Clinical Study Questions (Mycology and Parasitology) Flashcards
What are arthrospores?
result from simple fragmentation of the hyphae into square or rectangular spores
What are blastospores?
simple budding - daughter cell forms and separates from the mother cell
What would you call a daughter cell that elongates and does not detach from the mother cell?
pseudohyphae
What are chlamydospores?
thick-walled, resistant cells that form when hyphae round up and enlarge; they can be located at the tips of the hyphae (terminal), on the sides of the hyphae (sessile), or within the hyphae (intercalated)
What is a germ tube and how is it interpreted?
short, lateral hyphae filaments on individual yeast cells, particularly those belonging to the Candida genus; observation of germ tubes in a yeast wet prep is positive, and can indicate C. albicans or C. stellatoidea
What is lactophenol cotton blue (LPCB) and how is it used in mycology?
mounting medium for examining a fungal culture that has already sporulated; designed to preserve fungal structures (lactic acid), reduce contamination of the environment (phenol), and stain the fungal hyaline structures (cotton blue)
How is a KOH mount used in mycological studies?
used on specimens obtained directly from the body; employs 10-20% KOH, which clears away keratinous material, allowing hyaline fungal elements to be easily seen
How is the India ink preparation performed and for what organism is it most useful?
performed on CSF to look for Crytptococcus neoformans; a drop of specimen is mixed with a drop of India ink on a glass slide and coverslipped - capsule will be visible as a clear halo around the organism
What is the morphology of C. albicans?
yeast producing blastospores, chlamydospores, germ tubes, and pseudohyphae (no true hyphae); non-pigmented, medium-sized, creamy white colonies
What laboratory tests can be done to confirm an identification of C. albicans?
performing a wet prep to confirm the presence of yeast; perform a germ tube test (+ presumptive for C. albicans); confirm with chlamydospore production on cornmeal/chlamydospore agar; and/or perform sucrose assimilation (+) and fermentation (=) tests
How can C. albicans be differentiated from Geotrichum?
Geotrichum is a fungus, and therefore has true hyphae; it also produces arthrospores but not blastospores, while C. albicans produces the opposite.
What is thrush?
Oral C. albicans infection, seen most often in infants and older people (especially if they are debilitated). Grows on the tongue at the back of the mouth in creamy white patches; not usually serious, though if left untreated it can form a pseudomembrane over the tonsils and block the airway.
How would a skin specimen be collected for a KOH prep?
clean skin with 70% alcohol to eliminate normal flora; use a clean (flamed) slide or sterile Bard-Parker blade to scrape the outer area of the lesion - material should be placed in a sterile Petri dish or pressed between two slides until the KOH prep is done
How would a nail specimen be collected for a KOH prep?
clean nail(s) with 70% alcohol; use a sterile blade to scrape the diseased portion of the nail, preferably obtaining fine shavings of all three nail layers - transport as you would a skin specimen
How would a hair specimen be collected for a KOH prep?
if hair falls out, it should be placed in a sterile Petri dish; if not, tweezers should be used to remove the hair, as the entire shaft is needed (with Trichosporum tonsurans, the hair will break off at the scalp, so it may be necessary for a doctor to work the shaft out with tweezers or a blade)
What are the five species of dimorphic fungi?
Histoplasma capsulatum, Blastomyces dermatitidis, Coccidioides imitis, Paracoccidioides braziliensis, Sporothrix schenckii
What three media are commonly used for the culturing of fungi?
Sabouraud’s with dextrose, Mycosel, and Potato-Dextrose agar
What safety measures should be observed in preparing a slide mount for fungi that have white aerial mycelium?
do NOT make slide mounts with anything other than a slant culture; work under a hood, and make sure to moisten the colony with sterile saline or DI water before gathering a slide specimen to prevent contaminating the environment with spores
What is the (1) macroscopic appearance, (2) microscopic appearance, and (3) mode of transmission for Microsporum audouinii?
(1) forward is velvety-white or cream, may appear fluffy; reverse is mahogany. (2) septate hyphae with (generally terminal) chlamydospores that may be pointed at one end; may see poorly-shaped microconidia or racquet hyphae; may see nubins. (3) infected hairs, combs, upholstery, etc.
