Mycology

An aseptate mold isolated from a respiratory specimen exhibits internodal rhizoids, with sporangiophores arising from stolons between the rhizoids and bearing pyriform sporangia) What is the identity of this organism?

Absidia species

Which microscopic feature is characteristic of Syncephalastrum species?

Tubular merosporangia (finger shaped) containing chains of sporangiospores radiating around a vesicle

Which structure serves as the site of origin for erect conidiophores in Aspergillus species within the vegetative hyphae? 

Foot cell

A mold culture yields blue-green colonies with a white apron. Microscopic examination shows septate hyphae with erect conidiophores branching into metulae and phialides that form a brush-like structure. Most strains are inhibited at 37°C. Which organism does this represent?

Penicillium species

Zygomycota (Mucorales)

– found in soil

-immunocompromised patients

• Lichtheimia (Absidia), Mucor, Rhizomucor, Rhizopus

The most significant order

• Rapid growers

• Produce gray to white aerial mycelium with hyaline, sparsely septate hyphae

Asexual reproduction= Sporangiospores

Ascomycota

Produce sexual spores (ascospores)

• Microsporum, Trichophyton, Pseudallescheria boydii\

Sexual spores=Ascospores that are formed in a saclike structure known as an ascus

Basidiomycota

Not many clinically significant

• Cryptococcus neoformans var. neoformans

Clamp connections are sometimes key identifying feature

• Members of this order are typically sterile

• A portion of the hypha on one side of the septation grows out and connects to the hypha on the other side of the septation, thereby bypassing the septation

Deuteromycota (fungi imperfecti)

Largest class of etiologic agents of mycoses including cutaneous, subcutaneous and systemic disease

• Have no mode of sexual reproduction identified

Cutaneous, subcutaneous, and systemic diseases

Yeast

Single vegetative cell

Reproduce by budding or fission(budding produces blastoconidium)

No aerial hyphae (smooth/creamy/bacterial-like)

ID based on biochemical testing and molecular diagnostic methods

Mold

Aerial or vegetative hyphae(long filaments of cells joined together)

Aerial mycelia: fuzzy appearance

ID based reproductive structures that produce conidia (used to id different fungi)

Vegetative mycelia extend down into the media to absorb nutrients

Which special histopathological stain selectively stains fungal cell wall melanin brown to black?

 

Fontana-Masson stain

An India ink preparation performed on cerebrospinal fluid (CSF) reveals budding yeast cells surrounded by large, clear haloes against a dark background) This finding is characteristic of which organism?

 

Cryptococcus neoformans

A laboratory scientist performs a microscopic evaluation of a mold colony by gently pressing transparent tape against the surface of the aerial mycelium and transferring it to a slide containing lactophenol aniline blue (LPCB). What is this procedure called?

 

Cellophane tape prep

A patient presents with progressive, nonhealing skin ulcers, draining sinus tracts, and verrucous crusted nodules on the lower extremity following a puncture wound) Direct blood cultures remain negative. Which location category of mycosis is most consistent with these clinical findings?

 

Subcutaneous mycoses

Which of the following is a general cellular characteristic of all fungi?

 

Presence of a chitinous cell wall

Why is the Latin term "tinea" used in naming dermatophytic fungal infections?

 

Infections were historically believed to be caused by burrowing worms forming ring-shaped patterns.

A microscopic examination of a mold reveals hyphae with swollen branching tips that resemble moose antlers. This specific hyphal morphology is classified as:

 

Antler hyphae (favic chandeliers)

How are arthroconidia formed during asexual reproduction of fungi?

 

By the fragmentation of fertile hyphae rather than production from conidiogenous cells

What is the defining diagnostic microscopic structure created by certain Basidiomycota hyphae to bypass a septation?

 

Clamp connection

Cycloheximide is added to primary fungal isolation media (such as Sabouraud Dextrose Agar) for what specific purpose?

 

To inhibit saprophytic/contaminant molds while allowing recovery of dermatophytes and primary pathogens

What severe clinical manifestation does Pneumocystis spp. cause in immunocompromised patients, particularly those with AIDS?

Pneumonia

What microscopic morphology does Cryptococcus spp. exhibit when cultured on Cornmeal agar?

 

Blastoconidia only (no true hyphae or pseudohyphae)

What result is observed when Cryptococcus neoformans is inoculated onto a Urea agar slant?

 

Rapid positive reaction with a color change to pink/magenta

On HardyCHROM / CHROMagar Candida media, what colony color is typical for Candida albicans?

Green

What is the typical colony appearance of Candida krusei on CHROMagar Candida medium?

 

Dry, rough, pale pink colonies with spreading borders

Which feature microscopic morphology differentiates Geotrichum spp. from Trichosporon spp.?

 

Geotrichum spp. produces true hyphae that fragment into barrel-shaped arthroconidia but lacks blastoconidia

What characteristic arrangement of fungal elements is classically described on a KOH preparation of skin scrapings infected with Malassezia furfur?

