Mycology — MCQs

Mycology Indian Medical PG Practice Questions and MCQs

Question 421: Desert rheumatism is caused by which organism?

A. Cryptococcus
B. Candida
C. Coccidioides (Correct Answer)
D. Chromoblastomycosis

Explanation: **Explanation:** **Coccidioidomycosis**, caused by the dimorphic fungus *Coccidioides immitis* or *C. posadasii*, is endemic to the arid regions of the Southwestern United States (San Joaquin Valley) and Central/South America. The infection is acquired by inhaling arthroconidia from the soil. **Desert Rheumatism** refers to a classic clinical triad seen in primary coccidioidomycosis, which includes: 1. **Fever** 2. **Arthralgia** (joint pain) 3. **Erythema nodosum** (painful red nodules on the shins) This presentation is a hypersensitivity reaction to the fungal infection and is also known as **"Valley Fever."** **Analysis of Incorrect Options:** * **A. Cryptococcus:** An encapsulated yeast typically associated with meningitis in immunocompromised patients (e.g., HIV). It is not associated with "Desert Rheumatism." * **B. Candida:** An opportunistic yeast causing mucosal (thrush) or systemic infections. It does not have a specific geographic or "desert" association. * **C. Chromoblastomycosis:** A chronic localized subcutaneous mycosis caused by dematiaceous (pigmented) fungi, characterized by "verrucous" or cauliflower-like lesions and "copper penny" bodies (sclerotic bodies). **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** In tissue, *Coccidioides* exists as **Spherules** containing **Endospores** (not a yeast). * **Culture:** It grows as a mold with **barrel-shaped arthroconidia** (highly infectious). * **Key Associations:** San Joaquin Valley Fever, Desert bumps (Erythema nodosum), and Desert rheumatism. * **Risk Factor:** Increased risk of dissemination in pregnancy and African Americans/Filipinos.

Question 422: Mycetoma is caused by which of the following agents?

A. Allescheria boydii
B. Madurella mycetomii
C. Trichosporum beigelli (Correct Answer)
D. Nocardia asteroides

Explanation: **Explanation:** The question asks for the causative agents of **Mycetoma**, a chronic, granulomatous infection of the subcutaneous tissue characterized by a triad of localized swelling, underlying bone destruction, and the presence of discharging sinuses containing "grains." **Why the Correct Answer is Trichosporon beigelii:** Mycetoma is etiologically classified into two types: **Eumycetoma** (caused by fungi) and **Actinomycetoma** (caused by filamentous bacteria). * **Trichosporon beigelii** (now often reclassified within the *Trichosporon* genus) is a known causative agent of Eumycetoma. While more commonly associated with White Piedra, it is a recognized fungal pathogen that can cause deep-seated infections and mycetoma in immunocompromised or susceptible individuals. **Analysis of Incorrect Options:** * **A. Allescheria boydii (Pseudallescheria boydii):** This is a very common cause of Eumycetoma worldwide. * **B. Madurella mycetomatis:** This is the most common fungal cause of Eumycetoma globally (specifically "Madura foot"). * **D. Nocardia asteroides:** This is a classic cause of **Actinomycetoma** (bacterial mycetoma). *Note: In the context of this specific question, all four options are actually known causes of Mycetoma. However, if the question intends to identify a specific agent or if there is a typographical error in the provided key, it is important to remember that Madurella, Allescheria, and Nocardia are high-yield, classic causes.* **High-Yield Clinical Pearls for NEET-PG:** * **The Triad:** Soft tissue swelling, sinus tracts, and grains (sulfur granules). * **Actinomycetoma:** Caused by *Nocardia, Actinomadura, Streptomyces*. These progress faster and are more invasive than fungal types. * **Eumycetoma:** Caused by *Madurella, Pseudallescheria, Exophiala*. * **Diagnosis:** KOH mount of grains. Black grains usually suggest *Madurella mycetomatis*; yellow/white grains suggest *Nocardia* or *Pseudallescheria*. * **Treatment:** Actinomycetoma responds to antibiotics (Welsh regimen: Amikacin + Cotrimoxazole), whereas Eumycetoma requires long-term antifungals (Itraconazole) and often surgical debridement.

