Exam Prep
Fungal lab methods, yeasts, superficial and cutaneous fungi, opportunistic molds and dimorphic fungi.
Independent practice questions written by Labologics. Not affiliated with DHA, DOH (formerly HAAD), SCFHS, Prometric or any exam body. Not recalled exam questions.
Which statement about yeasts is correct?
Answer: A — They are unicellular and reproduce mainly by budding
Molds are multicellular and form hyphae. Dimorphic fungi grow as molds at 25 C and as yeasts at 37 C (in tissue).
Reference: Larone's Medically Important Fungi: A Guide to Identification
10% KOH is used on skin, hair and nail samples to:
Answer: B — Dissolve keratin and cellular material so fungal elements are easier to see
Calcofluor white can be added; it binds chitin and fluoresces under UV light, increasing sensitivity.
Reference: Larone's Medically Important Fungi: A Guide to Identification
The standard medium for primary isolation of fungi is:
Answer: C — Sabouraud dextrose agar
Its low pH and high sugar favor fungi. Chloramphenicol inhibits bacteria; cycloheximide inhibits saprophytic molds but also some pathogens such as Cryptococcus.
Reference: Larone's Medically Important Fungi: A Guide to Identification
Which stains are commonly used to show fungi in tissue sections?
Answer: D — GMS (Grocott methenamine silver) and PAS
GMS stains fungal walls black; PAS stains them magenta.
Reference: Larone's Medically Important Fungi: A Guide to Identification
Dimorphic fungi grow as:
Answer: A — Molds at 25 C and yeasts (or spherules) at 37 C / in tissue
'Mold in the cold, yeast in the heat'. Examples: Histoplasma, Blastomyces, Coccidioides, Paracoccidioides, Talaromyces, Sporothrix.
Reference: Larone's Medically Important Fungi: A Guide to Identification
Why must a suspected Coccidioides mold culture be handled only in a biological safety cabinet with the plate sealed?
Answer: B — Its arthroconidia are easily airborne and highly infectious
Coccidioides and Histoplasma molds are major laboratory infection risks.
Reference: Mahon & Lehman: Textbook of Diagnostic Microbiology
A suitable surface disinfectant for the mycology bench is:
Answer: D — 70% ethanol or a fresh hypochlorite solution
Follow local biosafety policy; hypochlorite is better against heavy organic soiling.
Reference: Mahon & Lehman: Textbook of Diagnostic Microbiology
Which test presumptively identifies Candida albicans in 2-3 hours?
Answer: C — Germ tube test in serum at 37 C
True germ tubes have no constriction at the point of origin. C. dubliniensis is also positive. Chlamydospores on cornmeal agar also support C. albicans.
Reference: Larone's Medically Important Fungi: A Guide to Identification
White, curd-like patches in the mouth of an infant or immunocompromised patient are typical of:
Answer: D — Oral candidiasis (thrush)
Candida appears as Gram-positive budding yeasts with pseudohyphae.
Reference: Larone's Medically Important Fungi: A Guide to Identification
Which Candida species is an emerging multidrug-resistant hospital pathogen that can be misidentified by older methods?
Answer: A — Candida auris
It spreads in healthcare settings. Identify it by MALDI-TOF or molecular methods.
Reference: Mahon & Lehman: Textbook of Diagnostic Microbiology
An HIV patient with headache has encapsulated yeasts in CSF. The most sensitive rapid test is:
Answer: B — Cryptococcal antigen (CrAg) test
India ink shows the capsule as a clear halo but is less sensitive. Cryptococcus is urease positive and forms brown colonies on birdseed (niger seed) agar.
Reference: Mahon & Lehman: Textbook of Diagnostic Microbiology
The main virulence factor of Cryptococcus neoformans that is seen with India ink is its:
Answer: C — Polysaccharide capsule
The capsule is antiphagocytic. Infection follows inhalation of yeasts from pigeon droppings.
Reference: Larone's Medically Important Fungi: A Guide to Identification
Pneumocystis jirovecii pneumonia is best diagnosed from:
Answer: D — Bronchoalveolar lavage stained with GMS, Giemsa or immunofluorescence (or PCR)
Pneumocystis cannot be cultured; it occurs in people with HIV and CD4 below 200 cells/uL.
Reference: Mahon & Lehman: Textbook of Diagnostic Microbiology
A yeast forming pink to coral colonies is most likely:
Answer: A — Rhodotorula
Rhodotorula is an occasional opportunist linked to catheters.
Reference: Larone's Medically Important Fungi: A Guide to Identification
'Spaghetti and meatballs' (short hyphae and round yeasts) in skin scrapings indicate:
Answer: B — Malassezia furfur (pityriasis versicolor)
Malassezia needs lipids; culture needs olive oil overlay or special media.
