Mycology Practice Questions

Q: Which of the following is a dimorphic fungus?

Sporothrix schenckii. **Explanation:** **Dimorphic fungi** are unique pathogens that exist in two distinct morphological forms depending on environmental conditions, primarily temperature (**Thermal Dimorphism**). They exist as **molds** (hyphae) in the cold/environment (25°C) and as **yeasts** in the warm host tissue (37°C). **Why Sporothrix schenckii is correct:** *Sporothrix schenckii* is a classic dimorphic fungus. In the environment (on decaying vegetation or thorns), it grows as a mold with septate hyphae and "rosette-like" conidia. Once inoculated into the human body, it converts into a **cigar-shaped yeast**. **Analysis of Incorrect Options:** * **Rhizopus (Option A):** This is a **Zygomycete** (Phycomycete). It is a monomorphic mold characterized by broad, non-septate hyphae and is not dimorphic. * **Tinea versicolor (Option B):** Caused by *Malassezia furfur*, this is a **dimorphic-like** yeast that is part of normal skin flora. However, in medical microbiology, it is classified as a yeast that produces short hyphae (spaghetti and meatballs appearance) under specific conditions, but it is not categorized under the "classic systemic dimorphic fungi." * **Microsporum (Option D):** This is a **Dermatophyte**. Dermatophytes are monomorphic filamentous fungi (molds) that infect keratinized tissues (skin, hair, nails). **NEET-PG High-Yield Pearls:** 1. **Mnemonic for Dimorphic Fungi:** "**B**ody **H**eat **P**robably **S**hapes **C**occidioides" (**B**lastomyces, **H**istoplasma, **P**aracoccidioides, **S**porothrix, **C**occidioides). *Note: Penicillium (Talaromyces) marneffei is also dimorphic.* 2. **Sporothrix Clinical Presentation:** Known as **"Rose Gardener’s Disease,"** it typically presents as linear nodules along lymphatic channels (lymphocutaneous sporotrichosis) following a traumatic thorn prick. 3. **Treatment:** Oral **Itraconazole** is the drug of choice; historically, saturated solution of potassium iodide (SSKI) was used.

Q: Infected tissues demonstrating budding fungal cells are seen in which of the following conditions?

Candidiasis, cryptococcosis, and sporotrichosis. **Explanation** The presence of **budding yeast cells** in tissue is a hallmark of specific fungal infections, primarily those caused by yeasts or dimorphic fungi in their parasitic phase. **Why Option D is Correct:** * **Candidiasis:** *Candida albicans* typically shows budding yeast cells (blastoconidia) along with pseudohyphae in tissue. * **Cryptococcosis:** *Cryptococcus neoformans* is an obligate yeast characterized by narrow-based budding cells surrounded by a thick polysaccharide capsule (visualized with India ink or Mucicarmine). * **Sporotrichosis:** *Sporothrix schenckii* is a dimorphic fungus. In infected tissue (the yeast phase), it appears as small, oval, "cigar-shaped" budding cells. **Why Other Options are Incorrect:** * **Option A:** **Aspergillosis** presents as septate hyphae with acute-angle branching, not budding cells. **Coccidioidomycosis** is characterized by large **spherules** filled with endospores. * **Option B:** **Tinea versicolor** shows a "spaghetti and meatballs" appearance (short hyphae + yeast clusters), but **Tinea nigra** presents as branched, septate dematiaceous hyphae. * **Option C:** **Dermatophytosis** (Ringworm) is characterized by septate hyphae and arthroconidia in skin/hair/nails, never budding yeast cells. **High-Yield NEET-PG Pearls:** 1. **Paracoccidioidomycosis:** Look for "Pilot’s wheel" or "Mickey Mouse" appearance (multiple budding). 2. **Blastomycosis:** Characterized by large, **broad-based budding** yeast. 3. **Histoplasmosis:** Small intracellular budding yeasts within macrophages (resembles *Leishmania* but lacks a kinetoplast). 4. **Chromomycosis:** Look for **Sclerotic bodies** (Medlar bodies/copper pennies), not budding cells.

Q: Which structures can be infected by Trichophyton species?

