Mycology

Terms	Definitions
Penicillium marneffei infections	Cryptococcus is present in 5% of cases of which mould infection?
Cycloheximide and chloramphenicol	What reagents can be added to a fungal culture to selectively inhibit bacterial growth?
Inhalation	Most frequent route of acquiring Histoplasma capsulatum infection?
Calcofluor white	Which fungal stain binds to cellulose and chitin present in fungal cell walls, causing fluorescence under ultraviolet light?
Equal parts of India ink and CSF should be combined.	Interpretation of India ink preparations can be hindered if too much India ink is added, blocking the transmission of light. What is the correct ratio of India ink:CSF that should be placed on a slide?
Cryptococcus neoformans	An organism that demonstrates budding yeast cells with wide capsules in an India ink preparation of spinal fluid is probably _____.
Latex bead antigen agglutination test of the CSF. It's more sensitive and specific than is India ink staining.	India is not done any more to identify Cryptococcus neoformans in the CSF. What test is done.
Candida albicans	The formation of germ tubes presumptively identifies _____.
Cryptococcus neoformans	A budding, encapsulated yeast is found in the CSF of an immunocompromised patient. What is the most likely organism?
Cryptococcus neoformans is the only yeast that produces brown colonies (due to melanin production) on birdseed agar.	Birdseed agar (Staib medium) is useful in identification of which fungal pathogen?
Cryptococcus neoformans	Which is the only pathogenic yeast that is phenol oxidase positive.
Carbohydrate fermentation assay (aka, carbohydrate assimilation assay)	If a CSF yeast non reactive with the cryptococcal latex agglutination assay and does not grow germ tubes, what is the next step in identification of the yeast?
Cycloheximide	Which reagent that is often used to decontaminate specimens for fungal culture can unwittingly inhibit the growth of Cryptococcus neoformans?
Malassezia furfur	Which fungal organism causes catheter-related sepsis, requires lipids from olive oil for growth, and is a small yeast with a wide bud?
Chromogenic agar is extremely effective in detecting mixed yeast populations in clinical specimens.	Two blood cultures are positive for yeast from a patient with an intravenous catheter. One culture grew Candida albicans, while the other grew Candida krusei. Which medium should the technologist use to subculture the blood bottles to in order to verify that the cultures are pure?
35 to 37°C	Chromogenic produces the best color development when incubated at _____.
Candida albicans produce tubular structures with no constrictions (germ tubes) when incubated in rabbit plasma.	This yeast is grown in rabbit plasma.
Candida tropicalis	What organism can be used as a negative control for the germ tube test?
Culture conversion to yeast phase must be performed for identification of dimorphic molds.	Several monomorphic molds resemble the filamentous phase of dimorphic molds. So, what laboratory procedure must be performed in order to confirm that an isolate is indeed a dimorph?
Coccidioides immitis	The arthroconidia of _____ are highly infectious; cultures must be handled with care to minimize aerosols.
Coccidioides immitis	Alternating barrel shaped arthrospores.
Mycelial phase of Histoplasma capsulatum	8-14 µm tuberculate macroconidia
Mycelial phase of Histoplasma capsulatum	8-14 µm tuberculate macroconidia
Histoplasma capsulatum in macrophage
Mycelial phase of Histoplasma capsulatum	8-14 µm tuberculate macroconidia
Sporothrix schenckii	A mold grown at 25°C exhibited delicate septate hyaline hyphae and many conidiophores extending at right angles from the hyphae. Oval, 2-5 µm conidia were formed at the end of the conidiophores giving a flower-like appearance. In some areas "sleeves" of spores could be found along the hyphae as well. A 37°C culture of this organism produced small, cigar-shaped yeast cells. This organism is most likely:
Mycelial growth phase of Sporothrix schenckii
Yes, it is indeed a dimorph	Is Sporothrix schenckii a dimorphic fungus?
Mycelial growth phase of Sporothrix schenckii
Sporothrix schenckii. Appropriately enough, this proximal migration along the lymphatic system is known as sporotrichotic spread.	What dimorphic fungus can cause this clinical presentation?
Conversion of thermally dimorphic fungi in culture requires the use of moist, enriched (blood-containing) agar incubated at 35°C.	How is a thermally dimorphic fungus converted from the mould form (often seen at 25°C) to the yeast form? This is a required procedure before reporting a diagnosis of a dimorph.
Round or pear-shaped small conidia attached to conidiophores of irregular lengths. The microscopic morphology of the mycelial phase of Blastomyces is round or pear-shaped small conidia attached to conidiophores of irregular lengths.	Skin scrapings obtained from the edge of a crusty wrist lesion were found to contain thick-walled, spherical yeast cells (8-15 µm in diameter) that had single buds with a wide base of attachment. Microscopic examination of the room temperature isolate from this specimen would probably reveal the presence of:
Blastomyces dermatitidis	Round or pear-shaped small conidia attached to conidiophores of irregular lengths
Nucleic acid probe test specific for Coccidioides immitis can be completed in <4 hours.	This is isolated from fungal culture of a bronchial wash. What is the most rapid way to definitively identify this organism.