What is the (1) macroscopic appearance, (2) microscopic appearance, and (3) mode of transmission for Trichophyton schoenleinii?
(1) cream to grey, glaborous, waxy colony resembling a sponge; irregular border (color ages to yellow/tan). (2) hyphae usually sterile, pinhead/nailhead type; few microconidia; NO macroconidia; favic chandeliers. (3) direct or indirect contact with skin or scalp lesions of infected individuals.
What is the (1) macroscopic appearance, (2) microscopic appearance, and (3) mode of transmission for Cryptococcus neoformans?
(1) cream-colored, smooth, mucoid colonies. (2) oval to spherical, single-budding, thick-walled yeast surrounded by a wide, refractile, gelatinous capsule. (3) close contact with pigeons and/or their droppings.
What is the (1) macroscopic appearance, (2) microscopic appearance, and (3) mode of transmission for Aspergillus fumigatus?
(1) flat, white, and filamentous with a blue-green powdery surface and a colorless reverse. (2) branching, septate hyphae with conidia produced on terminal conidiospores that have a swelling or vesicle with flask-like phialides. (3) inhalation of spores.
What is the (1) macroscopic appearance, (2) microscopic appearance, and (3) mode of transmission for Trichophyton tonsurans?
(1) begins as flat, white, powdery colonies; later becomes grey to sulfur yellow to tan, surface shows radial folds and develops a central depression with deep fissures; reverse is yellowish to reddish brown. (2) septate hyphae with microconidia (tear drop, club, or balloon-shaped), either sessile or from short sterigmata resembling match sticks; macroconidia are irregularly shaped with thin walls and blunt ends (rarely seen); chlamydospores may be seen in older cultures; hyphae tend to stain ireegularly with LPCB; spiral coils, racquet hyphae, and arthrospores may be seen. (3) contact with another infected individual.
What is the (1) macroscopic appearance, (2) microscopic appearance, and (3) mode of transmission for Microsporum gypseum?
(1) flat, spreading, and suede-like; buff, pinkish-tan, or “cinnamon” in color; reverse is tan or pale yellow to orange. (2) many macroconidia with rounded ends, 3-9 cells (usually 6), rough- and thick-walled, somewhat “rowboat” shaped. (3) most often seen in football players and other athletes that have their bodies pushed into the ground (organism is geophilic).
What is the (1) macroscopic appearance, (2) microscopic appearance, and (3) mode of transmission for Epidermophyton floccosum?
(1) velvety, granular, wrinkled, numerous radiating furrows that are distinctively greenish-yellow (yellow-brown with age); reverse varies from white to yellow-brown. (2) club-shaped macroconidia with thin and smooth walls, in sets of 2-5 cells (clustered in 2-3 sets on the hyphae, or can appear singly); no microconidia; chlamydospores present; nodular bodies, racquet hyphae, and spirals can be seen (rare). (3) direct or indirect contact with skin or scalp lesions of an infected individuals.
What is the (1) macroscopic appearance, (2) microscopic appearance, and (3) mode of transmission for Coccidioides immitis?
(1) after 3-5 days, white cottony mycelium; buff to brown color with age. (2) mold phase characterized by barrel-shaped arthrospores; often appear as chains of alternating spores with “empty” cells. (3) inhalation of spores.
What is the (1) macroscopic appearance, (2) microscopic appearance, and (3) mode of transmission for Histoplasma capsulatum?
(1) starts out white, wooly/fluffy; may become dry, tan, and wrinkled with age; reverse may turn brown. (2) small, oval, microconidia with smooth walls and large, spiny, tuberculate macroconidia. (3) inhalation of spores from free-living fungus found in the soil.
What is the (1) macroscopic appearance, (2) microscopic appearance, and (3) mode of transmission for Candida albicans?
(1) medium-sized, smooth, pasty, cream-colored colonies. (2) blastospores, pseudohyphae, germ tubes, chlamydospores (when growing on appropriate agar). (3) usually normal flora - opportunistic pathogen.
