Intro to Eukaryotic Pathogens: Part 3 Fungi-Steinauer

Question 1

What are the basic facts of fungi?

Answer 1

Saprophytic: feed on dead/decaying material (need pre-formed organic carbon)
•Mostly aerobic (some facultative anaerobe); no obligate anaerobes
•Candida albicans is considered part of the normal human flora
oImmunocompromised patients
oTreatment difficult

Question 2

What are the properties of the cell wall and membrane of fungi?

Answer 2

oMannoproteins determine serological specificity. Differ in combinations and linkages of polymers
oGlucans: polysaccharides of D-glucose monomers. Function in support of cell wall. Synthesis of ß-glucan is the mechanism of action of the antifungal drug caspofungin
oChitin: Polysaccharide, long chains of N-acetylglucosamine. Support function.
oErgosterols: target of amphotericin B and azole drugs (fluconazole and ketoconazole)

Question 3

What are the two general forms? Describe them.

Answer 3

1. Yeast form
•Unicellular
•Reproduce by budding or fission
•Example: Cryptococcus neoformans
2. Mold/hyphal/filamentous form
•Multicellular
•Mycelium with branches called hyphae.
•Reproduce sexually or asexually
•Conidia: produced by asexual reproduction.
•Spores: produced by sexual reproduction.
•Example: Aspergillus spp.
•Infect the lungs but also skin, eyes and ears.
•Have septates (divisions)
3. Some are dimorphic
•Temperature dependent
•Generally, in humans they are yeast (pathogens) and in environment (cultured) as molds

Question 4

What are the 4 types of lab tests?

Answer 4

1. Microscopic examination
   •10% KOH prep (skin scrapings, sputum, etc)
   •Fungi resistant to alkaline pH
2. Culture
   •Sabouraud’s agar (low pH and antibiotics: inhibits bacteria)
   •Often, VERY slow growth!!
3. DNA based tests
   •ccidioides, Histoplasma, Blastomyces, and Cryptococcus
4. Serologic/immunologic tests
   •Patient’s serum or spinal fluid (for systemic mycoses)

Question 5

Which medical mycoses are described as: •Dermatophytes: Hair, skin, nails.
•Common diseases: ringworm, tinea, athlete’s foot and jock itch.
•Epidermophyton, Trichophyton, and Microsporum
•called “tinea” (tinea capitis, tinea pedis, etc) or “ringworm”
•Infection typically requires direct contact w/ humans or the reservoir.

Answer 5

Cutaneous Mycoses

Question 6

Which medical mycoses are described as: •infection through the skin and then spread, subcutaneous spread, and/or lymphatic spread
•Garderns: thorn prick.
Ex: Sporotrichosis: Sporothrix (rose bushes, plants)

Answer 6

Subcutaneous Mycoses

Question 7

Which medical mycoses are described as: 
•Deep infections of the internal organs
•Mold in soil, yeast in tissues.
•Infection:
•Inhalation of spores into lungs.
•Local infection.
•Dissemination to other organs
Ex: Coccidioides (dimorphic with a spherule)
•Have barrel shape spores.
•In dry environments.
Ex: Histoplasma (dimporphic with macro- and micro-conidia); bird and bat droppings
•Branching structure.
•In river valleys.
•Infect macrophages and are disseminated.

Answer 7

Systemic Mycoses

Question 8

Which medical mycoses are described as:
•Cause infection only in those with reduced defenses
Ex: Candida albicans (oval yeast with pseudohyphae)
Ex: Cryptococcus (wide capsule; pigeon droppings)
•Only has the yeast (spherical) shape.
•Can lead to meningitis.
•Common in AIDS patients.
Ex: Aspergillus – mold and not dimorphic
•Invades abrasions of skin, cornea, sinuses and in lungs.

Answer 8

Opportunistic Mycoses