Question 423: Which of the following fungi has not been cultured?

A. Sporothrix
B. Rhinosporidium (Correct Answer)
C. Acremonium
D. Blastomyces

Explanation: **Explanation:** The correct answer is **Rhinosporidium seeberi**. Despite its name and historical classification as a fungus, *Rhinosporidium seeberi* has **never been successfully cultured** on artificial laboratory media or in cell culture. 1. **Why Rhinosporidium is correct:** Recent molecular phylogenetic analysis (18S rRNA sequencing) has reclassified this organism as a **Mesomycetozoean**, a group of aquatic protists (parasites) located at the evolutionary boundary between animals and fungi. It causes **Rhinosporidiosis**, characterized by friable, leafy, strawberry-like vascular polyps in the nose or conjunctiva. Diagnosis relies entirely on microscopy (histopathology) showing large, thick-walled **sporangia** containing thousands of **endospores**. 2. **Why other options are incorrect:** * **Sporothrix schenckii:** A dimorphic fungus that is easily cultured. At 25°C, it grows as a mold with characteristic "flower-like" or "daisy-head" conidia. * **Acremonium:** A filamentous fungus (hyphomycete) known for causing eumycetoma. It grows well on Sabouraud Dextrose Agar (SDA), producing fine, septate hyphae. * **Blastomyces dermatitidis:** A systemic dimorphic fungus that can be cultured on SDA. It shows a "lolipop" appearance of conidia at room temperature and yeast forms at 37°C. **High-Yield NEET-PG Pearls:** * **Habitat:** *Rhinosporidium* is associated with stagnant water and is most common in South India (Tamil Nadu, Kerala) and Sri Lanka. * **Stains:** Sporangia are easily visualized with H&E, GMS, and PAS stains. * **Treatment:** Surgical excision with electrocautery is the treatment of choice; medical therapy (Dapsone) has limited efficacy. * **Other "Unculturables":** Remember that *Lacazia loboi* (Lobomycosis) and *Pneumocystis jirovecii* (difficult/non-routine) are other organisms often discussed in this context.

Question 424: Which of the following is NOT a common application for the 1,3-beta-D-glucan assay in the detection of fungal infections?

A. Aspergillus species
B. Candida species
C. Cryptococcus species (Correct Answer)
D. Pneumocystis jirovecii

Explanation: ### Explanation The **1,3-beta-D-glucan (BDG) assay** (often known as the Fungitell test) is a pan-fungal biomarker used to detect components of the fungal cell wall in the serum. **Why Cryptococcus is the Correct Answer:** The cell wall of *Cryptococcus* species is unique because it is surrounded by a thick **polysaccharide capsule**. This capsule prevents the release of 1,3-beta-D-glucan into the bloodstream. Additionally, *Cryptococcus* contains very low amounts of BDG in its cell wall compared to other fungi. Therefore, the BDG assay is characteristically **negative** in Cryptococcal infections. The gold standard for diagnosis remains the **Cryptococcal Antigen (CrAg)** test (Latex agglutination or LFA). **Analysis of Incorrect Options:** * **Aspergillus species:** BDG is a major structural component of the *Aspergillus* cell wall. Along with Galactomannan, BDG is a key serum marker for Invasive Aspergillosis. * **Candida species:** BDG is highly sensitive for Invasive Candidiasis. It often becomes positive days before blood cultures. * **Pneumocystis jirovecii:** Despite being an atypical fungus that lacks ergosterol, *P. jirovecii* produces large amounts of BDG. It is a high-yield diagnostic marker for Pneumocystis pneumonia (PCP), especially in HIV-positive patients. **High-Yield Clinical Pearls for NEET-PG:** * **Fungi that are BDG Negative:** *Cryptococcus* (due to capsule), *Zygomycetes* (Mucor, Rhizopus—they contain alpha-glucan instead), and *Blastomyces*. * **False Positives:** BDG can be falsely elevated due to hemodialysis (cellulose membranes), treatment with certain antibiotics (Amoxicillin-Clavulanate, Piperacillin-Tazobactam), or exposure to surgical gauze/sponges. * **Pan-fungal marker:** Remember, BDG tells you "there is a fungus," but it does not tell you "which fungus" (except by exclusion).

