Mycology

Mucormycetes (formerly known as the Zygomycetes) grow extremely rapid both in vivo and in culture. They are often called

"lid lifters" because of their fluffy and voluminous aerial mycelia that can lift the lid off of plates whose lids aren't taped on. Their hyphae are broad and have few septae, making them floppy and ribbonlike. Their branching is infrequent, haphazard and nondichotomoous. Extreme care must be taken not to grind specimens prior to culture if zygomycosis is a consideration as the grinding process can disrupt all of the viable hyphae. Instead, tissue specimens should be minced.

Coccidioides spp. grows moderately to rapidly in its mold form whether incubated at

25-30ºC or 37ºC and initially forms glabrous, moist, gray colonies that become white and cottony when mature.

The typical hyphae of the Aspergillus spp. are

3 to 6 µm in width, septate, and dichotomously branched at 45 degree angles.

Hilar cells of Microsporum canis appear fractured where it was released from the stolon. Macroconidia having this so-called "break-away" cell are termed: Ascospsores Dictyospores Aleureospores Arthrospores

Aleureospores

Most common clinical manifestations of cryptococci

Although infection most often occurs by inhalation of cryptococci, diseases of the central nervous system such as meningoencephalitis are the most common clinical manifestations

The differentiation between Aspergillus species and Scedosporium species may be difficult when only hyphal elements are observed in stained tissue sections. It is important to obtain a culture to make this differentiation when possible because Scedosporium species, in contrast to Aspergillus species, tend to be resistant to:

Amphotericin B *administration of one of the imidiazoles is recommended

Aspergillus species that would be the most likely species witht he potential for producing cleistothecia: fumigatus niger nidulans flavus

Aspergillus nidulans

The multi-celled conidia of this dematiaceous mold are divided into cells by what are called distosepta (pseudosepta), indicating that the individual cells are surrounded by a sac-like wall that is distinct from the outer cell wall of the conidium. The identification of this mold is: Curvularia species Exserohilum species Stemphilium species Bipolaris species

Bipolaris *the thickened, sac-like structures surrounding the central, spherical cells. These are in contrast to the distinct septa derived from the cell wall as seen with Curvularia species.

Dematiaceous molds growth Bipolaris, Curvularia, and Alternaria spp. Scedosporium apiospermum/boydii Scedosporium prolificans

Bipolaris, Curvularia, and Alternaria spp. grow relatively rapidly. Scedosporium apiospermum/boydii is a moderately rapid grower. Scedosporium prolificans is slow growing.

Two Cryptococcus spp that cause cryptococcosis

C. neoformans C. gattii

Most commonly encountered human yeast pathogen

Candida albicans

Difference b/w C. glabrata and other Candida spp

Candida species other than C. glabrata are generally moderately sized yeasts, ranging in size from 5 - 7 µm that may produce pseudohyphae and/or hyaline septate hyphae, depending on the species. Deep infections can produce true hyphae, but the detection of budding yeast help aid in the diagnosis of candida. Candida glabrata are smaller, ranging from 2 - 4 µm in diameter, and cannot produce hyphae or pseudohyphae.

Match: Brain Abscess Chromomycosis Subcutaneous Phaeohyphomycotic cyst Chronic sinusitis Cladosporium trichoides Bipolaris Phialophora verrucosum Phialophora richardsiae

Cladosporium trichoides Phialophora verrucosum Phialophora richardsiae Bipolaris

Conidia in clusters/chains: Phialophora verrucosa Alternaria spp Exophiala spp Cladosporium spp

Clusters Chains Clusters Chains

Hyaline molds Conidia in chains or clusters: Aspergillus fumigatus Scopulariopsis species Gliofladium species Acremonium species

Conidia in chains Conidia in chains Conidia in clusters Conidia in clusters

Stains for Cryptococcus

Cryptococcus stains poorly using Haemotoxylin and Eosin (H&E) but is readily highlighted using Periodic acid-Schiff (PAS) and Gomori methenamine silver (GMS) stains. The capsule is most commonly demonstrated using the mucicarmine stain. The Fontana-Masson stain is positive in metabolically active yeasts and may stain the melanin-like components in the yeast cell walls.