Penicillium marneffei	_____ is a dimorphic fungi that produces a diffusible red pigment.
Microsporum audouinii	Which dermatophytic fungus doesn't have macroconidia or microconidia?
Smooth walled, club-shaped macroconidia	Epidermophyton floccosum macroconidia
Epidermophyton floccosum	Smooth walled, club-shaped macroconidia
Microsporum audouinii	Culture of a strand of hair, that fluoresced yellow-green when examined with a Wood lamp, produced a slow-growing, flat gray colony with a salmon-pink reverse
Microsporum	Hair that fluoresces yellow-green under a Woods lamp indicates the presence of a _____ species.
Microsporum audouinii	Racket hyphae, pectinate bodies (pictured), chlamydospores, and a few abortive or bizarre-shaped macroconidia.
Microsporum audouinii	Racket hyphae, pectinate bodies, chlamydospores (pictured), and a few abortive or bizarre-shaped macroconidia.
Zygomycetes	_____ grow rapidly and fill the dish with cotton candy-like growth (lid lifters).
Microscopic morphology (arrangement of the conidia on the conidiophore)	Penicillium can best be separated from Aspergillus by
Paecilomyces (on the left)	A fungus superficially resembles Penicillium species (on the right) but may be differentiated because the phialides are long and tapering and bend away from the central axis. The most probable identification is
Fusarium	Sickle-shaped macroconidia
Corneal infections	Most common human disease associated with Fusarium spp.
Pseudallescheria boydii	What is the most common organism causing eumycotic mycetoma in the US? Hint: it's not Aspergillus fumigatus
Pseudallescheria boydii	moderately large hyaline septate hyphae with long or short conidiophores, each with a single pear-shaped conidium, 5-7 x 8-10 µm
Pseudallescheria boydii	moderately large hyaline septate hyphae with long or short conidiophores, each with a single pear-shaped conidium, 5-7 x 8-10 µm
Fonsecaea pedrosoi	The only pathogenic mould that produces cladiosporium, phialophora and fonsecaea types of sporulation simultaneously. NB: I have no idea what these three words mean, bu they sounded really cool, so I copied the question. Heck, I don't even know what the picture is of, really.
Indeed, not a parasite, but a fungus	Cryptococcus neoformans once to make it clear, once and for all. It is a fungus (a yeast) and not a parasite!
Very poor with high fatality rate	Prognosis of invasive aspergillosis
The yeast form is favored as the parasitic phase in most dimorphic fungi	Most fungi that can cause systemic infections are dimorphic. Do they tend to be in the yeast phase or the mould phase at body temperature, ie, when acting as a pathogen?
Coccidioides immitis, Paracoccidioides brasiliensis, Blastomyces dermatitidis, Histoplasma capsulatum, Penicillium marneffei, Sporothrix schenckii, Cryptococcus neoformans	A list of clinical important dimorphic fungi (a total of 7 that I cared about)
Meningitis. The nature of neurotropism of C. neoformans is an active research topic and remains an open question.	Most common disease associated with Cryptococcus meningitidis
Spores or desiccated yeast cells of this fungus enter the host respiratory tract by inhalation. Lies dormant in the lungs in granulomas until immune suppression allows reactivation.	How is Cryptococcus meningitidis infection acquired?
The engulfed Candida yeast cells produce hyphae, which kill the macrophage and allow the fungus to continue to grow (pictured).	After a Candida yeast is et by a macrophage, it manages to kill the macrophage and keep growing. How does this microbe do this dastardly deed?
Exophiala werneckii on Sabouraud's dextrose agar	Fungus culture from a pulmonary mycetoma. Initially colonies are mucoid, yeast-like and shiny black, however, with age they develop abundant aerial mycelia and become dark olivaceous in color.
Exophiala spp	Conidia are formed on lateral pegs either arising apically or laterally at right or acute angles from essentially undifferentiated hyphae, or they develop from strongly inflated detached conidia.
Histoplasma capsulatum	PAS-D stain on a lung biopsy. What are the little red spheres?
Histoplasma capsulatum	Silver stain. Granuloma in a lung biopsy. What is the organism?
Histoplasma capsulatum	Ohio and Mississippi river valleys
Histoplasma capsulatum	Macrophage full of organisms that appear to have a capsule. It's not a capsule, but shrinkage artifact. However, that bit of knowledge only came about after the organism already got its name.
Histoplasma capsulatum	Tuberculate macroconidia on culture
Otomycosis (also known as Singapore ear)	A superficial mycotic infection of the outer ear canal that is more common in the tropical countries.
Aspergillus niger and Candida albicans	Most common cause of otomycosis
Clinical presentation of otomycosis	The infection may be either subacute or acute and is characterized by malodorous discharge, inflammation, pruritus, scaling, and severe discomfort. The most characteristic finding on ear examination is the presence of grayish white thick debris known as "wet blotting paper."
