Fungi (Kinzy) - 5/11/16 Flashcards
Describe fungi characteristics (8)
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
Anti-fungal drugs
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
Life Cycles of Fungi
When we are trying to classify fungal: meiosis = classification
When we are looking into diseases: conidia (asexual spores) = clinical
*REVIEW SLIDE 5
Describe fungi classification and requirement.
Based on structures in which meiosis occurs
Requires starvation under specific conditions (almost never seen in clinical samples)
What are the four major groups of fungi?
Zygomycetes
Ascomycetes
Basidiomycetes
Fungi imperfecti (no meiotic stage)
What are zygomyces?
Growing forms fuse, form a sporangium in which multiple nuclei undergo meiosis
What are ascomyces?
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.
What are basidiomycetes?
Sexual spores bud from tip of club-shaped terminal cell
What are fungi imperfecti?
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.
How to identify fungi in the lab?
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.
How do yeast grow?
Budding yeast: Single cells (spores), grow by budding
How does mold grow?
How do pseudohyphae grow?
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
What are chlamydospores?
Large round terminal cells with thick walls (also pseudohyphae, microconidia)
Characteristics of conidia?
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
Fungal infections - classified by location?
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
Superficial infection of hair: Piedra
Hyphae grow within hair itself - can cause breaking off of hair… you may see someone with a lot of hair breakage
Superficial infection of skin: Tinea
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)
What are subcutaneous mycoses?
- Fungi introduced by local trauma
- Abscess
- Mycetoma “fungus tumor”
- Similar lesions can be produced by gram (+) Actinomycetes
Systemic mycoses (1st 4): common features?
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
Diagnosis?
Microscopy - unique forms in tissue
Skin testing (like TB)
Serology, PCR
Culture
Exoantigen test
Blastomyces dermatitidis?
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)
Histoplasma capsulatum?
Tuberculate conidia in culture
In clinical material - tiny intracellular yeast
looks very different in two slides* REVIEW
Coccidioides immitis?
Large spherule in lung
Paracoccidioides braziliensis?
Yeast with multiple buds = “ship’s wheel”
Characteristics of candida albicans?
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)
Cryptococcus neoformans?
Heavily-encapsulated yeast
Infections: Lung to brain or meninges
E.g., S. pneumoniae, H. influenzae, N. meningitidis
Opportunistic fungal pathogens: Aspergillus
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
Opportunistic fungal pathogens: Zygomycetes - Mucor and Rhizopus
- Nasopharyngeal infections
- Can spread to the brain
Mucor:
- Broad ribbon-like hyphae, lack septa, specimen from heart valve
- Example: Sporangium containing asexual spores
Opportunistic fungal pathogens: Pneumocystis carinii
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
