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
aspergillosis
caused by aspergillus, which are extremely common in the environment both indoors and outdoors; aspergillosis is acquired from inhaling spores from exogenous sources; most people do not get sick, however it is an opportunistic pathogen for people with weakened immune systems or lung diseases
allergic aspergillosis
a benign allergy involving the lungs and/or sinuses
aspergilloma
also called a “fungus” ball’ a ball of aspergillus grows in the lungs or sinuses but usually does not spread to other parts of the body
chronic pulmonary aspergillosis
a long-term condition in which Aspergillus can cause cavities in the lungs; one or more fungal balls (aspergillomas) may also be present in the lungs
systemic aspergillosis
in immunosuppressed hosts the organism spreads from its primary site (lungs) to other tissues causing infarcts and hemorrhage