Dermatophyte vs. Zygomycete: Microsporum nanum Trichophyton schoenleinii Epidermophyton floccosum Cunninghamella spp

Dermatophyte (first 3) Zygomycete

Match morphological feature: Hilar cell extension Sporodochium Rhinocladiella type sporulation Macroconidia with enlarged center cells Exserohilum spp Fonsecaea pedrosoi Epicoccum spp Curcularia spp

Exserohilum spp Epicoccum spp Fonsecaea pedrosoi Curvularia spp

Dematiaceous fungi producing a black, suede-like colony reaching no larger than the size of a dime after 7 days incubation: Curvularia species Alternaria species Fonsecaea species Nigrospora species

Fonsecaea species

most commonly isolates Fusarium spp.

Fusarium moniliforme, Fusarium oxysporum, and Fusarium solani

Main difference b/w Trichoderma spp and Gliocladium spp

Gliocladium spp are supported by multiple conidiophores while Trichoderma spp are spherical and aggregate in tight clusters supported by a single, tapered phialides that extend laterally from the hyphae

Major mechanism that predisposes patients to cryptococcal disease

Immune suppression associated with AIDS, diabetes, chronic liver disease, chronic renal disease, prolonged use of steroids, and organ transplant

Patients at high risk for infections of Rhodotorula

Immunocompromised patients, especially those with central venous catheters or other indwelling catheters, are at high risk for infections, most commonly presenting as fungemia. Other types of infection include endocarditis, meningitis, peritonitis, and ocular infection. Prophylaxis or treatment with fluconazole has been recognized as a risk factor for fungemia.

The rapid diagnosis of dermatophytosis can be made with a bedside by

KOH or calcofluor white preparation of skin scrapings. Microscopy cannot be used to distinguish among the dermatophytes; only culture can do so.

Yeast resembling bowling pins, while daughter cell budding from the parent cell is sometimes likened to a turtle head coming out of its shell.

Malassezia spp

most common cutaneous infections in the tropics and subtropics worldwide.

Malassezia spp. are commensals of the skin. Some species are lipid-dependent. Tinea versicolor is a common infection of the superficial epidermis caused by Malassezia spp *rarely cause bloodstream infections; these are usually associated with an indwelling intravascular catheter and the administration of hyperalimentation that contains lipids.

The hyaline saprobic fungus that has microscopic features similar to the mold form of Coccidioides immitis is: Malbranchia species Geotrichum species Trichosporon species Microsporum canis

Malbranchia species *Malbranchia species share the production of alternate staining arthroconidia as a common feature with the mold form of Coccidioides immitis.

An infrequently encountered mold that begins as a gray-white colony that blackens with maturity as the hyphae become darkened and single, globose, black conidia are produced: Pseudallescheria boydii Nigrospora species Scopulariopsis brumptii Stemphilium species

Nigrospora species

Usually pathogenic/not pathogenic: Alternaria spp Fonsecaea pedrosi Phialophora verrucosa Bipolaris species

Not Pathogenic Pathogenic Pathogenic Not Pathogenic *Of the fungi listed in this exercise, Fonsecaea pedrosoi and Phialophora verrucosa, each serving as agents of chromomycosis, are generally considered "pathogenic" species. Alternaria species and Bipolaris species are usually not pathogenic, but may cause opportunistic infections in debilitated patients, commonly sinusitis from the inhalation of spore-laden dust; or, subcutaneous mycetomas where spore-infected vegetative material has been traumatically inoculated into the skin.

Which supplement is necessary to add to culture media to ensure proper growth of Malassezia species?

Olive Oil Tween

Opportunistic pathogen vs. Obligate pathogen: Aspergillus fumigatus Rhizopus spp Acremonium spp Blastomyces dermatitidis

Opportunistic pathogen (first 3) Obligate pathogen

Flask shaped conidiogenous cells on lactophenol blue mount. Dull white fungus, turning mouse gray on maturity. Scedosporium apiospermum Scedosporium prolificans (inflatum) Sepedonium species Chrysosporium species

Scedosporium prolificans (inflatum)

The chain of conidia with the deep-staining truncated bases, are called annelloconidia, and are most characteristic of: Cladosporium species Scopulariopsis brumptii Alternaria species Aureobasidium pullulans

Scopulariopsis brumptii

The hyaline saprobic fungus that has microscopic features similar to the mold form of Histoplasma capsulatum is: Chrysosporium species Malbranchia species Sepedonium species Scopulariopsis species

Sepedonium spp

Spores in sporangia or cleistothecia: Syncephalastrum spp Mucor spp Pseudallescheria boydii Aspergillus nidulans

Spores in sporangia Spores in sporangia Spores in cleistothecia Spores in cleistothecia

most commonly isolated of the six Trichosporon spp.