Aspergillus niger	Fungal colony from an ear infection.
Aspergillus niger	Hyphae are septate and hyaline. Conidial heads are radiate initially, splitting into columns at maturity.
Aspergillus niger	Hyphae are septate and hyaline. Conidial heads are radiate initially, splitting into columns at maturity.
Aspergillus niger	The phialides arise circumferentially and that black conidia obscure the vesicle
Aspergillus flavus	The phialides arise circumferentially from the globose vesicle
Aspergillus fumigatus	The phialides and conidia extend from the top half of the vesicle.
Aspergillus fumigatus	Unlike most Aspergillus species, _____ grows at 45°C
Aspergillus nidulus	Biseriate conidiogenesis may be difficult to appreciate; metulae are indicated here by the arrowhead, phialides by the arrow.
Aspergillus clavatus	Note the club-shaped vesicle
Histoplasma capsulatum	Spleen FNA from a 35-year-old man with HIV from Mississippi
Penicillium marneffei	Opportunistic dimorphic fungus seen in disseminated infections in AIDS patients from South East Asia.
Tests needed to adequately rule out Penicillium marneffei infection	Tests that should be ordered: culture and stain for both organisms and cryptococcal antigen testing on CSF. Since diagnosis is difficult to make, also get lymph node bx (for LAD) and bone marrow bx for culture and histology.
Penicillium marneffei	Coinfection with Cryptococcus neoformans is seen in 5% of AIDS patients with disseminated _____ infection.
- Candida krusei - C. glabrata has significantly reduced susceptibility to azoles, though it is not intrinsically resistant.	Candida naturally resistant to azoles?
trimethoprim and sulfamethoxazole (TMP-SMX; Bactrim, Septra)	Treatment for Pneumocystis pneumonia (PCP)
Not acquired via inhalation but via skin puncture	Sporothrix schenckii is unique among the endemic, dimorphic fungi in its mode of transmission.
Histoplasma capsulatum, Blastomyces dermatitidis, Coccidioides immitis, Sporothrix schenckii, Paracoccidioides brasiliensis, Penicillium marneffei	Name the six major dimorphic mycoses.
H. capsulatum var. duboisii	Which subspecies of Histoplasma capsulatum is acquired by travel to Africa (not travel to the Ohio River valley)?
An oropharyngeal ulcer, which may cause hoarseness, dysphagia, or a painful lesion on the tongue or gingiva	What is the clinical hallmark of disseminated histoplasmosis?
Macrophages	In which immune cell does Histoplasma primarily reside?
Histoplasma capsulatum	Pathologic lesions consist of collections of infected macrophages, non-caseating granulomas, or caseating granulomas. Histopathologic lesions are similar to those produced by Mycobacterium tuberculosis.
Histoplasmosis	The presence of intracellular small, round to oval yeast-like cells in macrophages is a characteristic pathologic finding.
Histoplasma capsulatum	Diagnostic asexual forms include microconidia and macroconidia. Microconidia, which are produced first, are similar to the structures produced by B. dermatitidis. The more characteristic macroconidia have roughened projections from the periphery of the conidia, a configuration referred to as tuberculate.
Blastomyces dermatitidis	Tissue section showing large, broad-base, unipolar budding yeast-like cells.
Blastomyces dermatitidis	The lollipop appearance of the conidium on a conidiophore is characteristic of this dimorphic fungus. Lick my lolly.
Coccidioides immitis	What is the California clade of Coccidioides?
Coccidioides posadasii	What is the non-California clade of Coccidioides?
None	What is the morphologic difference between Coccidioides immitis and C. posadasii?
Coccidioides	The tissue response to this dimorphic fungus is granulomatous, with and without caseation. Developing spherules are typically found in macrophages and multinucleated giant cell.
Coccidioides spp.	Alternating barrel-shaped arthroconidia
Found in the soil in a world-wide distribution	Endemic area of Sporothrix spp.
Alcohol consumption (the alcoholic rose gardener)	What is the only know risk factor for sporotrichosis?
Cutaneous sporotrichosis	Splendore-Hoeppli phenomenon (asteroid bodies)
Sporothrix spp.	This organism produces two types of conidia: thin-walled hyaline conidia arranged as a rosette around the apex of a conidiophore, and thick-walled, dark, sessile conidia attached directly to the hyphae. The thin-walled microconidia are borne on conidiophores that arise at right angles from the hyphae.
Paracoccidioides brasiliensis	Mariner's wheel yeast cells
Penicillium marneffei	The only Penicillium spp. to be dimorphic
Aspergillus flavus	Which species of Aspergillus has fluffy colonies due to fruiting bodies and yellow or green coloration within white colonies?
Aspergillus flavus	Conidiophores are at the tips of the conidia (not surrounding the tip of the conidia).
Aspergillus nidulans	Which Aspergillus species is inherently resistent to amphotericin B?