Microbiology- Micology

Question 1

Systemic mycoses

Answer 1

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.

Question 2

Histoplasmosis

• ENDEMIC LOCATION
• PATHOLOGIC FEATURES
• UNIQUE SIGNS/SYMPTOMS
• DIAGNOSIS

Answer 2

• Mississippi and Ohio River Valleys
• Macrophage filled with Histoplasma (smaller than RBC)
• Palatal/tongue ulcers, splenomegaly
• Diagnosis via urine/ serum antigen

Question 3

Blastomycosis

• ENDEMIC LOCATION
• PATHOLOGIC FEATURES
• UNIQUE SIGNS/SYMPTOMS

Answer 3

• 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

Question 4

Coccidioidomycosis

• ENDEMIC LOCATION
• PATHOLOGIC FEATURES
• UNIQUE SIGNS/SYMPTOMS

Answer 4

• 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

Question 5

Paracoccidioidomycosis

• ENDEMIC LOCATION
• PATHOLOGIC FEATURES
• UNIQUE SIGNS/SYMPTOMS

Answer 5

• Latin America
• Budding yeast of Paracoccidioides with “captain’s wheel” formation (much larger than RBC).
• Similar to blastomycosis, males > females

Question 6

Cutaneous mycoses

Answer 6

Tinea (dermatophytes), Tinea (pityriasis) versicolor,

Question 7

Tinea (dermatophytes)

Answer 7

Dermatophytes include Microsporum, Trichophyton, and Epidermophyton. Branching septate hyphae visible on KOH preparation with blue fungal stain. Associated with pruritus.

Question 8

Tinea corporis

Answer 8

Occurs on torso. Characterized by erythematous scaling rings (“ringworm”) and central clearing. Can be acquired from contact with an infected cat or dog.

Question 9

Tinea pedis

Answer 9

Three varieties:
Interdigital; most common
Moccasin distribution
Vesicular type

Question 10

Tinea (pityriasis) versicolor

Answer 10

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.

Question 11

Opportunistic fungal infections

Answer 11

Candida albicans, Aspergillus fumigatus, Cryptococcus

neoformans, Mucor and Rhizopus spp., Pneumocystis jirovecii,

Question 12

Candida albicans characteristics and treatment

Answer 12

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.

Question 13

Candida albicans disease

Answer 13

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.

Question 14

Aspergillus fumigatus Characteristics and disease

Answer 14

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).

Question 15

Allergic bronchopulmonary aspergillosis (ABPA)

Answer 15

hypersensitivity response associated with asthma and cystic fibrosis; may cause bronchiectasis and eosinophilia.

Question 16

Cryptococcus neoformans Characteristics and Diagnosis

Answer 16

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.

Question 17

Cryptococcus neoformans Disease and Treatment

Answer 17

Causes cryptococcosis, cryptococcal meningitis, 
 ryptococcal encephalitis (“soap bubble” lesions in brain), primarily in immunocompromised.

Treatment: amphotericin B + flucytosine followed by fluconazole for cryptococcal meningitis.

Question 18

Mucor and Rhizopusm spp. Characteristics and Treatment

Answer 18

Irregular, broad, nonseptate hyphae branching at wide angles.

Treatment: surgical debridement, amphotericin B or isavuconazole.

Question 19

Mucor and Rhizopusm spp. Disease

Answer 19

Causes mucormycosis, mostly in ketoacidotic diabetic and/or neutropenic patients (eg, leukemia). Inhalation of spores Žfungi 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.

Question 20

Pneumocystis jirovecii Characteristics and disease

Answer 20

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.

Question 21

Pneumocystis jirovecii Treatment and Diagnosis

Answer 21

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.

Question 22

Sporothrix schenckii Characteristics and treatment

Answer 22

Dimorphic, cigar-shaped budding yeast that grows in branching hyphae with rosettes of conidia; lives on vegetation.

Treatment: itraconazole or potassium iodide.

Question 23

Sporothrix schenckii Disease

Answer 23

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.