T. asahii, T. inkin, and T. mucoides

All of the species listed below produce microconidia that aggregate in clusters: TRUE/FALSE Trichoderma species Acremonium species Fusarium species Gliocladium species

TRUE

Which are the major factors contributing to the virulence of the Cryptococcus spp

The capsule of the fungus is comprised of the polysaccharides glucuronoxylomannan and glucuronoxylomannogalactan

How do you distinguish C. glabrata from Histoplasma capsulatum (morphologically the same)

The presence of a predominately neutrophilic inflammatory response to C. glabrata is helpful in distinguishing infection with this organism from H. capsulatum; a hallmark of infections with the latter is a granulomatous response, comprised largely of macrophages

The most helpful feature in differentiating the Zygomycetes from the other hyaline molds in the clinical mycology laboratory is: Rapid growth rate The production of spores within sporangia The production of rhizoids The formation of aseptate hyphae

The production of spores within sporangia

Match the names of each of the fungi listed with its appropriate category depending upon whether the multi-celled macroconidia are divided by both longitudinal and transverse septa (dictyospores); or, are divided by only transverse septa. Exserohilum spp Epicoccum spp Curvularia spp Ulocladium spp

Transverse septa Dictyospores Transverse septa Dictyospores

Gliocladium produces a "green lawn" colony with no margin, what is the other hyaline mold that produces this type of colony? Trichoderma spp Paecilomyces spp Aspergillus flavus Rhizopus spp

Trichoderma spp *Although both Paecilomyces species and Aspergillus flavus may produce green colonies, they always have a margin, usually with a distinct white apron at the outer margins of new growth. Rhizopus species also produces a "lawn" like colony that extends from border to border in the Petri dish; however, it never produces a green pigment.

"birds on the fence" arrangement of uniform sized, tear-chaped microconidia is characteristic of: Trichophyton tonsurans Trichophyton mentagrophytes Trichophyton rubrum Trichophyton verrucosum

Trichophyton rubrum

Diagnosis of disseminated histoplasmosis can be made with an antigen test performed on urine or serum. True False

True

Microscopically, S. schenckii mold-forms produce very delicate hyaline septate hyphae producing conidiophores topped by clusters of microconidia ("rosettes"). True False

True

T. rubrum lactophenol cotton blue preparation showing

a large, septate macroconidium, and numbers of smooth-walled, teardrop-shaped microconidia.

Disseminated cryptococcosis infection is defined by

a positive blood culture or a positive culture from at least two different sites. Disseminated infection is commonly associated with HIV infection or several other immunocompromising conditions.

Trichosporon spp. hyphae are often arranged in

a radial pattern

Microscopically, all cultured Aspergillus spp. produce

a swollen vesicle ("aspergillum") at the end of each conidiophore (which is a feature distinct to the genus). Identification to the species level is based on characteristic colony and microscopic morphologies.

S. boydii is intrinsically resistant to

amphotericin B, but is usually susceptible to broad spectrum triazoles such as voriconazole and posaconazole.

The spores of Alternaria spp

are multicellular, pigmented, and are produced in straight or branching chains. The end of the conidium nearest the conidiophore is rounded, and tapers towards its apex, imparting a beak-like appearance.

Dermatophyte: The macroconidia of Microsporum gypseum

are oval-shaped and have rounded ends. Each contains 3 - 6 cells.

Dermatophyte: Microsporum canis macroconidia

are spindle-shaped, rough, and taper to a knoblike end. Each contains >6 cells, separated by transverse septae.

The disease caused by Histoplasma spp., histoplasmosis, may be

asymptomatic and diagnosed incidentally as a "coin lesion" on chest X-ray. It has the potential to cause acute or chronic pulmonary infection. This can occur in workers exposed to a large inoculum in construction or cave excavation. H. duboisii causes the disease African histoplasmosis, which involves skin and bones and rarely the lungs. *The immunocompromised are at risk for disseminated histoplasmosis following pulmonary infection. Disseminated infection may lead to oropharyngeal ulcers, hepatic and/or splenic involvement, or infection of the bone marrow, CNS, major arteries, or cardiac valves.