Skin, hair, and nails. This question tests your knowledge of **Dermatophytosis**, a group of fungal infections caused by molds that require keratin for growth. These fungi are collectively known as dermatophytes and are categorized into three main genera: *Trichophyton*, *Microsporum*, and *Epidermophyton*. ### 1. Why Option A is Correct The genus **Trichophyton** is unique among dermatophytes because it possesses the enzymatic machinery to break down keratin in all three keratinized tissues. Therefore, it can infect the **skin, hair, and nails**. Common species include *T. rubrum* (the most common cause of athlete's foot) and *T. mentagrophytes*. ### 2. Why Other Options are Incorrect To differentiate the three genera, remember the tissues they **cannot** infect: * **Microsporum:** Infects **Skin and Hair**, but rarely nails. (Incorrect: Options B and C) * **Epidermophyton:** Infects **Skin and Nails**, but never hair. (Incorrect: Options C and D) ### 3. High-Yield Clinical Pearls for NEET-PG * **The "Rule of Three":** * *Trichophyton*: 3 structures (Skin, Hair, Nails) * *Microsporum*: 2 structures (Skin, Hair) * *Epidermophyton*: 2 structures (Skin, Nails) * **Tinea Capitis:** Most commonly caused by *Trichophyton* and *Microsporum*. *Epidermophyton* **never** causes Tinea Capitis because it does not infect hair. * **Most Common Dermatophyte:** *Trichophyton rubrum* is the most frequent cause of dermatophytosis worldwide. * **Diagnosis:** KOH mount showing branching hyphae and Wood’s lamp examination (Microsporum species typically fluoresce, while most Trichophyton species do not).

Q: Which of the following is NOT a dimorphic fungus?

Phialophora. ### Explanation **Concept of Dimorphism:** Dimorphic fungi are those that exist in two distinct morphological forms depending on environmental conditions (primarily temperature): they grow as **molds (hyphae)** in the environment or at 25°C, and as **yeasts** (or spherules) within the host tissues or at 37°C. A common mnemonic for this is: *"Mold in the Cold, Yeast in the Beast."* **Why Phialophora is the Correct Answer:** **Phialophora** (specifically *P. verrucosa*) is a **monomorphic** dematiaceous (pigmented) fungus. It exists only as a mold characterized by flask-shaped phialides. It is a causative agent of **Chromoblastomycosis**, where it forms characteristic **Sclerotic bodies** (Medlar bodies/Copper-penny bodies) in tissue, rather than transforming into a yeast phase. **Analysis of Incorrect Options:** * **Blastomyces dermatitidis:** A classic systemic dimorphic fungus. In tissue, it appears as characteristic **broad-based budding yeasts**. * **Histoplasma capsulatum:** A systemic dimorphic fungus found in soil with bird/bat droppings. In tissue, it appears as **small intracellular yeasts** within macrophages. * **Penicillium marneffei (now Talaromyces marneffei):** The only dimorphic species of its genus. It is an important opportunistic infection in HIV patients (Southeast Asia), showing **transverse fission** (binary fission) in its yeast phase. **High-Yield NEET-PG Pearls:** * **Systemic Dimorphic Fungi:** *Histoplasma, Blastomyces, Coccidioides* (forms spherules, not yeast), *Paracoccidioides*. * **Subcutaneous Dimorphic Fungus:** *Sporothrix schenckii* (Cigar-shaped yeasts). * **Chromoblastomycosis Key Feature:** Look for "Copper-penny bodies" or "Sclerotic bodies" in skin biopsies; these are diagnostic and represent the fungus in a non-yeast, non-mold vegetative state. * **Talaromyces marneffei:** Produces a characteristic **red diffusible pigment** on Sabouraud Dextrose Agar (SDA).

Q: Rhinosporidium seeberi is classified as which type of organism?

