#3: 🍄Mycology - isolation methods and culture media

Inoculate media that lacks standard antibiotics

A medical technologist suspects that a clinical specimen contains Nocardia species or other filamentous bacteria. Which of the following modifications to the isolation protocol must be made to successfully recover the organism?

Isolation of Cryptococcus neoformans and C. gattii

A medical technologist is selecting a primary culture medium to explicitly isolate Cryptococcus neoformans and Cryptococcus gattii from a spinal fluid specimen. Which of the following describes the primary purpose of Birdseed agar?

Phenol oxidase

Birdseed agar utilizes caffeic acid derived from Guizotia abyssinica seeds. Which specific enzyme produced by Cryptococcus species metabolizes this substrate to yield brown-pigmented colonies?

Melanin

When Cryptococcus neoformans breaks down caffeic acid on Birdseed agar, what specific end-product compound is produced that causes the characteristic pigmentation of the colonies?

Enhances the melanization of some strains of C. neoformans

Birdseed agar formulations frequently include a specific organic compound that acts as an enhancer. What is the factual role of creatinine within this medium?

Isolation and differentiation of Candida species

A supervisor asks a trainee to prepare a batch of Bismuth Sulfite-Glucose-Glycine Yeast (BIGGY) agar. Which of the following options defines the primary purpose of this medium?

Bismuth sulfide

On BIGGY agar, Candida species produce a distinct brown-to-black colonial pigmentation. This color change is a direct result of the reduction of bismuth sulfite into which of the following compounds?

Inhibitor of bacterial growth

Bismuth sulfite is a foundational component of BIGGY agar. Apart from serving as a vital differential substrate for reduction reactions, what secondary function does it perform in the medium?

Candida albicans

A medical technologist observes yeast colonies on BIGGY agar that present with a brown-to-black color but show absolutely no pigment diffusion into the surrounding agar and no surface sheen. Which organism matches this descriptive profile?

Candida tropicalis

During a culture review, an isolate on BIGGY agar forms dark brown colonies with distinctly black centers, visible black pigment diffusion spreading into the surrounding agar, and a prominent sheen. Which pathogen is indicated?

Isolation of all fungi including fastidious dimorphic fungi and processing of sterile specimens

When handling critical sterile specimens where dimorphic pathogens are suspected, a medical technologist inoculates a tube of Brain Heart Infusion (BHI) agar supplemented with antibiotics. What is the designated purpose of this medium?

Chloramphenicol and gentamicin

BHI agar with antibiotics uses a multi-drug approach to prevent sample overgrowth. Which specific pair of antimicrobials is incorporated into this medium to act as the inhibitors of bacterial growth?

Inhibiting overgrowth of saprophytic fungi

To ensure clean recovery from non-sterile sites, BHI agar incorporates cycloheximide. What is the explicit purpose of adding cycloheximide to this formulation?

Differential medium to distinguish C. neoformans from C. gattii

A reference laboratory receives a urea-positive, encapsulated yeast isolate. The technologist sets up a Canavanine-glycine-bromthymol blue (CGB) agar slant. What is the exact purpose of this medium?

Cobalt blue

A clinical isolate of Cryptococcus gattii (serotypes B and C) is inoculated onto a CGB agar slant. What characteristic color shift will this organism produce in the medium?

Greenish yellow

When inoculated onto CGB agar, Cryptococcus neoformans var. grubii (serotype A) and Cryptococcus neoformansvar. neoformans (serotype D) fail to utilize the substrates in the same manner as C. gattii. What color do these variants leave the medium?

Identification of Cryptococcus, Trichosporon, and Rhodotorula spp.

A medical technologist isolates an unknown yeast and inoculates a slant of Christensen's urea agar. According to your review sheet, what is the primary diagnostic purpose of this medium?

Trichophyton mentagrophytes from Trichophyton rubrum

Apart from identifying specific yeast genera, Christensen's urea agar serves a critical secondary purpose in a dermatophyte workup. It is used to separate which two look-alike species?