T. tonsurans culture plate demonstrating

at the center of the colony a wrinkled appearance, though, overall, the colony exhibits a glabrous or smooth velvety appearance, as well as its characteristic yellowish-beige coloration

Cleistothecia

bag like structures containing smaller structures call asci w/in which ascospores are produced

Arthroconidia of Coccidioides spp. are ______ and ________ with empty cells.

barrel-shaped alternate

How are C. neoformans and C gattii distinguished by growth

by growth features on canavanine-glycine-bromomethyl blue agar

T. rubrum culture plate

colonial morphology that is flat to cottony, and raised and ruffled at its center. The frontal coloration can range from a white to bright yellowish-beige and even to a red-violet color. From the reverse, the colonies display a coloration that is a light yellowish to brown, or reddish brown.

Saccharomyces cerevisiae

colonizer of mucosal surfaces and is part of the normal flora of the gastrointestinal tract, the respiratory tract, and the vagina

Scedosporium apiospermum/boydii is more of a moderately rapid growing dematiaceous mold whose

conidia lack septae. Its hyphae are nonpigmented but its microconidia (seen only in culture) are melanized. The mold has a light gray or brown surface in either state.

Common routes of exposure to cryptococcus is...

contaminated soil and bird dropping

Culture of infected CFS for Cryptococcus yields...

cream, colored colonies in about 3-7 days, while staining with India Ink permits rapid identification of the Cryptococcus in direct CSF smears

Dimorphic fungi: P. brasiliensis Microscopically

cultured mold reveals septate, hyaline hyphae with terminal and intercalary chlamydospores, and infrequent pear-shaped microconidia arranged along the hyphae. The definitive identification requires conversion of the mold form to the yeast form.

Opportunistic infections from Fusarium spp. frequently begin as

cutaneous infections which manifest clinically as painful, erythematous or necrotic nodules that enlarge and ulcerate. The fungi can disseminate to the lungs, kidneys, and other organs.

Dermatophytes are uniformly resistant to

cyclohexamide

Lomentospora prolificans growth is inhibited by... L. prolificans is intrinsically resistant to

cycloheximide and it has no sexual state amphotericin B as well as the azoles and echinocandins, which makes antifungal therapy ineffective.

Aspergillus niger cultures have a

dark brown to black surface due to the dark pigmentation of the conidia, but the reverse side is light-colored or white.

Coccidiodes lactophenol cotton blue preparation

demonstrating arthroconidia. The average arthroconidia measures 3.0 x 4.5 µm, and is barrel-shaped.

Dimorphic fungi - Sporothrix schenckii produces

elongated (cigar-shaped) yeast cells that measure 4-6 µm and bud at a narrow base. The mold form grows moderately to rapidly when cultured at 25-30ºC. The colonies are moist and white to pale orange, initially, turning brown with age. Very delicate, hyaline, septate hyphae are produced, and conidiophores are often seen with clusters (rosettes) of microconidia surrounding their tips

Dimorphic fungi -Talaromyces marneffei produces

elongated, ovoid, small (3-5 µm) yeast that divide by fission rather than by budding. They are often found within histiocytes. T. marneffei forms rapidly growing tan mold colonies that are initially powdery or velvety on the surface and become colored with maturity (typically blue or green centrally) when it is cultured at 25-30ºC. Additionally, a red pigment diffuses into the agar around and underneath the colonies. The yeast colonies are off-white to pink and consist of small (3-5 µm) oval yeast-like cells that reproduce by fission rather than by budding.

The most important disease caused by S. cerevisiae

fungemia It occurs in immunocompromised and critically ill patients. Saccharomyces infection is clinically indistinguishable from invasive candidiasis. Fever is common and chorioretinitis may occur.

Fusarium spp. pathogens produce characteristic

fusoid or sickle-shaped macroconidia when cultured on synthetic media, but the tissue forms of these fungi are purely hyphal. Fusoid conidia can also be seen in smears from blood cultures growing these organisms.

