Fungi (Kinzy) - 5/11/16

Question 1

Describe fungi characteristics (8)

Answer 1

TP DEFENS

Thick rigid walls (barrier to treatment)

Potent Immunogens, source of many allergies

Defense: Mainly neutrophils
Eukaryotic

Form spores: ubiquitous (resilient in environment), airborne

Ergosterol replaces cholesterol in membranes

Neutropenic patients (cancer therapy, transplant recipients) are very susceptible

Saprophytic - secrete enzymes which break down organic matter, transport small molecules back into their cells

Question 2

Anti-fungal drugs

Answer 2

5-fluorocytosine - converted to FdUMP, a dTMP analogue - toxic

Membrane inhibitors

Polyenes - binds ergosterol, disrupts membrane

a. Nystatin (toxic, topical use only)
b. Amphotericin (systemic)

Azoles - inhibit ergosterol synthesis

Pentamidine (vs. Pneumocystis)

Echinocandins (Caspofungin) - inhibit synthesis of cell-wall glucans

Question 3

Life Cycles of Fungi

Answer 3

When we are trying to classify fungal: meiosis = classification

When we are looking into diseases: conidia (asexual spores) = clinical

*REVIEW SLIDE 5

Question 4

Describe fungi classification and requirement.

Answer 4

Based on structures in which meiosis occurs

Requires starvation under specific conditions (almost never seen in clinical samples)

Question 5

What are the four major groups of fungi?

Answer 5

Zygomycetes

Ascomycetes

Basidiomycetes

Fungi imperfecti (no meiotic stage)

Question 6

What are zygomyces?

Answer 6

Growing forms fuse, form a sporangium in which multiple nuclei undergo meiosis

Question 7

What are ascomyces?

Answer 7

4 (or 8) meiotic spores in a sac (ascus)

Diploid nucleus goes through meiosis to produce four haploid nuclei. Each divides again, then forms spore walls around itself. Old cell wall forms a sac (ascus) surrounding the spores.

Question 8

What are basidiomycetes?

Answer 8

Sexual spores bud from tip of club-shaped terminal cell

Question 9

What are fungi imperfecti?

Answer 9

No meiotic stage known.

Really asexual.

Often, a named pathogenic fungus is later found to be the imperfect form of another fungus.

Histoplasma capsulatum = imperfect stage of Allelomyces.

Clinical material is always asexual, so the name of the “imperfect” form is used in medicine.

Question 10

How to identify fungi in the lab?

Answer 10

Culture: not fastidious

Typical: Saboraud agar, broth-based + glucose (simple agar)

Morphology important

Dematiciaceous (pigmented) vs. Hyaline (colorless)

Serology

Treatment may depend more on the site of infection than on the species.

Question 11

How do yeast grow?

Answer 11

Budding yeast: Single cells (spores), grow by budding

Question 12

How does mold grow?

How do pseudohyphae grow?

Answer 12

Cells elongate, form filament (hypha, pl. hyphae)

Mass of hyphae: mycelium (pl. mycelia)

Molds in culture: large fuzzy colonies, often pigmented

Yeast buds elongate, but do not separate; hard to tell from hyphae

TAKEAWAY: growth conditions really affect morphology

Question 13

What are chlamydospores?

Answer 13

Large round terminal cells with thick walls (also pseudohyphae, microconidia)

Question 14

Characteristics of conidia?

Answer 14

Thick-walled resting/dispersal stage

Many different types

• Microcondia (small)
• Macroconidia (hyphae have cross-walls - septa)
• Arthroconidia - alternate cells form thick walls, later hyphae break apart at septa (arthros = joint)
• Phiaoloconidia - chains of conidia bud from specialized terminal cells of hyphae

Question 15

Fungal infections - classified by location?

