varieties:
Interdigital; most common
Moccasin distribution
Vesicular type
Tinea (pityriasis) versicolor
Caused by Malassezia spp. (Pityrosporum spp.), a yeast-like fungus. Degradation of lipids produces acids that damage melanocytes and cause hypopigmented, hyperpigmented, and/or pink patches. Less pruritic than dermatophytes.
“Spaghetti and meatballs” appearance on microscopy.
Treatment: selenium sulfide, topical and/or oral antifungal medications.
Opportunistic fungal infections
Candida albicans, Aspergillus fumigatus, Cryptococcus
neoformans, Mucor and Rhizopus spp., Pneumocystis jirovecii,
Candida albicans characteristics and treatment
Dimorphic; forms pseudohyphae and budding yeasts at 20°C A , germ tubes at 37°C B .
Treatment: oral fluconazole/topical azole for vaginal; nystatin, fluconazole, or echinocandins for
oral/esophageal; fluconazole, echinocandins, or amphotericin B for systemic.
Candida albicans disease
Systemic or superficial fungal infection. Causes oral and esophageal thrush in immunocompromised (neonates, steroids, diabetes, AIDS), vulvovaginitis (diabetes, use of antibiotics), diaper rash, endocarditis (IV drug users), disseminated candidiasis (especially in neutropenic patients), chronic mucocutaneous candidiasis.
Aspergillus fumigatus Characteristics and disease
Monomorphic septate hyphae that branch at 45° Acute Angle.
Causes invasive aspergillosis in immunocompromised patients, neutrophil dysfunction (eg, chronic granulomatous disease). Can cause aspergillomas in pre-existing lung cavities, especially after TB infection.
Some species of Aspergillus produce Aflatoxins (associated with hepatocellular carcinoma).
Allergic bronchopulmonary aspergillosis (ABPA)
hypersensitivity response associated with asthma and cystic fibrosis; may cause bronchiectasis and eosinophilia.
Cryptococcus neoformans Characteristics and Diagnosis
5–10 μm with narrow budding. Heavily encapsulated yeast. Not dimorphic
Found in soil, pigeon droppings. Acquired through inhalation with hematogenous dissemination to meninges.
Culture on Sabouraud agar. Highlighted with India ink (clear halo G) and mucicarmine (red inner capsule H). Latex agglutination test detects polysaccharide capsular
antigen and is more specific.
Cryptococcus neoformans Disease and Treatment
Causes cryptococcosis, cryptococcal meningitis, ryptococcal encephalitis (“soap bubble” lesions in brain), primarily in immunocompromised.
Treatment: amphotericin B + flucytosine followed by fluconazole for cryptococcal meningitis.
Mucor and Rhizopusm spp. Characteristics and Treatment
Irregular, broad, nonseptate hyphae branching at wide angles.
Treatment: surgical debridement, amphotericin B or isavuconazole.
Mucor and Rhizopusm spp. Disease
Causes mucormycosis, mostly in ketoacidotic diabetic and/or neutropenic patients (eg, leukemia). Inhalation of spores fungi proliferate in blood vessel walls, penetrate cribriform plate, and enter brain. Rhinocerebral, frontal lobe abscess; cavernous sinus thrombosis. Headache, facial pain, black necrotic eschar on face; may have cranial nerve involvement.
Pneumocystis jirovecii Characteristics and disease
Yeast-like fungus (originally classified as protozoan). Most infections are asymptomatic.
Causes Pneumocystis pneumonia (PCP), a diffuse interstitial pneumonia. Immunosuppression (eg, AIDS) predisposes to disease. Diffuse, bilateral ground-glass opacities on CXR/CT, with pneumatoceles.
Pneumocystis jirovecii Treatment and Diagnosis
Treatment/prophylaxis: TMP-SMX, pentamidine, dapsone (prophylaxis only), atovaquone. Start prophylaxis when CD4+ count drops to < 200 cells/mm3 in HIV patients.
Diagnosed by lung biopsy or lavage. Disc-shaped yeast seen on methenamine silver stain of lung tissue.
Sporothrix schenckii Characteristics and treatment
Dimorphic, cigar-shaped budding yeast that grows in branching hyphae with rosettes of conidia; lives on vegetation.
Treatment: itraconazole or potassium iodide.
Sporothrix schenckii Disease
When spores are traumatically introduced into the skin, typically by a thorn (“rose gardener’s disease”), causes local pustule or ulcer with nodules along draining lymphatics (ascending lymphangitis). Disseminated disease possible in immunocompromised host.
