mycology

why are fungi important to learn about even though they are less common pathogens than bacteria? what kinds of infections do they cause?
fungi are capable of very severe and rapidly fatal infections. they are opportunistic and nosocomial pathogens (4-5th leading cause of which), meaning they often cause infection in previously infected pts
what is one reason fungi are increasing as opportunistic and nosocomial pathogens?
antibiotics limit bacterial infection but favor fungal infections, many immunocompromised people are living longer, due to HIV, organ transplants
why are fungal infections often life threatening or fatal?
the host is usually already compromised, they are often misdiagnosed, the illness progresses rapidly, and there is a lack of safe and effective antifungals
are fungi eu- or prokaryotic?
fungi are eukaryotic with a nuclear membrane around their nuclei, and have subcellular organelles such as mitochondria, ribosomes, ER, golgi, and microtubules.
what is the plasma membrane of fungi called? what is it composed of? what about the cell wall?
the fungal plasma membrane or plasmalemma is composed of glycoproteins, lipids and ergosterol, (unique to fungi, mammals have cholesterol). the cell wall, which is unique to fungi is composed of chitin, (polymer of N-acetyl glucosamine), mannans, glucans, and other complex carbohydrates
how do the cell types of bacteria and fungi compare? plasma membranes? cell walls? reproduction models?
fungi are eukaryotic, bacteria are prokaryotic. fungi have ergosterol in their plasma membrane, bacteria have no sterols. fungal cell walls have chitin, mannans, and glucans, bacteria have peptidoglycan, techoic acids, and LPS. fungi can reproduce via sexual and asexual spores, and budding/fission, bacteria can only replicate via binary fission
what are the different kinds of fungi?
mold, (filamentous), yeast, (oval, single-celled), dimorphic fungi, (mold in nature, yeasts in tissue- due to temp), and dematiaceous fungi, (black/brown pigmented – seen more as opportunistic pathogens causing phaeohyphomycosis)
how can you tell yeast cells from bacterial cocci?
yeast cells are larger
wha are hyphae? what are they called with septa and without?
hyphae are filaments or tubular structures of molds. hyphae with cross walls, (septae) are septated, (aspergillus). hyphae without septae are nonseptated or cocnocytic, (zygomycetes). allows these 2 infections, which are similar to be discerned
what are pseudohyphae?
hyphae-like structures formed by incomplete budding of yeast cells, that are constricted at their point of attachment, (seen in candidia albicans)
what is mycelium? what are the vegetative and aerial mycelium
a mass of intertwined hyphae. vegetative mycelium absorb nutrients and aerial mycelium contain reproductive structures, asexual spores called conidia, (and their support chains: conidiophores), and sporangiospores within sporangium seen in nonseptated fungi
what fungi have condiphores vs sporangium?
aspergillus has condiphores which stick out vs zygomycetes which usually has sporangium that are held closer in
what are blastoconidia?
a type of conidia that is an asexual budding yeast cell. these can be seen in dimorphic fungi.
what are microconidia/macroconidia?
single or multi-celled conida that are used to ID/speciate dermatophytes, (ringworm, tinea)
what are arthroconidia? what function do they perform?
arthroconidia are the infectious form of coccidiodes immitis. these conidia are formed by the fragmentation of hyphae, (asexual spores).
what are endospores? where are they produced?
endospores and are produced within a spherules, the asexual tissue form of coccidiodes immitis
what is a fungal form producing sexual spores called?
telemorph
what is a fungal form producing asexual spores called?
anamorph
what are the three kinds of sexual spores?
ascospores, basidiospores and zygospores
what is the classification for fungi whos sexual state is unknown?
deuteromycetes/fungi imperfecti
what form are deuteromycetes with both a telomorphic and anamorphic form usually seen as, and thus referred to?
their anamorphic/asexual form
are cutaneous and superficial mycoses opportunisitic infections?
no
what is the most common type of fungal infection? where do they infect? are they invasive pathogens?
cutaneous mycoses caused by dermatophytes, which are all molds, causing ringworm/tinea and infections of skin/nails/hair. they are non-invasive and you don’t have to be immunocompromised to be infected.
what is an example of superficial mycoses?
tinea veriscolor, a fungal infection caused by malassezia furfur, (a dimorphic normal skin flora), where pigmentation changes occur
what kinds of infections can be caused by candida? are they opportunisitic?
cutaneous and mucocutaneous infections. candida can be opportunistic, (causing systemic infection), or not depending on the circumstances.
what fungi cause subcutaneous mycoses? how do they enter the body? are they associated with any particular thing in the environment? what kind of infection do they cause?