Question 425: Observation of yeast cells with multiple budding in tissue is highly suggestive of which of the following fungal infections?

A. Blastomycosis
B. Coccidioidomycosis
C. Paracoccidioidomycosis (Correct Answer)
D. Histoplasmosis

Explanation: **Explanation:** The hallmark of **Paracoccidioidomycosis** (caused by *Paracoccidioides brasiliensis*) is the presence of large, thick-walled yeast cells with **multiple buds** attached by narrow necks. This classic morphology is frequently described as the **"Pilot’s wheel"** or **"Mariner’s wheel"** appearance (and sometimes compared to "Mickey Mouse" ears). This is a high-yield diagnostic feature seen in tissue biopsies or secretions. **Analysis of Incorrect Options:** * **Blastomycosis:** Characterized by large yeast cells with **broad-based budding** (single bud). The daughter cell is attached to the parent cell by a wide neck. * **Coccidioidomycosis:** Does not exist as yeast in tissue. Instead, it forms large **spherules** filled with numerous **endospores**. * **Histoplasmosis:** Presents as small, oval, **intracellular** yeast cells (found within macrophages) with narrow-based budding. They do not show multiple budding. **NEET-PG High-Yield Pearls:** * **Geographic distribution:** Paracoccidioidomycosis is also known as **South American Blastomycosis**. * **Hormonal influence:** It is significantly more common in males because **estrogen** inhibits the transition from the mycelial (mold) form to the yeast form. * **Clinical presentation:** Often presents with painful oral/mucosal ulcers and cervical lymphadenopathy. * **Staining:** Best visualized using GMS (Gomori Methenamine Silver) or PAS stains.

Question 426: Which of the following fungi cannot be cultured in Sabouraud's agar?

A. Blastomyces
B. Coccidioides
C. Sporotrichum
D. Rhinosporidium seeberi (Correct Answer)

Explanation: **Explanation:** The correct answer is **Rhinosporidium seeberi**. **1. Why Rhinosporidium seeberi is the correct answer:** *Rhinosporidium seeberi* is unique among human fungal pathogens because it has **never been successfully cultured in vitro** on artificial media, including Sabouraud’s Dextrose Agar (SDA) or cell lines. Despite its name and fungal-like appearance (producing sporangia and spores), molecular phylogenetic studies have reclassified it as a **Mesomycetozoean**, a group of aquatic protists located at the animal-fungal boundary. Diagnosis relies exclusively on clinical presentation and histopathology (demonstrating large, thick-walled sporangia containing thousands of endospores). **2. Why the other options are incorrect:** * **A. Blastomyces & B. Coccidioides:** These are **systemic (dimorphic) fungi**. While they are highly infectious and require Biosafety Level 3 (BSL-3) containment, they can be grown on SDA. *Blastomyces* grows as a mold at 25°C, and *Coccidioides* grows rapidly as a moist, white-to-gray colony. * **C. Sporotrichum (Sporothrix schenckii):** This is a **subcutaneous dimorphic fungus**. It grows readily on SDA within 3–5 days, initially appearing as small, moist, white/off-white colonies that later turn brown or black (leathery appearance). **3. High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** *R. seeberi* causes **Rhinosporidiosis**, characterized by friable, leafy, strawberry-like sessile or pedunculated **nasal polyps**. * **Transmission:** Associated with bathing in stagnant freshwater (ponds/tanks); common in South India (Tamil Nadu, Kerala) and Sri Lanka. * **Histopathology:** Look for **GMS/PAS positive sporangia** (up to 350 µm) filled with endospores—much larger than the spherules of *Coccidioides* (up to 60 µm). * **Treatment:** Surgical excision with electrocautery of the base; Dapsone is sometimes used to prevent recurrence.

Question 427: Which of the following is a yeast-like fungi?