 

Spaghetti and meatballs appearance (clusters of round budding yeast and short septate hyphae)

Which rapid screening test provides a presumptive identification of Candida albicans and Candida dubliniensis by detecting short hyphal projections within 2 to 3 hours?

 

Germ Tube test

How are true yeasts distinguished from yeast-like fungi regarding their reproductive capabilities?

 

True yeasts reproduce sexually by forming ascospores or basidiospores

Which clinical skin condition is caused by Malassezia furfur?

 

Tinea versicolor (pityriasis versicolor)

Microscopic evaluation of Sporothrix schenckii in its yeast phase reveals which characteristic cell morphology?

 

Small, elongated, cigar-shaped yeast cells

Histoplasma capsulatum infection is most strongly associated with exposure to soil contaminated with what material?

 

Chicken droppings and bat guano

What temperature and growth conditions are required to convert dimorphic fungi to their yeast phase in culture?

 

37°C with increased carbon dioxide (CO2)

Paracoccidioides brasiliensis is geographically restricted to which region?

 

Central and South America

In its mold phase, Talaromyces (Penicillium) marneffei displays which microscopic fungal structures?

 

Biverticillate conidiophores with terminal metulae and needle-like phialides

Coccidioides immitis is endemic to which specific ecological zone in the United States?

 

Lower Sonoran life zone, including San Joaquin Valley CA, Arizona, and SW Texas

What distinctive microscopic spore structure is produced by Histoplasma capsulatum in its mold phase?

 

Large tuberculate macroconidia with knobby surface projections

Which microscopic feature is characteristic of Blastomyces dermatitidis in tissue or yeast phase cultures?

 

Large spherical yeast cells with double-contoured walls and broad-based budding

How is fungal dimorphism defined in clinical mycology?

 

The ability of a fungus to exist in two distinct structural forms (mold and yeast) based on growth conditions

Blastomyces dermatitidis is geographically endemic to which region?

 

Mississippi and Ohio River basins

An aseptate mold isolated from a respiratory specimen exhibits internodal rhizoids, with sporangiophores arising from stolons between the rhizoids and bearing pyriform sporangia) What is the identity of this organism?

 

Absidia species

Which microscopic feature is characteristic of Syncephalastrum species?

 

Tubular merosporangia (finger shaped) containing chains of sporangiospores radiating around a vesicle

Which structure serves as the site of origin for erect conidiophores in Aspergillus species within the vegetative hyphae?

 

Foot cell

A mold culture yields blue-green colonies with a white apron. Microscopic examination shows septate hyphae with erect conidiophores branching into metulae and phialides that form a brush-like structure. Most strains are inhibited at 37°C. Which organism does this represent?

 

Penicillium species

Which microscopic feature distinguishes uniseriate from biseriate Aspergillus species?

 

Uniseriate phialides attach directly to the vesicle, whereas biseriate phialides arise from an intermediate support cell called a metula)

What is the characteristic microscopic morphology of macroconidia produced by Fusarium species?

 

Banana or canoe shape with multiple cells

Which Aspergillus species is most commonly isolated from clinical cases of invasive aspergillosis?

 

Aspergillus fumigatus

A fungal isolate shows flat, sandy-to-powdery tan colonies. Microscopic exam exhibits annellides with bowling-pin shape and rough, spiky (echinulate) conidia with flattened bases borne in chains. Which organism is this?

 

Scopulariopsis species

A medical laboratory scientist notes a rapid-growing mold covering an entire Sabouraud dextrose agar plate within 4 days with thick woolly mycelia) Microscopic review demonstrates wide, clear hyphae with no cross-walls and sporangiophores lacking rhizoids at their base. How should the scientist differentiate this isolate from Rhizopus?

 

By noting the total absence of rhizoids and stolons in Mucor, whereas Rhizopus possesses nodal rhizoids directly below sporangiophores

A skin biopsy specimen yields a septate hyaline mold with single-celled pyriform or clavate conidia featuring flat (truncate) bases, resting directly on hyphae or short pedicels. The culture resembles a dermatophyte. Which fungus is this?

 

Chrysosporium species

If Cryptococcus is suspected

India Ink

Colony Morphology yeast

Growth in 2-3 days

• BAP@ 25-37°C; best at 30°C

• Smooth/mucoid/butter-like

• White, cream, tan (some pink!)

• Some phaeoid (dark pigment)

• May be filamentous (FEET ON AGAR!)

Cornmeal-Tween 80 Agar yeast

Coverslip the agar after inoculation

• Growth in 1-2 days

• 25-37°C; best at 30°C

• Observe microscopically on cover slip

• Blastoconidia

• Pseudohyphae

• Chlamydoconidia

• Arthrospores

Germ Tube Production

Differentiates Candida from other yeasts

(+) Candida albicans and Candida dubliensis

Urease

Positive (pink):

• Cryptococcus sp. (rapid)

• Trichosporon sp.

• Rhodotorula sp.

