MCM 2-41 Pathogenic Fungi Flashcards
what is the main issue with fungi treatment?
we are more similar to fungi than we are to bacteria. there is a lot of “toxic spillover” with antifungal medications that can effect those similar structures in humans
hardiness of bacteria vs fungi
fungi can grow in colder, dried, more acidic, and more osmotically hihg pressure areas (high osmotic pressure jelly in the fridge growing mold)
two major types of fungi
Yeast - simple single cells, reproduce via budding
mold - more complicated, grow as filaments (hyphae) and form mat (mycelium). growth occurs at tip of filament. asexual and sexual structures
both do mitosis
fungi undergo mitosis (TF)
True - however fungi undergo a “closed” mitosis meaning that the nuclear envelope does not disperse - harder to see in microscope
sexual or asexual molds are more clinically relevant?
what is important for microscopic diagnosis?
asexual molds
distinct appearance of spores
prokaryotes are ___ by definition, fungi are ______
prokaryotes are bacteria
fungi are eukaryotic heterotrophs like humans
What must antifungals target? why?
fungi do not have 70s ribosomes or peptidoglycan walls
antifungals must target beta-glucan walls and ergosterol in the membrane
TF Antifungals often have some toxicity in humans, and there are many fewer molecular targets available
true - many of their molecules are too similar to ours
why are there more cutaneous fungal infections and food spoilage?
fungi can live in the fridge and survive on the hostile enrivonment of the skin because they can can grow in drier, higher-osmotic-pressure, and colder environments than bacteria
five types of asexual spores, called ____, have what?
conidia
distinctive microscopic appearances used for diagnosis
Thermal dimorphism
: several important fungal pathogens grow as mold at 24C and as yeast at 37C. Yeast form has more immune-evasive properties; dual cultures can be useful for diagnosis.
immune response to fungal infection?
granulomatous, sometime also suppurative (pus forming and discharge)
most fungal pathoens are…
environmental - little contagion or drug resistance, no eradication
Exception: C. albicans yeast is normal flora / opportunistic pathogen
Mycotoxicosis
caused by eating fungal toxins (wrong mushroom or spoiled food); not fungal infection.
fungal infection can be diagnosed by
PPD, KOH-mount microscopy with fungal stains, culture on Sabouraud’s agar.
major classes of antifungals
are polyenes (disrupt fungal cell membranes at ergosterol insertion sites), azoles (inhibit ergosterol synthesis), echinocandins (inhibit beta-glucan synthesis)
polyenes what do they do? toxicity? examples? treats which fungi?
disrupt cell wall membranes at ergosterol insertion sites
highly effective and broad-spectrum but toxic – Amphotericin B is the only systemic and is nephrotoxic
azoles what do they do? toxicity? examples? treats which fungi?
inhibit ergosterol synthesis
are less toxic; different ones optimally active against different fungi; Fluconazole/Diflucan major one, treats candidiasis and cryptococcosis
Echinocandins what do they do? toxicity? examples? treats which fungi?
inhibit beta glucan synthesis
are low-toxicity, highly effective against candida and aspergillus
examples end in “-fungin”
superficial mycoses
symptoms?
treatment?
caused by fungal grown on superficial skin layer. does not require thermal dimorphism
very common - symptoms are minor; itch or discoloration. treated with topical azoles (fluconazole, diflucan)
fluconAZOLE
dermatophytosis
example?
symptoms called? tranmitted by? diagnosed with? treatment? thermal dimorphism?
example of superficial mycoses
athletes foot - “dermatophytosis” caused by three different fungi genera
infect only superficial keratinized structures via keratinases
symptoms are called tinea
transmitted by fomites or autoinnoculation
diagnose with KOH mount, culture
treat all body sites simultaneously with topical azole
subcutaneous mycoses
spread pattern?
thermal dimoprhism?
history of?
treatment
introduced by trauma exposing subcuntenous tissue to soil or vegetation.
slow spread from trauma site towards trunk by lymphatics
-thermal dimorphism
history of ineffective antibiotic treatment
treatment with oral azoles.
serioues cases may require amphotericin B and local surgery
sporotrichosis
thermal dimorphism?
transmission?
spreading?
diagnose?
treatments?
example of subcutaneous mycoses
caused by sporothrix spp
thermal dimosphism
enters skin through small injuries like throns/splinters
painless ulcer at site spreads up lymphatics over years
if immunocompromised - may be dissemintated meningitis
diagnose biospy and culture at room temp from pus (turn it from yeast form to mold form)
treat normal type with oral azoles
more serious forms with amphotericin B
Systemic Mycoses
tramission?
thermal dimosphism?
severity?
problem?
these are environmental spores/fungi in soil that get inhaled into the lungs. not person to person
thermal dimorphism
range of severity - asymptomatic to death
may mimic TB, but source is american dirt not foriegn crowds