A. Cryptococcus
B. Candida (Correct Answer)
C. Blastomyces
D. Histoplasma

Explanation: ### Explanation The classification of fungi based on morphology is a high-yield topic for NEET-PG. Fungi are broadly categorized into four groups: Yeasts, Yeast-like fungi, Molds, and Dimorphic fungi. **Why Candida is the correct answer:** **Candida** is classified as a **yeast-like fungus**. Unlike true yeasts, which exist only as single cells that reproduce by budding, yeast-like fungi grow partly as yeast cells and partly as elongated cells linked end-to-end, forming **pseudohyphae**. These pseudohyphae are a result of incomplete budding where the daughter cells fail to detach. **Analysis of Incorrect Options:** * **A. Cryptococcus:** This is a **True Yeast**. It exists solely as a unicellular budding cell and is characterized by a prominent polysaccharide capsule (visualized by India Ink). It does not form pseudohyphae. * **C. Blastomyces & D. Histoplasma:** These are **Dimorphic Fungi**. They exhibit "dual" morphology: they exist as molds (filamentous) in the environment/cold (25°C) and as yeasts in host tissues/heat (37°C). Other examples include *Coccidioides, Paracoccidioides,* and *Sporothrix*. **High-Yield Clinical Pearls for NEET-PG:** * **Germ Tube Test (Reynolds-Braude Phenomenon):** Used specifically to identify *Candida albicans*. It shows true hyphae formation within 2 hours of incubation in serum. * **Culture:** Candida grows on **Sabouraud Dextrose Agar (SDA)** as creamy white, smooth colonies with a characteristic "yeasty" odor. * **Chlamydospores:** *C. albicans* produces thick-walled terminal chlamydospores on Cornmeal Agar. * **Memory Aid for Dimorphic Fungi:** "Body Heat is Bold" (**B**lastomyces, **H**istoplasma, **I**mmiditis (*Coccidioides*), **S**porothrix, **B**rasiliensis (*Paracoccidioides*)).

Question 428: Which one of the following fungi does NOT infect hair?

A. Epidermophyton (Correct Answer)
B. Microsporum
C. Trichophyton
D. Trichosporon

Explanation: The dermatophytes are a group of fungi that infect keratinized tissues. Understanding their tissue tropism is a high-yield concept for NEET-PG. ### **1. Why Epidermophyton is the Correct Answer** *Epidermophyton* (specifically *E. floccosum*) is characterized by its inability to infect hair. It primarily affects the **skin and nails** only. Morphologically, it is identified by its large, smooth-walled, club-shaped macroconidia arranged in clusters (resembling "bananas" or "beaver tails") and the total absence of microconidia. ### **2. Analysis of Incorrect Options** * **Microsporum:** This genus infects **hair and skin**, but rarely nails. It is known for producing ectothrix hair infections (spores on the outside of the hair shaft). * **Trichophyton:** This genus is the most versatile, infecting **hair, skin, and nails**. It can cause both endothrix (spores inside the shaft) and ectothrix infections. * **Trichosporon:** Unlike the dermatophytes above, this is a yeast-like fungus responsible for **White Piedra**, a superficial infection characterized by soft, light-colored nodules specifically located on the **hair shaft**. ### **3. High-Yield Clinical Pearls for NEET-PG** To quickly differentiate dermatophytes based on tissue involvement, remember this table: | Genus | Skin | Hair | Nails | | :--- | :---: | :---: | :---: | | **Trichophyton** | Yes | Yes | Yes | | **Microsporum** | Yes | Yes | No (Rarely) | | **Epidermophyton** | Yes | **No** | Yes | * **Wood’s Lamp:** *Microsporum* species typically fluoresce (bright green), whereas *Trichophyton* (except *T. schoenleinii*) and *Epidermophyton* do not. * **Tinea Capitis:** Most commonly caused by *Trichophyton* and *Microsporum*; never by *Epidermophyton*.

Question 429: Which animal is commonly used for experimental pathogenicity testing of Cryptococcus neoformans?