What are the advantages of the zinc sulfate flotation concentration procedure?
organisms remain alive and motile, and larvae within the eggs remain viable; interfering pigment is washed out along with any debris prior to the addition of the ZnSO4
What are the disadvantages of the zinc sulfate flotation concentration procedure?
time required to complete the procedure; specimens preserved in formalin cannot be used; operulated eggs, infertile Ascaris eggs, and schistosomes will be missed; kills protozoan trophs and distorts fragile eggs
What are the disadvantages of the formalin ether sedimentation concentration procedure?
protozoan trophs do not survive the process
What are the two most common permanent stains used to make protozoan slides?
trichrome, Lawless HgCl2
Why is the iron hemotoxylin permanent stain not commonly used in clinical labs?
procedure takes 3 days to complete
Define PVA.
polyvinyl alcohol; fixative for stool specimens
Define flagellates.
any of a group of protozoans, mostly uninucleate organisms, that possess, at some point, one to many flagella for locomotion and sensation
Define MIF.
Merthiolate-Iodine-Formalin; stool collexion and preservation kit - iodine stains trophs immediately, and cysts in a short period; formalin preserves helminth ova and protozoa (allows patients to collect specimens at home and bring to the lab for testing)
Define Chaga’s disease.
caused by the protozoan parasite Trypanosoma cruzi; endemic to Latin America, transmitted through contact with the contaminated feces of triatomine (“kissing”) bugs
Define sporogeny.
sexual stage in the life cycle of a sporozoan protozoa, with development of the zygote into one or several haploid spores, each containing a distinct number of sporozoites
Define definitive host.
also called “final host”; the organism in which the parasite passes its adult existence and/or its sexual reproductive stage
Define symbiosis.
permanent association of two organisms of different species that cannot exist independently
Define intermediate host.
the organism in which the parasite passes part or all of its larval and/or its asexual reproductive stage
Define microfilariae.
the prelarval form of any filarial worm; certain blood-sucking insects ingest these from infected hosts, and the microfilariae develop inside the insect body, becoming infective larva
Define periodicity.
events or episodes that tend to repeat at predictable intervals
Define cysticercus.
larval form of certain Taenia species, typically found in the muscles of mammalian intermediate hosts that serve as prey for various predators; consists of a fluid-filled bladder in which the invaginated cestode scolex develops
Define hydatid sand.
the scoleces, daughter cysts, hooks, and calcareous corpuscles of Echinococcus tapeworms in the fluid of a primary or daughter hydatid cyst
Define scolex.
the attachment organ (mouth) of a tapeworm, generally considered the anterior (cephalic) end
Define miracidium.
the ciliated first-stage larva of a trematode that emerges from the egg and must penetrate into an intermediate host snail to continue its life cycle
Define cercariae.
final, free-swimming larval stage of a trematode parasite; develops in the sporocyst
Define sporocyst.
germinal, sac-like stage of digenetic trematodes, produced by metamorphosis of a miracidium and giving rise to rediae; stage in the life cycle of certain coccidian protozoa, contained within the oocyst, produced by a sporoblast, and giving rise to sporozoites
Define exflagellation.
the protrusion or formation of flagelliform microgametes from a microgametocyte in malarial parasites and some related sporozoa
Define leishmanial form.
form that Leishmania parasites take in their vertebrate host, where they do not have any visible external flagella or cilia
Define operculated egg.
egg that has a lid or caplike cover, usually seen in certain trematode and cestode parasite species
Define merozoite.
motile, infectious stage of sporozoan protozoa that results from schizogeny or a similar type of asexual production
Define schizont.
stage in the development of the malarial parasite following the trophozoite, whose nucleus divides into many smaller nuclei
Define trophozoite.
an elongated cell that develops from a sporozoite or merozoite of an apicomplexan parasite, and that feeds and grows in the host
Define rhabditiform larvae.
early developmental larval stages (1st and 2nd) of soil-borne nematodes such as Necator, Ancylostoma, and Strongyloides
Define proglottid.
one of the segments of a tapeworm, containing both male and female reproductive organs
Define filariform larvae.
infective third stage larva of the hookworm Ascaris, and other nematodes with penetrating larvae or larvae that migrate through the body to reach the intestine
Why is an asymptomatic infection of Strongyloides so dangerous to an immunosuppressed host?
immunosuppressed hosts are at risk of disseminated infection, and being asymptomatic increases the odds that the parasite goes undetected until the infection is too far gone
Why would a blood transfusion from a donor who has great numbers of microfilariae not be dangerous to the recipient?