Mesomycetozoa. ### Explanation **Rhinosporidium seeberi** was traditionally classified as a fungus for over a century due to its morphology (production of sporangia and spores) and its staining characteristics (Gomori Methenamine Silver positive). However, modern molecular phylogenetic analysis (18S rRNA sequencing) has reclassified it into a unique group of aquatic protists known as **Mesomycetozoa** (or the DRIP clade). #### Why the Correct Option is Right: * **Mesomycetozoa:** This is a "clade" of organisms situated at the evolutionary divergence between animals and fungi. *R. seeberi* is no longer considered a true fungus because it cannot be cultured on fungal media and its cell wall lacks chitin in certain stages. #### Why Other Options are Wrong: * **Fungi:** While it mimics fungal behavior (forming large sporangia filled with endospores), it lacks ergosterol in its cell membrane and does not respond to standard antifungal therapy. * **Bacteria:** It is a complex eukaryote, significantly larger than any bacteria, and does not possess a prokaryotic cell structure. * **Protozoa:** While it is a protist, "Protozoa" is a broad, non-specific term. Mesomycetozoa is the specific, phylogenetically accurate classification required for medical examinations. #### Clinical Pearls for NEET-PG: * **Clinical Presentation:** Causes **Rhinosporidiosis**, characterized by friable, leafy, strawberry-like polypoid masses in the nose or nasopharynx. * **Transmission:** Associated with bathing in stagnant freshwater (ponds/lakes). * **Diagnosis:** Cannot be cultured. Diagnosis is via **histopathology** showing large **sporangia** (up to 350 µm) containing thousands of **endospores**. * **Treatment:** Surgical excision with wide-base cautery is the gold standard. **Dapsone** is the only medical adjunct that may prevent recurrence.

Q: Pseudohyphae are seen in which of the following fungi?

Candida. **Explanation:** **1. Why Candida is Correct:** *Candida albicans* is a polymorphic fungus, meaning it can exist in multiple morphological forms. **Pseudohyphae** are a hallmark feature of *Candida*. They are formed when yeast cells (blastoconidiospores) undergo budding but fail to detach, resulting in elongated chains of cells with constricted septations (resembling links of sausage). * **Note:** *Candida albicans* also produces true hyphae and germ tubes (at 37°C), but pseudohyphae are the classic diagnostic feature seen in clinical specimens like skin scrapings or vaginal swabs. **2. Why the Other Options are Incorrect:** * **Cryptococcus (A):** This is a strictly **monomorphic yeast**. It reproduces by budding but never forms pseudohyphae or true hyphae. Its defining feature is a thick polysaccharide capsule (visualized by India Ink). * **Rhizopus & Mucor (C & D):** These belong to the class Zygomycetes. They are **filamentous fungi** (molds) characterized by broad, **aseptate (non-septate)**, ribbon-like true hyphae that branch at right angles (90°). They do not have a yeast phase and thus do not form pseudohyphae. **3. High-Yield Clinical Pearls for NEET-PG:** * **Exception:** *Candida glabrata* is the only medically important *Candida* species that **does not** form pseudohyphae (it exists only as yeast). * **Germ Tube Test (Reynolds-Braude Phenomenon):** Positive in *C. albicans* and *C. dubliniensis*. * **Culture:** *Candida* produces creamy white colonies on Sabouraud Dextrose Agar (SDA). On Cornmeal Agar, *C. albicans* produces characteristic **Chlamydospores**. * **Morphology Mnemonic:** "Pseudohyphae = Constrictions; True Hyphae = Parallel walls."

Q: Tinea capitis is caused by which of the following fungi, except?

Epidermophyton. **Explanation:** The correct answer is **Epidermophyton**. Dermatophytes are classified into three genera based on their tissue predilection: *Trichophyton*, *Microsporum*, and *Epidermophyton*. The genus **Epidermophyton** (specifically *E. floccosum*) is unique because it infects only the **skin and nails**. It lacks the ability to invade hair follicles; therefore, it **never causes Tinea capitis**. **Analysis of Options:** * **Microsporum (Option B):** This genus infects both **hair and skin**. It is a common cause of ectothrix infections (where spores form on the outside of the hair shaft) and often presents with fluorescence under Wood’s lamp. * **Trichophyton violaceum (Option C):** This is a classic cause of **Endothrix** Tinea capitis (spores inside the hair shaft), leading to "Black Dot" Tinea capitis due to hair breakage at the surface. * **Trichophyton schoenleinii (Option D):** This is the primary causative agent of **Tinea favosa (Favus)**, characterized by yellowish cup-shaped crusts called scutula and permanent scarring alopecia. **High-Yield NEET-PG Pearls:** 1. **Rule of Three:** * *Trichophyton:* Infects Skin, Hair, and Nails. * *Microsporum:* Infects Skin and Hair (NOT nails). * *Epidermophyton:* Infects Skin and Nails (NOT hair). 2. **Most common cause of Tinea capitis worldwide:** *Trichophyton tonsurans*. 3. **Wood’s Lamp:** *Microsporum* species typically fluoresce (bright green), while most *Trichophyton* species (except *T. schoenleinii*) do not. 4. **Ectothrix vs. Endothrix:** Endothrix (e.g., *T. violaceum*) results in "Black dots"; Ectothrix (e.g., *Microsporum*) results in "Grey patches."