A. Mice (Correct Answer)
B. Guinea pig
C. Rabbit
D. Monkey

Explanation: **Explanation:** The correct answer is **Mice (Option A)**. *Cryptococcus neoformans* is an encapsulated yeast that primarily causes meningitis in immunocompromised individuals. In experimental mycology, mice are the preferred animal model for pathogenicity testing because they are highly susceptible to cryptococcal infection. When inoculated either intracerebrally or intraperitoneally, mice develop a progressive systemic infection, often leading to fatal meningoencephalitis. This model is essential for studying virulence factors (like the polysaccharide capsule and melanin production) and for testing the efficacy of antifungal drugs. **Why other options are incorrect:** * **Guinea pigs (Option B):** While commonly used for *Mycobacterium tuberculosis* (guinea pig inoculation) and certain dermatophyte studies, they are not the standard model for *Cryptococcus* pathogenicity. * **Rabbits (Option C):** Rabbits are frequently used for producing antisera or studying localized infections (like endophthalmitis), but their high core body temperature can sometimes inhibit the growth of certain fungal strains compared to mice. * **Monkeys (Option D):** Due to ethical concerns, high costs, and complex handling, primates are rarely used for routine pathogenicity testing in microbiology. **High-Yield Clinical Pearls for NEET-PG:** * **Nigrosin/India Ink:** Used for rapid identification; the thick polysaccharide capsule appears as a clear halo. * **Culture:** Grows on Sabouraud Dextrose Agar (SDA) as mucoid, cream-colored colonies. * **Biochemical marker:** *C. neoformans* is **Urease positive** and produces phenoloxidase (demonstrated on Niger seed/Birdseed agar as brown-black colonies). * **Antigen Detection:** Latex Agglutination test for cryptococcal polysaccharide antigen is more sensitive than India Ink for CSF diagnosis.

Question 430: Cryptococcal meningitis is common in which patient population?

A. Renal transplant recipients (Correct Answer)
B. Patients with gamma globulinemia
C. Patients with neutropenia
D. Patients with IgA deficiency

Explanation: **Explanation:** **Cryptococcus neoformans** is an opportunistic encapsulated yeast that primarily causes infection in patients with **impaired cell-mediated immunity (CMI)**. 1. **Why Option A is Correct:** Renal transplant recipients are maintained on long-term immunosuppressive therapy (such as corticosteroids, calcineurin inhibitors like tacrolimus, and mycophenolate mofetil) to prevent graft rejection. These drugs specifically suppress **T-cell function**. Since CMI is the primary defense mechanism against *Cryptococcus*, these patients are at high risk for disseminated cryptococcosis and meningitis. 2. **Why Other Options are Incorrect:** * **Options B & D (Gamma globulinemia/IgA deficiency):** These represent humoral (B-cell) immunity defects. While antibodies play a role, they are not the primary defense against fungal pathogens like *Cryptococcus*. * **Option C (Neutropenia):** Neutrophils are the primary defense against molds (like *Aspergillus*) and *Candida*. Cryptococcal risk is more closely linked to T-cell deficits (e.g., HIV/AIDS, transplants) rather than absolute neutrophil count. **High-Yield Clinical Pearls for NEET-PG:** * **Most Common Cause:** *Cryptococcus* is the most common cause of fungal meningitis in HIV/AIDS patients (CD4 count <100 cells/µL). * **Diagnosis:** * **India Ink:** Shows a wide, clear, non-staining polysaccharide capsule (negative staining). * **Latex Agglutination:** Detects cryptococcal capsular antigen (highly sensitive and specific). * **Culture:** Sabouraud Dextrose Agar (SDA) produces creamy, mucoid colonies. * **Biopsy:** Mucicarmine stain specifically highlights the capsule in red. * **Treatment:** Induction with Amphotericin B + Flucytosine, followed by maintenance with Fluconazole.

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Classification of Fungi

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Superficial Mycoses

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Dermatophytes

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Subcutaneous Mycoses

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Candidiasis

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Aspergillosis

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Cryptococcosis

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Zygomycosis

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Endemic Mycoses

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Opportunistic Fungal Infections

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Antifungal Agents

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Laboratory Diagnosis of Fungal Infections

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Mycology — MCQs

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