microfilariae are not the infective stage of development; they require an insect vector in which they can continue their life cycle in order to do any harm
Why is a stool contaminated with barium not suitable for ova and parasite studies?
barium obscures the identification of ova and parasites
In what types of parasitic infection is a duodenal aspirate the specimen of choice?
when infection due to Clonorchis, Giardia, or Strongyloides is suspected
How would chronic amoebiasis be diagnosed?
look for the presence of ova in the stool - black tar-like stools can indicate an intestinal bleed due to overgrowth causing an abscess; amoebic hepatitis (abscesses in the liver) indicates long-term infection; presence of eosiniphils (eosinophilia) and Charcot-Leyden crystals
What are the names for malarial pigment?
hemazoin, hematin, or hematozoin
What are the two methods for toxoplasmosis diagnosis?
(1) demonstrate a rise in IgM or IgG antibodies through indirect fluorescent assay or indirect hemagglutination. (2) Sabin-Feldman dye test - in the presence of antibody, Toxoplasma will NOT stain with methylene blue
What is the common name for Taenia saginata and what are its characteristics?
beef tapeworm (intermediate host is cattle); scolex has 4 suckers that do NOT have a rostellum or hooks; proglottids are longer than they are wide, with lateral genital pores instead of a central uterine pore; uterus has 15-30 branches on each side
What is the common name for Taenia solium and what are its characteristics?
pork tapeworm (intermediate host is the pig); scolex has 4 suckers WITH a fleshy rostellum and a double row of well-defined hooks; proglottids are more square, and the uterus has only 7-15 lateral branches
Why is a T. solium infection far more dangerous than a T. saginata infection?
T. saginata infection is usually asymptomatic; any symptoms are usually mild, and the infection in not life-threatening. However, ingesting T. solium ova can result in a condition called cysticercosis - when the ova are ingested, they lose their outer covering and invade the bloodstream and tissue (brain infections are common). While some patients may remain asymptomatic, death can occur in other, more extreme, cases.
Which stool specimens should be processed for parasites without delay?
liquid stools; this is where trophs are most likely to be seen, and they will begin to lyse once the stool cools (30-45 minutes)
What should be done with a stool specimen if it cannot be processed immediately?
Technologist should perform a macroscopic exam, looking for any mucus or blood (where organisms are most likely to be). These areas should be targeted for sampling and then preserved until the microscopic exam can be performed. 10% formalin would probably be the best method of preservation as it will keep any organisms in as near a natural state as possible, as well as preserve any eggs, cysts, or larvae.
Which malarial parasite is associated with periodic fevers every fourth day (quartian malaria) and is characterized by the “daisy-head” or “segmenter” formation?
Plasmodium malariae
What is the most common infectious disease in the world?
Mycobacterium tuberculosis
What specimen would be recommended to diagnose Blackwater Fever?
blood, urine
What specimen would be recommended to diagnose trichinosis?
blood, muscle biopsy
What specimen would be recommended to diagnose whipworm infection?
stool
What specimen would be recommended to diagnose large roundworm?
blood, stool
What specimen would be recommended to diagnose seatworm?
stool, Scotch tape prep
What specimen would be recommended to diagnose elephantiasis?
blood sample collected at night
What specimen would be recommended to diagnose onchocercosis?
skin or nodule biopsy, examining the eyes with a slit-lamp
What specimen would be recommended to diagnose visceral larval migrans?
blood
What specimen would be recommended to diagnose fish tapeworm?
blood, stool
What specimen would be recommended to diagnose amoebic hepatitis?
blood, stool
What specimen would be recommended to diagnose Giardiasis?
stool, duodenal aspirate
What specimen would be recommended to diagnose African sleeping sickness?
blood (T. b. rhodesiense), lymph node aspirate (T. b. gambiense)
How can Entamoeba histolytica be differentiated from Entamoeba coli?
(1) E. histolytica exhibits progressive, directional movement; the nucleus has evenly distributed peripheral chromatin and a small central karyosome. (2) E. coli is blob-like, with very little ectoplasm; moves very sluggishly; uninucleate, uneven peripheral chromatin and an eccentric karyosome; also may have one or more pseudopods.
What parasite causes visceral leishmaniasis?
Leishmania donovani
What is the morphological form of Leishmania donovani?
intracellular L-D bodies