Reference: Larone's Medically Important Fungi: A Guide to Identification
Painless brown-black patches on the palm caused by a pigmented yeast-like fungus are tinea nigra, caused by:
Answer: C — Hortaea werneckii
Black piedra (hard black nodules on hair) is Piedraia hortae; white piedra (soft nodules) is Trichosporon.
Reference: Larone's Medically Important Fungi: A Guide to Identification
Dermatophytes infect:
Answer: D — Keratinized tissue: skin, hair and nails
The genera are Trichophyton, Microsporum and Epidermophyton.
Reference: Larone's Medically Important Fungi: A Guide to Identification
The most common cause of athlete's foot (tinea pedis) and nail infection is:
Answer: A — Trichophyton rubrum
T. rubrum often produces a red pigment on the reverse of the colony.
Reference: Larone's Medically Important Fungi: A Guide to Identification
Infected hair that fluoresces yellow-green under a Wood's lamp suggests:
Answer: B — Microsporum canis
M. canis is zoophilic (cats, dogs) and produces spindle-shaped macroconidia.
Reference: Larone's Medically Important Fungi: A Guide to Identification
Which dermatophyte produces club-shaped macroconidia, no microconidia, and does not infect hair?
Answer: C — Epidermophyton floccosum
It infects skin and nails only.
Reference: Larone's Medically Important Fungi: A Guide to Identification
Narrow septate hyphae with acute-angle (about 45 degree) dichotomous branching in tissue suggest:
Answer: D — Aspergillus
Galactomannan antigen supports invasive aspergillosis in neutropenic patients. A. fumigatus is the most common species.
Reference: Larone's Medically Important Fungi: A Guide to Identification
Invasive aspergillosis is most typical in:
Answer: A — Patients with prolonged neutropenia, e.g., after chemotherapy or stem cell transplant
Aspergillus can also form a fungus ball (aspergilloma) in old lung cavities.
Reference: Mahon & Lehman: Textbook of Diagnostic Microbiology
Broad, ribbon-like, pauci-septate (aseptate) hyphae with right-angle branching in necrotic tissue suggest:
Answer: B — Mucormycosis (Rhizopus, Mucor)
Mucormycosis is linked to uncontrolled diabetes (especially ketoacidosis), steroids and iron overload; it caused many cases after COVID-19.
Reference: Larone's Medically Important Fungi: A Guide to Identification
Which Mucorales genus has rhizoids located directly beneath the sporangiophore?
Answer: C — Rhizopus
Mucor has no rhizoids. Mucorales grow rapidly as fluffy 'lid-lifter' colonies.
Reference: Larone's Medically Important Fungi: A Guide to Identification
Multicelled, banana (sickle)-shaped macroconidia identify:
Answer: D — Fusarium
Fusarium can cause keratitis and disseminated infection in neutropenia; colonies are often pink to lavender.
Reference: Larone's Medically Important Fungi: A Guide to Identification
Conidiophores with brush-like branches (penicillus) bearing chains of conidia identify:
Answer: A — Penicillium
Penicillium is usually a contaminant. Talaromyces marneffei (formerly Penicillium marneffei) is dimorphic with a red diffusible pigment.
Reference: Larone's Medically Important Fungi: A Guide to Identification
Small intracellular yeasts inside macrophages, from a patient exposed to bird or bat droppings, suggest:
Answer: B — Histoplasma capsulatum
In culture at 25 C it forms tuberculate macroconidia. Histoplasmosis is also called Darling's disease.
Reference: Larone's Medically Important Fungi: A Guide to Identification
Large thick-walled yeasts with single BROAD-BASED buds in tissue suggest:
Answer: C — Blastomyces dermatitidis
Paracoccidioides shows multiple buds ('pilot's wheel'). Blastomycosis is also called Chicago disease.
Reference: Larone's Medically Important Fungi: A Guide to Identification
Spherules containing endospores in tissue are characteristic of:
Answer: D — Coccidioides
In culture it forms barrel-shaped alternating arthroconidia, which are highly infectious.
Reference: Larone's Medically Important Fungi: A Guide to Identification
A gardener develops nodules spreading up the arm along lymphatics after a thorn prick. The likely cause is:
Answer: A — Sporothrix schenckii
Tissue shows cigar-shaped yeasts; this is 'rose gardener's disease'.
Reference: Larone's Medically Important Fungi: A Guide to Identification
Black grains discharged from a chronic foot swelling (Madura foot) suggest eumycetoma caused by:
Answer: B — Madurella mycetomatis
Actinomycetoma (bacterial, e.g., Nocardia) usually gives pale or red grains; the distinction guides treatment.
Reference: Mahon & Lehman: Textbook of Diagnostic Microbiology
Fungal meningitis typically shows which CSF pattern?
Answer: C — Lymphocytes, low glucose, high protein
This pattern resembles tuberculous meningitis; cryptococcal antigen testing and culture are needed.
Reference: Mahon & Lehman: Textbook of Diagnostic Microbiology