Lomentospora prolificans has a _______ surface and reverse while Scedosporium apiospermim has a _______ surface.

gray or black light gray or brown

Dermatophytes are keratinophilic, which means

hat they are able to digest keratin as a nutrient source using keratinases. This special ability is the source of their pathogenicity and thus most infections are limited to superficial keratinized structures such as hair, nails, and the stratum corneum of skin

Aspergillus spp

hyaline septate molds found in soil, decaying organic matter or as plant pathogens. We all regularly breathe in the conidia of Aspergillus spp., but those with weakened immune systems and lung disease are at risk for disease

C. gattii is associated with infections in...

immunocompetent

C. neoformans is associated with infection in...

immunocompromised

When disseminated infection occurs, Blastomyces spp

it most often involves the skin or mucous membranes of the nasopharynx and mouth. Other common sites of disseminated infection include the bones, prostate, and CNS. Diagnosis can also be made with an antigen test performed on urine or serum.

Stain used for Trichosporon

lactophenol cotton blue

Analysis of CSF due to Cryptococcus usually reveals...

low white blood cell count, low glucose, and elevated protein, but could also be normal in approximately 25-30% of the cases

T. tonsurans lactophenol cotton blue preparation

macroconidia and filamentous hyphae.

Paracoccidioides brasiliensis produces large, round yeast cells (10-50 µm) with circumferential budding, giving the appearance of a

mariner's wheel (methenamine silver stain) in tissue sections or primary wet preparations. The daughter cells bud on a narrow base from the mother cell.

Dermatophyte: Trichophyton tonsurans is unique because

marked sized and morphological variability of its microconidia which may be round, tear shaped, cigar shaped, or swollen and enlarged.

lactophenol cotton blue preparation of S. schenckii

ovoid or cigar-shaped conidia, some of which arise from the septate hyphae individually or in clusters, while, the conidiophore is seen in the center topped by a cluster of conidia.

patients at risk for trichosporonosis

patients who are immunosuppressed in the setting of hematologic or solid organ malignancies or solid organ transplantation those with AIDS, extensive burns, intravascular catheters, those receiving steroids, or undergoing heart valve surgeries.

Aspergillus fumigatus produces a distinct row of _______

phialides

Aspergillus flavus and niger sporulate from ________ distributed around the entire circumference of the ______.

phialides vesicle

Dimorphic fungi-Blastomyces spp.

produce large (size), broad-based budding yeast in tissue. The yeast cell walls are thick and double contoured. When incubated at 25 - 30°C, 'Blastomyces" spp. are slow growing and produce a white, cottony mycelium that darkens to tan with age

Trichosporon spp. characterized by

production of true hyphae and pseudohyphae, arthroconidia and blastoconidia

The hyphae of the Fusarium spp.

re 3 to 8 µm in width, are septate, branched and haphazardly dispersed throughout the lesions. The hyphal branches characteristically arise at right angles from parent hyphae. The hyphae cannot be reliably distinguished from those of Aspergillus spp. Definitive diagnosis requires isolation in culture.

The production of single conidia in succession both laterally and around the tip of a straight phialide is called the ________ type of sporulation, characteristic of Fonsecaea pedrosoi.

rhinocladiella *also may produce acrotheca with rhinocladiella

Saccharomyces cerevisiae characterized by

round to oval multilateral budding yeast cells and short, rudimentary pseudohyphae.

M. gypseum culture plate

showing an orange-colored wavy, though glabrous, or smoothly-textured colonial morphology

Dimorphic fungi: P. brasiliensis

slow growing mold when cultured at 25-30ºC that produces a white to tan surface and a variable texture that may be leathery, velvety, or glabrous.

Dermatophyte: Epidermophyton floccosum produces

smooth, club-shaped macroconidia with rounded ends that are arranged singly or in clusters. Each contains 2-6 cells, separated by transverse septae. Microconidia are never produced.

Feature unique to Aspergillus terreus

spherical microconidia attached to vegetative hypae in direct mount

Environmental conditions for Mucor species Aspergillus niger Epidermophyton floccosum Fusarium

stale bread Hospital construction Shared bath towels Fermenting stored grain

Dematiaceous molds are most often involved in

subcutaneous infections, although they can be isolated from a variety of specimen types from various anatomic locations.

Dermatophyte: Trichophyton rubrum produces

tear-shaped microconidia that are arranged along the conidiophore, generating a "birds on a telephone wire" appearance.

Trichosporon was initially recognized as...

the cause of white piedra, a superficial infection of the hair shaft of the scalp, face, axiallary, or pubic regions, characterized by soft white, yellow, green, or beige nodules composed of hyaline septate hyphae and arthroconidia. The disease occurs worldwide but occurs more commonly in tropical or subtropical regions.

