Microbiology - Mycology

Question 1

Systemic mycoses

• Examples
• Can cause…
• Caused by/
• Treatment
• Mimic…

Answer 1

• Examples
  
  • Histoplasmosis, Blastomycosis, Coccidioidomycosis, Paracoccidioidomycosis
• Can cause pneumonia and can disseminate.
• Caused by dimorphic fungi
  
  • Cold (20°C) = mold; heat (37°C) = yeast.
  • The only exception is coccidioidomycosis, which is a spherule (not yeast) in tissue.
• Treatment:
  
  • Fluconazole or itraconazole for local infection;
  • Amphotericin B for systemic infection.
• Systemic mycoses can mimic TB (granuloma formation), except, unlike TB, have no person-person transmission.

Question 2

Histoplasmosis

• Location
• Causes…
• Features
• Transmission

Answer 2

• Location
  
  • Mississippi and Ohio River valleys.
• Causes…
  
  • Causes pneumonia.
• Features
  
  • Macrophage filled with Histoplasma (smaller than RBC) [A].
  • Histo hides (within macrophages).
• Transmission
  
  • Bird or bat droppings.

Question 3

Blastomycosis

• Location
• Causes…
• Features

Answer 3

• Location
  
  • States east of Mississippi River and Central America.
• Causes…
  
  • Causes inflammatory lung disease and can disseminate to skin and bone.
• Features
  
  • Forms granulomatous nodules.
  • Broad-base budding (same size as RBC) [B].
    
    • Blasto buds broadly.

Question 4

Coccidioidomycosis

• Location
• Causes…
• Incidence
• Features

Answer 4

• Location
  
  • Southwestern United States, California.
  • “(San Joaquin) Valley fever”
• Causes…
  
  • Causes pneumonia and meningitis
  • Can disseminate to bone and skin.
• Incidence
  
  • Case rate increases after earthquakes (spores in dust are thrown up in the air and become spherules in lungs).
• Features
  
  • Spherule (much larger than RBC) filled with endospores [C].
    
    • Coccidio crowds.
  • “Desert bumps” = erythema nodosum
  • “Desert rheumatism” = arthralgias

Question 5

Paracoccidioidomycosis

• Location
• Features

Answer 5

• Location
  
  • Latin America.
• Features
  
  • Budding yeast with “captain’s wheel” formation (much larger than RBC) [D].
• Paracoccidio parasails with the captain’s wheel all the way to Latin America.

Question 6

Cutaneous mycoses

• Tinea versicolor
  
  • Caused by…
  • Features
  • Treatment
• Other tineae
  
  • Includes…
  • Features

Answer 6

• Tinea versicolor
  
  • Caused by…
    
    • Malassezia furfur.
    • Degradation of lipids produces acids that damage melanocytes and cause hypopigmented and/or hyperpigmented patches.
  • Features
    
    • Occurs in hot, humid weather.
    • “Spaghetti and meatball” appearance [A].
  • Treatment
    
    • Topical miconazole, selenium sulfide (Selsun).
• Other tineae
  
  • Includes…
    
    • Tinea pedis (foot), tinea cruris (groin), tinea corporis (ringworm, on body), tinea capitis (head, scalp), tinea unguium (onychomycosis, on fingernails).
  • Features
    
    • Pruritic lesions with central clearing resembling a ring, caused by dermatophytes (Microsporum, Trichophyton, and Epidermophyton).
    • See mold hyphae in KOH prep, not dimorphic.

Question 7

Examples of opportunistic fungal infections

Answer 7

• Candida albicans
• Aspergillus fumigatus
• Cryptococcus neoformans
• Mucor and Rhizopus spp.
• Pneumocystis jirovecii
• Sporothrix schenckii

Question 8

Candida albicans

• Features
• Causes…
• Treatment

Answer 8

• Features
  
  • alba = white.
  • Systemic or superficial fungal infection.
• Causes…
  
  • Oral and esophageal thrush in immunocompromised (neonates, steroids, diabetes, AIDS), vulvovaginitis (diabetes, use of antibiotics), diaper rash, endocarditis in IV drug users, disseminated candidiasis (to any organ), chronic mucocutaneous candidiasis.
• Treatment
  
  • Topical azole for vaginal
  • Fluconazole or caspofungin for oral/esophageal
  • Ffluconazole, amphotericin B, or caspofungin for systemic.

Question 9

Aspergillus fumigatus

• Features
• Causes…

Answer 9

• Features
  
  • Invasive aspergillosis, especially in immunocompromised and those with chronic granulomatous disease.
  • Not dimorphic.
• Causes…
  
  • Allergic bronchopulmonary aspergillosis (ABPA)
    
    • Associated with asthma and cystic fibrosis
    • May cause bronchiectasis and eosinophilia.
  • Aspergillomas in lung cavities, especially after TB infection.
  • Some species of Aspergillus produce aflatoxins, which are associated with hepatocellular carcinoma.
  • Think “A” for Acute Angles in Aspergillus.

Question 10

Cryptococcus neoformans

• Causes…
• Features
• Transmission
• Diagnosis
  *

Answer 10

• Causes…
  
  • Cryptococcal meningitis, cryptococcosis.
• Features
  
  • Heavily encapsulated yeast.
  • Not dimorphic.
  • “Soap bubble” lesions in brain.
• Transmission
  
  • Found in soil, pigeon droppings.
  • Acquired through inhalation with hematogenous dissemination to meninges.
• Diagnosis
  
  • Culture on Sabouraud agar.
  • Stains with India ink and mucicarmine.
  • Latex agglutination test detects polysaccharide capsular antigen and is more specific.

Question 11

Mucor and Rhizopus spp.

• Causes…
• Features
• Treatment

Answer 11

• Causes…
  
  • Mucormycosis.
  • Disease mostly in ketoacidotic diabetic and leukemic patients.
  • Rhinocerebral, frontal lobe abscesses.
  • Headache, facial pain, black necrotic eschar on face
  • May have cranial nerve involvement.
• Features
  
  • Fungi proliferate in blood vessel walls when there is excess ketone and glucose, penetrate cribriform plate, and enter brain.
• Treatment
  
  • Amphotericin B.

Question 12

Pneumocystis jirovecii

• Causes…
• Features
• Transmission
• Diagnosis
• Treatment/prophylaxis

Answer 12

• Causes…
  
  • Pneumocystis pneumonia (PCP), a diffuse interstitial pneumonia.
  • Immunosuppression (e.g., AIDS) predisposes to disease.
• Features
  
  • Yeast (originally classified as protozoan).
  • Most infections are asymptomatic.
• Transmission
  
  • Inhaled.
• Diagnosis
  
  • Diffuse, bilateral CXR appearance.
  • Diagnosed by lung biopsy or lavage.
  • Disc-shaped yeast forms on methenamine silver stain of lung tissue [A].
• Treatment/prophylaxis
  
  • TMP-SMX, pentamidine, dapsone (prophylaxis only), atovaquone (prophylaxis only).
  • Start prophylaxis when CD4 count drops < 200 cells/mm3 in HIV patients.

Question 13

Sporothrix schenckii

• Causes…
• Features
• Transmission
• Treatment

Answer 13

• Causes…
  
  • Sporotrichosis.
  • Little systemic illness.
• Features
  
  • Dimorphic, cigar-shaped budding yeast that lives on vegetation [A].
• Transmission
  
  • 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).
• Treatment
  
  • Itraconazole or potassium iodide.
• “Plant a rose in the pot.”