Answer 15

Superficial: outermost layer of skin, hair (fungi digest keratin)

Cutaneous: confined to skin or mucous membranes

Sub-cutaneous: deeper tissue

Systemic: often start in lung, spread

Primary pathogens vs. opportunists

Question 16

Superficial infection of hair: Piedra

Answer 16

Hyphae grow within hair itself - can cause breaking off of hair… you may see someone with a lot of hair breakage

Question 17

Superficial infection of skin: Tinea

Answer 17

Lesion with inflamed rim of active infection, central clearing

Take specimen from rim (where active infection is occuring - center is usually clear)

Source: soil, animals, humans

Genera: Trichophyton, Epidermophyton, Microsporum

Distinguished by micro- and macroconidia

Seldom need to ID clinically

More common in hot humid climate

Example: Tinea corporis = "Ringworm"
Tinea capitis (if its in your scalp)
- so you could have both... you can use UV lamp to see the rim fluoresce 
Tinea barbae (if it's on your face/neck)
Tinea pedis (feet)
Tinea unguim (onychomycosis... toenail fungus)

Question 18

What are subcutaneous mycoses?

Answer 18

• Fungi introduced by local trauma
• Abscess
• Mycetoma “fungus tumor”
• Similar lesions can be produced by gram (+) Actinomycetes

Question 19

Systemic mycoses (1st 4): common features?

Answer 19

Endemic to specific areas

True pathogens - infect immunocompetent persons

Infection initially in lung - can spread

Exposure often occupational; males > females

Little or no human-to-human transmission

Most infections asymptomatic (liek TB)

Dimorphic:

• Yeast in tissue at 37 degrees Celsius
• Hyphae in standard culture at 30 degrees Celsius

Question 20

Diagnosis?

Answer 20

Microscopy - unique forms in tissue

Skin testing (like TB)

Serology, PCR

Culture

Exoantigen test

Question 21

Blastomyces dermatitidis?

Answer 21

Large yeast w/ broad-based buds

KOH mount (material from tissue emulsified in a drop of concentrated KOH, destroys nearly everything except fungal cell walls)

Question 22

Histoplasma capsulatum?

Answer 22

Tuberculate conidia in culture

In clinical material - tiny intracellular yeast

looks very different in two slides* REVIEW

Question 23

Coccidioides immitis?

Answer 23

Large spherule in lung

Question 24

Paracoccidioides braziliensis?

Answer 24

Yeast with multiple buds = “ship’s wheel”

Question 25

Characteristics of candida albicans?

Answer 25

Budding yeast, hyphae, pseudohyphae, microcnoidia, chlamydospores

Borderline between true pathogen and opportunist

Normal flora

Vaginal infection

GI & skin infections in infants

Oral infection (thrush) - often a sign of compromised cell-mediated immunity (e.g. AIDS)

Question 26

Cryptococcus neoformans?

Answer 26

Heavily-encapsulated yeast
Infections: Lung to brain or meninges
E.g., S. pneumoniae, H. influenzae, N. meningitidis

Question 27

Opportunistic fungal pathogens: Aspergillus

Answer 27

Ubiquitous

Especially in neutropenic patients

Local infection

Lung, can spread to heart or great vessels

Serious infections in neutropenic patients have high mortality rate

Cytokines used to speed recovery of marrow, shorten window of vulnerability

Question 28

Opportunistic fungal pathogens: Zygomycetes - Mucor and Rhizopus

Answer 28

• Nasopharyngeal infections
• Can spread to the brain

Mucor:

• Broad ribbon-like hyphae, lack septa, specimen from heart valve
• Example: Sporangium containing asexual spores

Question 29

Opportunistic fungal pathogens: Pneumocystis carinii

Answer 29

Human isolates also termed P. jirovecii

Ubiquitous

Most people infected in childhood

Rare cause of disease until AIDS epidemic

Major cause of mortality until prophylactic regimens developed

Treatment: Pentamidine, trimethoprim/sulfa.

Considered to be a protozoan until gene sequences showed it to be a yeast

Not possible to culture in clinical labs