H. capsulatum In the environment

the fungus seems to favor soil contaminated by droppings from chickens, other birds, and bats because of its high nitrogen content

Blastomyces spp. initially infect

the lungs subsequent to inhalation of infectious conidia, which are found in the environment. There it can cause acute and/or chronic infection. However, many infections remain asymptomatic. In the immunocompromised, severe pulmonary disease and disseminated infection may occur.

Dimorphic fungi -Talaromyces marneffei Microscopically

the mold colonies are composed of hyaline septate hyphae with conidiophores and metulae producing brush-like clusters of phialides. There are chains of small oval conidia that form at the terminal ends of the phialides. Thermal dimorphism should be demonstrated for correct identification.

Dimorphic fungi-Blastomyces spp. Microscopically

the mold demonstrates septate, hyaline hyphae with short unbranched conidiophores, producing single pyriform to round, smooth conidia that measure 2-10 µm. Definitive identification of Blastomyces spp. requires either conversion to its yeast form at 37ºC, or exoantigen or molecular confirmatory tests.

A common feature of dematiaceous molds is

the production of melanin pigment, which confers dark pigmentation to hyphae. Dematiaceous molds are typically dark pigmented on the surface and reverse sides of the plate, because both their hyphae and conidia are melanized. There are some species that produce only pigmented conidia, which imparts a dark top surface and a light-colored reverse.

Microscopically, Coccidioides spp. produce

thin, hyaline, septate hyphae and arthroconidia (this is seen microscopically when mold-form growth is analyzed). Mature arthroconidia are barrel-shaped and alternate with empty cells.

The rapidly growing dematiaceous molds are separated by

those with conidia with transverse septae and those with conidia with transverse and longitudinal septae. Bipolaris spp. are characterized by oval, transversely septate conidia that arise from bent (geniculate) conidiophores. The name Bipolaris is derived from the fact that these organisms produce germ tubes on both ends of their conidia in saline mounts that are incubated for 12-24 hours. Each conidium contains 3-5 septations. Curvularia spp. have transversely septated conidia that curve distinctly when they mature. Alternaria spp. produce chains of transverse and longitudinally septate (often described as muriform which resembles a brick wall) conidia that have alternating blunt and pointed ends.

What does C. albicans cause

thrush, vulvovaginitis, and esophagitis. *These diseases occur in patients in whom there has been a disruption of the bacterial microbiota or in patients with an immunocompromising condition **Cutaneous infections and onychomycosis may also be caused by Candida. Candida spp. are also important causes of intravascular access line-related fungemia, fungal endocarditis, and dissemination from the bloodstream to distant sites.

Dermatophyte infections can take many forms, including

tinea capitis (scalp ringworm), tinea corporis (ringworm), tinea cruris (jock itch), tinea pedis (athlete's foot), and tinea unguium (onychomycosis).

Clinical features of cryptococcal meningitis

typically manifest within a period of 1-2 weeks and include fever, malaise, headache, neck stiffness, photophobia, nausea, and vomiting

Fusarium spp. are

ubiquitous soil saprophytes and occasional plant pathogens. They are responsible for a variety of superficial and invasive human infectious disease.

Cryptococcus colonies

white mucoid colonies

Dimorphic fungi- capsulatum yeast cells are usually found

within histiocytes or reticuloendothelial cells. They are seen as 2-4 µm ovoid yeasts with narrow-based budding. Histoplasma capsulatum incubated at 25-30ºC is a very slow growing, powdery or cottony white mold that forms septate, hyaline hyphae. Conidiophores produce small (2-5 µm), smooth-walled microconidia or large (7-15 µm) thick-walled, spiny (tuberculate) macroconidia.

Rhodotorula spp

yeast that produce a carotenoid pigment ranging from yellowish to red that can be visualized with individual colonies. Rhodotorula can produce multilateral budding yeast cells, and occasional production of true hyphae or pseudohyphae. The budding yeast are 5-8 µm and are narrow-based. Rhodotorula can be isolated from soil, water, fruit juices, milk products, shower curtains, and toothbrushes.

Thermally dimorphic fungi produce yeast-like colonies and mold like colonies at what temp?

yeast: 37C mold: 25-30C

A. flavus produces

yellow-green to olive colonies with a light-colored reverse. Circumferential phialides are seen microscopically. Some strains are uniseriate while others are biseriate. The conidiophores of A. flavus are also often times spiny or rough.