mycology Flashcards
mycology
most are free-living and abundant in nature; only a few are members of the human microbiome; fungi are eukaryotic microorganisms
fungi
cell walls made of chitin; chitin provides a very tough cell wall; the biosynthesis of chitin provides a target for antifungal agents; fungal plasma membranes contain egosterol, which is a cholesterol analog not found in plant or animal cells; ergosterol provides a target for antifungal agents
filamentous fungi
form branching tufts called mycelium; filamentous fungi grow by extending cells called hyphae; as fungal hyphae expand, its chitinous cell wall enables it to penetrate softer material, such as plant or animal cells; they can expand a great length, but eventually they run out of nutrients; the gametes develop into spores (conidia) that are easily airborne and disseminate into the environment; fungal spores can spread disease and cause allergies; the vast majority of fungi do not need to colonize or infect humans or animals to perpetuate the species
single-celled fungi
unicellular fungi are called yeasts; most yeasts reproduce by mitosis through asymmetric division process known as budding
dimorphic fungi
some species of fungi are dimorphic; they can exist in a mycelial or yeast form depending on the growth environment
pathogenic fungi
nearly all fungal infections originate from an exogenous source either by inhalation or traumatic implantation; the exceptions are candidiasis and tinea versicolor, which are caused by opportunistic microbiota;
saprobes
organisms that live on dead or decaying organic matter
tinea versicolor
(superficail mycoses) - part of the nromal microbiota of the skin; hyper- or hypo-pogemented macular lesions on the upper torso, arms, and abdomen
tinea nigra
(superficial mycoses) - fungi that produces melanin giving it a brown to black color; causes well-demarcated macular lesions mostly on the palms an soles
black piedra
(superficial mycoses) - infects the hair shaft; causes hard nodules to form along the infected hair shaft
white piedra
(superficial mycoses) - infects the hair shafts of the scalp, mustache or beard; forms a soft, pasty, cream-colored growth along the infected hair shaft
ringworm
(cutaneous mycoses) - caused by a closely related group of fungi known as dermatophytes; the fungi that cause ringworm can live on skin and in the environment; ringworm is spread: through contact with a person or animal who has ringworm; from the environemnt: the fungi can live on surfaces, particularly in damp areas like locker rooms and public showers
subcutaneous mycoses
subcutaneous mycoses comprise a wide spectrum of fungal infections characterized by the development of lesions usually at sites of trauma where the organism is implanted in the tissue; the infection initially involves the deeper layers of the dermis, subcutaenous tissue or bone
histoplasmosis
systemic mycoses - histoplasmosis is acquired from inhaling the spores or hyphal frangments of histoplasma capsulatum; once inhaled, H. capsulatum phagocytosed by pulmonary macrophages. the fungi then convet into the yeast form, which are able to replicate within the macrophages.
h. capsulatum
grows in soil; especially in areas containing bird and bat excretions
histoplasmosis symptoms
in most cases it is asymptomatic, but in about 5% of cases acute pneumonia develops and less often 1% is followed by progressive disseminated disease; this level of disease occurs in debilitated and/or immunosuppressed individuals
blastomycosis
most infections are asymptomatic; the symptoms of blastomycosis are often similar to the symptoms of flu or other lung infecitons; in some people, particularly those with weakened immune systems, the fungi can spread to other parts of the body
cryptococcosis
acquired from inhaling cryptococcus neoformans; encapsulated yeast; once inhaled, C. neoformans may infect the lungs; however, the organism has a high tendency for systemic spread to the brain and meninges; leading cause of fungal meningitis
where is c. neoformans found
it lives in the environment throughout the world; the fungus is generally found in soil, on decaying wood and in bird (pigeon) droppings
cytococcosis infections
extremely rare among people who have healthy immune systems; however, C. neoformans is a major cause of illness in people living with HIV/AIDS; a c. neoformans infection in the lungs can cause a pneumonia-like illness; cryptococcal meningitis occurs if the fungus spreads from the lungs to the brain; the symptoms of cryptococcal meningitis are similar to other forms of meningitis
candidiasis
opportunistic mycoses - caused by a species of Candida, many of which are members of the human microbiome; candida species are monomorphic yeasts and can be found in the human oral cavity, vagina, gastrointestinal tract, and rectum; within the human host, candida species’ growth is limited by competition with other microbiota and the immune system; disease results when the fungus overgrows and offsets the balance
oropharyngeal candidiasis
opportunistic mycoses - candidiasis that develops in the mouth or throat is called “thrush” or or oropharyngeal candidiasis; characterized by white patches or plaques on the tongue and other oral mucous membranes, redness and difficulty swallowing; oral thrush occurs most frequently among babies less than one month old, the elderly and groups of people with weakened immune systems
genital candidiasis
opportunistic mycoses - genital/vulvovaginal candidasis is also sometimes called a “yeast infection,” and it occurs when there is overgrowth of normal yeast in the vagina; men with genital candidiasis may experience an itchy rash on the penis
invasive candidiasis
opportunistic mycoses - if candida get into the bloodstream (candidemia), it can affect the blood, heart, brain, eyes, bones or other parts of the body; the most common symptoms are fever and chills that don’t improve after antibiotic treatment for suspected bacterial infections