sporothrix schenkii, a dimorphic fungus, can enter the body through direct inoculation or a puncture wound. it is associated with rose bushes and mulch and causes subcutaneous ulcers that spread along the lymphatics draining the primary lesion.
what are the 2 subgroups under systemic mycoses? what do both affect? what shapes do they take?
opportunistic and endemic mycoses. systemic infections can be caused by molds, (molds in both environment/humans), dimorphic fungi, (mold in environment/yeast in humans), and yeasts, (yeasts in environment and humans)
what is characteristic of endemic mycoses? what is their morphology? are they opportunistic?
they are endemic in specific regions of the US, they are systemic mycoses that are dimorphic and not opportunistic, but more readily disseminate if the host is immunocompromised.
what is characteristic of opportunistic fungi? what do their infections involve and how fatal are they?
they involve internal organs, cause systemic mycoses which can be rapidly fatal
how does candida change when it becomes invasive?
candida is normal flora as yeast, but when it becomes invasive it does expres hyphae and pseudohyphae
what are some examples of endemic mycoses?
blastomyces dermatitidis, coccidioides immitis, and histoplasma capsulatum
what are some examples of opportunistic mycoses?
aspergillus, candida, cryptococcus neoformans, Mucor/rhizopus/zygomycetes) & pneumocystis jirovecii (pneumonia in HIV pts)
what morphology do dimorphic fungi have? how are they transmitted to the pt? what severity are the infections? what is the exposure rate to people in endemic areas? how do they affect immonocompromised patients?
endemic fungi are dimorphic, they are inhaled in mold form and replicate as yeast in tissue. many cases are mild or asymptomatic. most people in endemic areas are skin test positive and immunocompromised patients are prone to disseminated disease.
what area is histoplasma mycoses found in? coccioides?
histoplasma mycoses is found in the mississippi river valley and east. coccioides is found in mexico, particularly desert areas.
who do opportunistic fungi cause systemic infections in?
compromised hosts, such as HIV+, transplant recipients, cancer+leukemia pts, diabetics,(metabolic acidosis – reduced pH, favor fungal growth), pts on long term antibiotics, catheterized pts, (candida, malassezia furfur), burn pts, (candida), individuals with chronic bronchitis/asthma, (aspergillus), and pts recieving corticosteroid tx
what does diganosis of a fungal infection depend on? how is it confirmed?
clinical symptoms and detection of fungus in clinical specimen. this should be confirmed by cx, but pathogens are often slow growing, (days-weeks), and need some type of conidia and/or hyphae are produced, (lactopherol cotton blue is a common stain)
what is a common stain used? why?
potassium hydroxide, (KOH prep), b/c its alkali treament doesn’t destroy chitin+complex polysaccharides. this degrades other eukaryotic cells, allowing the fungi to stand out.
what flourescent stain is used to see fungi sometimes?
calcofluor white, which can be combined with KOH
what is gomori’s methenamine silver?
a popular stain that turns fungi turns black/brown, easier to see
how do fungi appear with gram stains? what does PAS stand for? what are some other general histological stains?
fungi usually appear gram +. PAS stands for periodic acid-schiff, and other general histological stains include giemsa, hematoxylin and cosin
how useful is serology in diagnosing fungal infections? what are they more used for?
serology or (antibody detection), not as useful as with bacteria but can be used to monitor disease progress
what do IgM antibodies indicate in fungal infections? 4xIgG?
IgM indicates acute infection, while 4-fold increase in IgG indicates recent infection
is there antibody dectection available for endemic mycoses? what is a caveat with this process? are there ELISA setups for fungi?
yes, antibody detection of histoplasmosis, blastomycosis and coccidioidomycosis are currently available, (though you may get cross-reactivitiy between fungal antigens). there may be some ELISA setups for these types
are skin tests used to diagnosis?
skin tests are not diagnostic, but they can be used to indicate past or present infection, (fungal antigens may induce cross reactivity with other fungi).
what is the latex agglutination test used for?
very useful for ruling out cryptococcal meningitis (more sensitive than india ink)
what tests can detect aspergillus galactomannan & candida mannan?
ELISA and latex agglutination test which detects surface membrane sugars
what test can be used to look for candida?
tests for D-arabinitol in serum, which is associated w/disseminated candidiasis
what would tests for D-mannitol in bronchoalveolar lavage fluid specimens detect?
pulmonary aspergillosis
what does the limulus lysate assay for beta-1,3-glucan tell you?
if positive, indicates presence of fungus, but doesn’t ID genera. it is useful for patients with invasive candidiasis and aspergillosis
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