Fungi Flashcards
What are Fungi?
unlike bacteria - they are eukaryotes and posses a nuclear membrane and membrane bound organelles, such as endoplasmic reticulum and mitochondria
what do fungi look like?
- plant-like forms but lack defined root or leaf structures and are non-photosyntheitic
what is their kingdom?
they are assigned their own - Mycota
what are Yeast forms?
single, unconnected vegetative cells which grow in a manner similar to bacteria (but they grow ten times faster)
How do Yeast reproduce?
by budding
What don’t Yeast do?
they do not sporulate and are not much of a hazard to lab workers
What are filamentous fungi (/molds)?
consist of a complex mass (mycelium) composed of tubes called hyphae
How do hyphae reproduce?
by the formation of spores which are released in enormous numbers from the mycelium
What happens to these spores?
can become airborne and present a contamination hazard in labs working on pathogenic molds
How can spores be formed?
asexually or sexually
asexually - most common way and are called Conidia
Sexual = ascospores
What happens when the hyphal filaments are packed densely?
the mycelium can appear to be cohesive tissue, as in the case of mushrooms
what do Fungi produce?
Fungi are saprophytic or parasitic and procude a variety of unusual metabolic products, some of which are highly toxic to higher animals
How do you identify fungi?
Medically important fungi = ID depends upon microscopic examination of the morphology, particularly of sporulating forms “by their fruits ye shall know them”
- biochemical tests / sophisticated technologies can also be used
What are dimorphic fungi?
fungi which have both yeast and filamentous phases, usually dependent on temperature or other growth conditions
Taxonomy: why is the classification of fungi difficult?
complicated because many fungi can reproduce both sexually and asexually
= the morphological charactristics are different for each stage, and since speciation was established on the microscopic morphology, the sexual and asexual stages of teh same ogranism may actually have different species names
Taxonomy: Asexual stage name?
anamorphic
- asexual = budding
- a group of fungi which only an anamorphic (asexual) form is known and these are termed the Fungi Imperfecti
Taxonomy: why called fungi imperfecti?
because they reproduce in a non-sexual manner and God declares sexual is the perfect / correct way of producing
Taxonomy: Sexual stage name?
telomorphic
For clinical purposes how can fungi be classified?
into: yeasts, molds, dimorphic fungi and poisonous mushrooms
What is a kerion?
a large mat of fungal infection
what is jock itch caused by?
Trichophyton mentagrophytes
Athletes foot is caused by what?
dermatophytes - and the resulting skin fissuring may predispose infected patients to bacterial cellulitis
most yeast infections are what?
endogenous - except for Cryptococcus neoformans - which is associated wiht teh excreta of gregarious birds - primarily pigeons
What are the Predisposing Factors to Yeast infection? (Superficial)
1) wet work (dishwashers)
2) pregnancy, oral contraceptives (tight clothing)
3) diabetes mellitus
4) use of broad spectrum antibiotics
5) HIV infection, CD4 < 500
6) Dectin-1 (beta glucan receptor deficiency)
What are the Predisposing Factors to Yeast infection? (Deep)
1) immunosuppression, especially corticosteroids
2) indwelling venous catheters
3) use of broad spectrum antibiotics
4) IV drug abuse
5) HIV infection, with CD4 < 200 ** (big point to remember)
Diagnosis of Yeast
- microscopic examination with quick wetmount establishes the presence of yeast since they are much larger than bacteria
next step: germ tube test which is speciifc for Candida albicans - yeast is incubated for three hours at 37 degrees in a biological fluid
Formation of germ tubes provides what?
definitive identification - if psoitive - no further tests are necessary
negative - yeast is planted on corn meal agar and examined after incubation
What other tests may be necessary for yeast?
biochemical and carbohydrate assimilation tests may also be necessary
Whats good about the germ tube test?
- any lab anywhere can do this - very simple
Positive = candida albicans
Candida Albicans
extremely common - part of the normal flora of the oropharynx, vagina, bowel, and skin
- most common species causing infection
in normal individuals - what does CA cause?
mild to severe or even chronic superficial infections of the skin - due to wet skin on skin (sweaty) = red patch, bit of a silvery shine under some light
KEY FEATURE = satellte lesion = little ones outside the main patch
What are some examples of the superficial infections CA can cause?
(diaper rash, balanitis, infections of intertriginous areas), nails (onchomycosis) and mucous membranes (thrush - white patches in back of mouth, and vaginitis - cottage cheese-like discharge)
in immunocompromised patients, what happens?
deep tissues can be infected to produce severe systemic disease (esophagitis, pyelonephritis, sepsis)
t
Therapy ?
topical
vaginal = swallow fluconazole once and its done
Cryptococcus neoformans var neoformans
get from being around birds
what does neoformans cause?
- diffuse pulmonary infection - usually asymptomatic - but can also cause localized abseccess and granuloma formation in lung, brain, lymph nodes, skin and bone
- mainly associated with chronic meningitis in AIDS patients
Cryptococcus Gattii
- causes localized abscesses (cryptococcomata) in the tropics
- associated with eucalyptus plants
- emerging problem in Pacific NW where it colonized in trees and soil
- 20% mortality, most commonly pneumonia, and most patients not immunocompromised