• Negative (yellow):

• Candida sp.

• Geotrichum sp.

India Ink

Capsule detected surrounding the

budding yeast in CSF with India Ink

• Background is black/dark and clear, unstained halos are seen in individual yeast cells

• Positive (light halo on black background):

• Cryptococcus sp.

Lactophenol Cotton Blue (LPCB)

Used in wet mounts

• Cotton Blue

• Acidic dye that binds to chitin

• Stains hyphae, conidia and spores

• Phenol

• Disinfectant and fungicidal agent to kill live orgs

• Lactic Acid

• Preserves fungal morphology

Rapid Trehalose Assimilation

Aids in detection of Candida glabrata

• Identifies yeasts that can utilize/hydrolyze the sugar trehalose more quickly than other Candida species

• Incubate inoculated broth at 42°C for 3 hours

• Color changes from blue to yellow

when positive

Candida albicans

Candidia tropicalis

Candidia krusei

Candidia glabarata

Candidiasis Mucocutaneous

Most common Candidiasis

Thrush (oral)

Vaginitis

Bronchial/Pulmonary

Can be chronic

Cutaneous

Areas of profuse sweating

Areas of water immersion

Skin

Diaper Rash

Nails - Onychomycosis

Systemic

Most detrimental

UTI

Endocarditis

Septicemia

CANDIDA ALBICANS Identification

Gram Positive Organism

• Large

• Germ Tube (+)

• Growth at 42C

C.dublin… and c.para

no groth past 37

• C. neoforman

major cause of opportunistic infections in AIDS patients

• Commonly found in soil contaminated with pigeon droppings

• Acquired by inhalation

Surrounded by capsule which gives characteristic mucoid appearance

India Ink or latex

• C. neoforman identification

Produce blastoconidia only

• No true hyphae or pseudohyphae on

cornmeal agar

• Cryptococcal antigen assay detect

neoformans and gattii in CSF and

serum

Cryptococcus neoformans vs. gattii

Identification

Use CGB agar or PCR

Trichosporon spp

Opportunistic systemic pathogen= Rare, but fatal

• Immunocompromised host with

hematologic disorders, malignancies,

chemotherapy

• Causes white piedra

• Occurs on the hair shaft

• Characterized by soft mycelial mat

surrounding hair of scalp, face & pubic

region

An isolate from a toe web lesion (Tinea pedis) produces fluffy white colonies with a deep wine-red reverse. Microscopic prep shows tear-shaped microconidia along the hyphae ("red birds on a wire"). The hair perforation test is negative and urea is not hydrolyzed. How should the laboratory specialist classify this organism's diagnostic characteristics?

 

T. rubrum can infect hair, skin, and nails, but it is Wood's lamp negative, urea negative, and hair perforation negative

Which clinically significant dermatophyte species does NOT produce microconidia?

 

Epidermophyton floccosum

Which dermatophyte genus is known to infect skin and nails, but does NOT infect hair?

 

Epidermophyton

Microconidia arranged in a classic "red birds on a wire" pattern are characteristic of which species?

 

Trichophyton rubrum

A mold isolated from skin scrapings forms khaki-colored, suede-like colonies with a raised center. Microscopic exam reveals smooth, thin-walled macroconidia in clusters ("beaver tail") and an absence of microconidia. What is the identity of this isolate?

 

Epidermophyton floccosum

A diagnostic lab receives a skin scraping. Direct KOH mount displays septate hyphae. Culture on Mycosel agar yields flat, cinnamon-brown, suede-like colonies within 7 days. Microscopic mount reveals abundant thin-walled, elliptical macroconidia with 4 to 6 cells. Hair perforation is negative and rice grain media shows poor growth. How should the technologist resolve the identification?

 

Identify as Nannizzia gypsea (Microsporum gypseum) based on thin-walled elliptical macroconidia and brown colony morphology

A slow-growing dermatophyte isolated from a scalp infection forms greyish-white downy colonies with a reddish-brown reverse. Macroconidia and microconidia are rarely seen, but terminal chlamydospores are present. Growth on rice grain media is negative. What is the organism?

 

Microsporum audouinii

A specimen collected from an infected nail bed yields a mold. Microscopic evaluation demonstrates broad, thin-walled, club-shaped macroconidia produced directly from hyphae without any microconidia. Based on anatomical tropism and morphology, why is this organism categorized as Epidermophyton floccosum?

 

It infects skin and nails but cannot invade hair tissue

A suede-like, flat dermatophyte colony produces symmetrical, thin-walled macroconidia containing 4 to 6 cells. Rice grain media shows poor to negative growth, and hair perforation is negative. What is this organism?

 

Microsporum gypseum

A suspected fungal isolate fails to grow on Trichophyton Agar No. 1 (vitamin-free agar) unless thiamine is added. Microscopic examination demonstrates tear-shaped (pyriform) microconidia born at right angles to hyphae. What is the organism?

 

Trichophyton tonsurans