Cultivation and differentiation of T. mentagrophytes from T. rubrum on the basis of pigment production

A technologist needs to differentiate two closely related Trichophyton species and selects Cornmeal agar supplemented with 1% dextrose. What is the explicit purpose of this medium?

Differentiation of Candida species on the basis of morphological characteristics

A medical technologist prepares a Dalmau plate using Cornmeal agar with Tween 80. What is the primary purpose of selecting this specific medium formulation?

Pseudohyphae, chlamydospores, and arthrospores

When evaluating a Candida isolate grown under a coverslip on Cornmeal agar with Tween 80, the technologist is explicitly looking for the demonstration of which microscopic features?

Differentiation of Aspergillus spp.

An environmental sample yields a fuzzy, colored mold colony showing distinct phialides and chains of conidia. To definitively classify the isolate, the technologist subcultures it onto Czapek-Dox agar. What is the main purpose of this medium?

Inhibiting saprophytic molds and Gram-negative bacteria while turning from yellow to red with dermatophyte growth

A patient presenting with suspected ringworm provides hair and skin scrapings. The technologist inoculates a Dermatophyte Test Medium (DTM) slant. What is the fundamental operational purpose of DTM?

Cycloheximide and chloramphenicol

DTM relies on chemical selectants to ensure that background contaminants do not obscure the slow growth of dermatophytes. Which specific agents are present in DTM to inhibit saprophytic molds and Gram-negative bacteria, respectively?

Medium is yellow and turns red

A medical technologist monitors a DTM slant daily. As a dermatophyte grows and produces alkaline metabolites, what specific color change occurs in the medium?

Used for the isolation and growth of lipodependent Malassezia spp.

Skin scrapings from a patient with tinea versicolor are submitted to the bench. The medical technologist selects Leeming and Notman medium. What is the primary purpose of this highly specialized agar?

Selective general-purpose medium used for the isolation of fungi from contaminated specimens

A heavily soiled skin sample contaminated with soil bacteria and environmental molds is received. The technologist decides to use Littman oxgall agar. What is the primary purpose of this medium?

Crystal violet and streptomycin

Littman oxgall agar effectively eliminates background bacterial contamination using a specific combination of selective ingredients. Which two compounds are used in this medium to inhibit bacteria?

Oxgall

When a specimen contains fast-growing, aggressive environmental fungi, Littman oxgall agar prevents them from overtaking the plate. What component within the medium acts to restrict the spreading of fungal colonies?

Isolation of dermatophytes and other pathogenic fungi from specimens contaminated with saprophytic fungi and bacteria

A medical technologist prepares to plate a non-sterile specimen contaminated with saprophytic fungi and bacteria. Which option describes the primary purpose of choosing Mycosel or Mycobiotic agar?

Cycloheximide and chloramphenicol

To maintain its strict selectivity for dermatophytes and pathogenic fungi while holding back background flora, Mycosel agar contains which specific combination of antimicrobial agents?

Stimulating conidium production by fungi and stimulating pigment production in some dermatophytes

A subculture of a mold isolate is transferred onto Potato Dextrose agar. What is the primary purpose of this medium in a diagnostic mycology lab?

Tartaric acid

Instead of using standard broad-spectrum commercial antibiotics, Potato Dextrose agar relies on a unique chemical mechanism to prevent bacterial overgrowth. What ingredient is added to accomplish this?

Used to differentiate M. audouinii from M. canis

A medical technologist isolates a sterile white mold that could be a dermatophyte capable of causing tinea capitis. The organism is inoculated onto Rice Medium. What is the precise purpose of this test medium?

Used for the recovery of saprobic and pathogenic fungi

Sabouraud Dextrose Agar (SDA) is the most ubiquitous medium on the mycology bench. What is the standard purpose of utilizing unsupplemented SDA?

Saprobes may be inhibited

While baseline SDA is a general-purpose recovery medium, it can be modified. According to the table, what is the consequence if SDA is incorporated with antimicrobials?

