Mycology

Question 1

• Types of fungi?
• Habitat?

Answer 1

Two types of fungi:

• Yeast - single cell
• Mold - long hyphae and form a mat

Fungi are:

• Eukaryotic (bacteria are prokaryotic)
• Obligate aerobe

Habit is environment, exception is Candida albicans (human host)

Question 2

Fungi virulence factors

• What are the cell wall and membrane made of?
• Clinical significance?

Answer 2

Fungi virulence factors

• Capsule - antiphagocytic
• Cell wall made of chitin polysaccharide (not peptidoglycan so abx does not work)
• Cell membrane contains ergosterol - most antifungals work by disrupting ergosterol

Question 3

What is the clinical significance of fungi being dimorphic?

Answer 3

Many fungi are dimorphic

• These fungi can grow TWO different way (e.g. Valley Fever)
• Form different structures at different temperatures

Question 4

Pityriasis versicolor (Tinea versicolor)

Answer 4

Pityriasis versicolor (Tinea versicolor) = superficial infection, pigment change, spaghetti & meatballs, wrestlers, yogis, surfers

• Hypo or hyperpigmented
• About the volume you have been exposed to
• UV exposure causes skin around patches to tan
• Dx with KOH prep

Question 5

Cutaneous fungal infections

• Known as?
• Affects?
• Most important ones?
• How to dx?

Answer 5

Cutaneous fungal infections

• Known as the dermatophytoses
• Skin, hair, nails
  
  • Pruritic
  • Broken hairs
  • Damaged nails
  • Inflamed circular border with central clearing
• Most important ones:
  
  • Trichophyton
  • Epidermophyton
  • Microsporum (ring worm)
• Diagnosis
  
  • KOH
  • Branched hyphae (as opposed to spaghetti and meatballs)

Question 6

Cutaneous fungal infections: dermatophytoses

What are all the names according to location on body?

Answer 6

Cutaneous fungal infections: dermatophytoses

• Tinea corporis - body
• Tinea cruris - jock itch
• Tinea pedis - athlete’s foot
• Tinea capitis - scalp (common in children)
• Tina unguium - onychomycosis

Question 7

Candida albicans

Answer 7

Candida albicans = cutaneous infection, thrush, candida vaginitis, diaper rash (satellite lesions), immunocompromised patients, after abx

• Lives in humans, not the environment
• Oral thrush
  
  • Creamy, white exudate
  • Hard to scrape off with tongue depressor
  • Tx is “swish and spit”
• Candida vaginitis
  
  • Cottage cheese discharge
• Diaper rash
  
  • Satellite lesions
• Immunocompromised patients
  
  • Fungus in blood

Question 8

Sprothrix schenckii (sporotrichosis)

Answer 8

Sprothrix schenckii (sporotrichosis) = subcutaneous infection, rose thorns, gardeners, dimophic

• Lives in soil and on plants
• Enters body after trauma
• Dimorphic - yeast at high temps and branching hyphae at lower temps

Question 9

Systemic fungal infections

• 3 types
• How do you get infection?

Answer 9

Systemic fungal infections = NOT contagious person to person

• 3 types:
  
  • Histoplasma capsulatum
  • Blastomyces dermatitidis
  • Coccidioides immitis
• Inhalation of dimorphic fungi spores
• Breathe in spores from soil and they go from mold to yeast

Question 10

Histoplasma capsulatum

Answer 10

Histoplasma capsulatum = histoplasmosis, bats and bridges

• Causes histoplasmosis
• Mississippi and Ohio rivers
• Grows in soil that is contaminated with bird and bat droppings

Question 11

Blastomyces dermatitidis

Answer 11

Blastomyces dermatitidis = blastomycosis, rivers and lakes

• Causes blastomycosis
• Mississippi and Ohio rivers, and Great Lakes
• Grows in soil, wood, and leaves

Question 12

Coccidioides immitis / coccidioidomycosis

Answer 12

Coccidioides immitis / coccidioidomycosis = Valley Fever, erythema nodosum (rash), granulomas on CXR, opportunistic infection

• AZ, CA, NM, Mexico
• Aka Desert Rheumatism
• Can present clinically as:
  
  • Asymptomatic
  • URI / flu
  • Pneumonia
  • Erythema nodosum (rash)
  • Granuloma on CXR

Question 13

Cryptococcosis

Answer 13

Cryptococcosis = pigeons, opportunistic infection, most common life threatening fungal dz in AIDS patients, meningitis

• Crytococcus neoformans
• Yeast, not dimorphic
• Found in soil with pigeon droppings
• Disease can manifest as:
  
  • Lung infection
  • Meningitis (cryptococcal meningitis)

Question 14

Aspergillosis

Answer 14

Aspergillosis = decaying vegetation, opportunistic infection, asthma like symptoms

• Aspergillus fumigatus
• Mold with spores, not dimorphic
• Grows in nature on decaying vegetation
• Can cause infection of skin, eyes, ears, and lungs
• Allergic reaction in airway like asthma
• Allergic bronchopulmonary aspergillosis (ABPA)
• Cough up brown phelgm containing hyphae

Question 15

Mucormycosis

Answer 15

Mucormycosis = cause blood vessel invasion, infarction of tissue distal to blockage (will eat away at brain), opportunistic infection

• Rhizopus species
• Mold in environment, not dimorphic

Question 16

Pneumocystis jirovecii

Answer 16

Pneumocystis jirovecii = PCP, most common opportunistic infection in AIDS patients, tx with Bactrim, those on Prednisone at risk, prophylactic abx given

• Yeast
• In normal host: lives in lung without causing problems
• In immunocompromised host:
  
  • Causes severe pneumonia
  • PCP - pneumocytosis carinii pneumonia