Q: Spindle-shaped conidia are characteristic of which fungus?

Fusarium. **Explanation:** **Fusarium** species are characterized by the production of two types of conidia: **macroconidia** and microconidia. The macroconidia are the diagnostic hallmark; they are multi-septate, hyaline, and classically described as **spindle-shaped, sickle-shaped, or canoe-shaped**. In a clinical setting, *Fusarium* is a common cause of mycotic keratitis (often associated with contact lens use) and can cause disseminated infections in immunocompromised patients, often presenting with necrotic skin lesions. **Analysis of Incorrect Options:** * **Aspergillus:** Characterized by a conidiophore ending in a swollen **vesicle** covered with phialides (sterigmata) that produce chains of round, pigmented conidia. * **Penicillium:** Exhibits a "brush-like" appearance (**penicillus**). The conidiophores branch into metulae and phialides, which bear long chains of small, spherical conidia. * **Conidiobolus:** A member of the Entomophthorales, it produces large, spherical primary mitospores that can forcibly discharge (ballistoconidia). It typically causes chronic rhinofacial subcutaneous zygomycosis. **High-Yield NEET-PG Pearls:** * **Fusarium:** Known for causing "hyalohyphomycosis." It is one of the few molds that can be recovered from **blood cultures** in disseminated cases (unlike *Aspergillus*). * **Microsporum canis:** Also produces spindle-shaped macroconidia, but these are thick-walled and found in dermatophyte cultures, not typically confused with the opportunistic *Fusarium* in systemic exams. * **Key Association:** Fusarium = Sickle/Spindle-shaped conidia + Mycotic Keratitis.

Question 1

Which of the following is a dimorphic fungus?

Accepted Answer

Sporothrix schenckii

Answer

Rhizopus

Answer

Tinea versicolor

Answer

Microsporum

Question 2

Infected tissues demonstrating budding fungal cells are seen in which of the following conditions?

Accepted Answer

Candidiasis, cryptococcosis, and sporotrichosis

Answer

Coccidioidomycosis, chromomycosis, aspergillosis

Answer

Tinea versicolor, tinea nigra, candidiasis

Answer

Blastomycosis, paracoccidioidomycosis, dermatophytosis

Question 3

Which structures can be infected by Trichophyton species?

Accepted Answer

Skin, hair, and nails

Answer

Skin and nails

Answer

Hair and nails

Answer

Skin and hair

Question 4

Which of the following is NOT a dimorphic fungus?

Accepted Answer

Phialophora

Answer

Blastomyces dermatitidis

Answer

Histoplasma

Answer

Penicillium marneffei

Question 5

Rhinosporidium seeberi is classified as which type of organism?

Accepted Answer

Mesomycetozoa

Answer

Fungi

Answer

Bacteria

Answer

Protozoa

Question 6

Pseudohyphae are seen in which of the following fungi?

Accepted Answer

Candida

Answer

Cryptococcus

Answer

Rhizopus

Answer

Mucor

Question 7

Tinea capitis is caused by which of the following fungi, except?

Accepted Answer

Epidermophyton

Answer

Microsporum

Answer

Trichophyton violaceum

Answer

Trichophyton schoenleinii

Question 8

Which of the following are characteristic features or predisposing factors of Mucormycosis?

Accepted Answer

Lymph invasion

Answer

Angio-invasion

Answer

Septate hyphae

Answer

Long-term deferoxamine therapy is a predisposing factor

Question 9

Spindle-shaped conidia are characteristic of which fungus?

Accepted Answer

Fusarium

Answer

Aspergillus

Answer

Penicillium

Answer

Conidiobolus

Question 10

Some fungi exhibit dimorphism, presenting in two distinct morphological forms: yeast and mold. If a fungus is dimorphic, which of the following is the most likely scenario regarding its morphological forms?

Accepted Answer

The mold form is found in the environment, and the yeast form is found in human tissues.

Answer

The yeast form is found in the environment, and the mold form is found in human tissues.

Answer

Both the yeast and mold forms are typically found in human tissues.

Answer

Neither form appears in tissue, as these organisms are nonpathogenic.

Mycology — MCQs

Mycology — MCQs

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