Aspergillus fumigatus

Cycloheximide is commonly incorporated into fungal culture media to suppress rapidly growing saprobic fungi. However, it is known to inhibit several significant human pathogens. Which of the following organisms would be inhibited by the presence of cycloheximide?
B. Blastomyces dermatitidis
C. Histoplasma capsulatum
D. Sporothrix schenckii

It inhibits conidiation in the mold form

While an enriched medium containing blood promotes the growth and recovery of very fastidious thermally dimorphic fungi, it carries which of the following diagnostic disadvantages when inspecting the mold phase?
A. It induces complete cell wall lysis
C. It leads to rapid overgrowth by saprobes
D. It prevents the yeast-to-mold transition

Cycloheximide

When working with a suspected case of mucormycosis, a medical technologist should ensure that the culture media chosen lacks which of the following selective agents?
A. Chloramphenicol
C. Gentamicin
D. Tobramycin

Aerobic actinomycetes

Antibiotics such as chloramphenicol and gentamicin are standard components in fungal isolation media. Apart from routine bacterial contaminants, these agents are highly likely to prevent the growth of which group of clinically significant organisms?
B. Dermatophytic molds
C. Lipodependent yeasts
D. Thermally dimorphic fungi

Birdseed agar

Which medium utilizes caffeic acid to detect phenol oxidase activity, causing Cryptococcus neoformans to produce brown-pigmented melanin colonies?

Sabouraud dextrose agar (SDA)

What is the standard, basic recovery medium used for both saprobic and pathogenic fungi, which can be combined with antimicrobials if needed?

Rice medium

Which specific medium is historically utilized in the diagnostic laboratory to reliably differentiate Microsporum audouinii from Microsporum canis?

Potato dextrose

Which medium is used to stimulate fungal conidium and pigment production, using tartaric acid to lower pH and inhibit bacterial overgrowth?

Mucosal or Mycobiotic agar

Which classic fungal isolation medium contains a baseline mix of both cycloheximide (to inhibit saprophytic molds) and chloramphenicol (to inhibit bacteria) for isolating dermatophytes?

Littman oxgall agar

Which selective general-purpose medium incorporates oxgall for the explicit purpose of restricting the spatial spreading of fungal colonies from crowded specimens?

Leeming and Norman medium

Which specialized medium contains essential fatty acids required to isolate and grow lipodependent Malassezia species?

(DTM) Dermatophyte Test Medium

Which diagnostic medium contains cycloheximide, chloramphenicol, and a pH indicator that changes from yellow to intense red when a dermatophyte grows?

Czapek Dox Agar

Which agar formulation is designated specifically as the standard medium for the differential cultivation and growth of Aspergillus species?

Cornmeal agar with Tween 80

Which medium is explicitly used to differentiate Candida species by encouraging the morphological development of pseudohyphae, chlamydospores, and arthrospores?

Cornmeal agar with 1% dextrose

Which medium is formulated with a specific carbohydrate concentration to stimulate and differentiate Trichophyton rubrum based on its characteristic red pigment production?

Christensen’s urea agar

Which medium is utilized for the presumptive identification of Cryptococcus, Trichosporon, and Rhodotorula, as well as separating Trichophyton mentagrophytes from Trichophyton rubrum via enzyme activity?

Canavanine-glycine-bromthymol blue agar

Which specific differential medium turns cobalt blue in the presence of Cryptococcus gattii, while leaving Cryptococcus neoformans as greenish-yellow?

Brain heart infusion agar with antibiotics

Which medium is used primarily for the isolation of very fastidious dimorphic fungi and sterile specimens, and contains chloramphenicol and gentamicin to inhibit bacteria?

Bismuth sulfite-glucose-glycine-yeast agar (BIGGY)

On which selective and differential medium do Candida species reduce bismuth sulfite, resulting in brown-to-black colonies?

Birdseed agar (Niger seed agar) Caffeic agar

Which medium utilizes caffeic acid to detect phenol oxidase activity, causing Cryptococcus neoformans to produce brown-pigmented melanin colonies?