Mycology Practice Questions

Q: Clavate macroconidia are characteristic of which one of the following fungi?

E. floccosum. **Explanation:** The correct answer is **A. *Epidermophyton floccosum***. In medical mycology, the morphology of macroconidia is a high-yield diagnostic feature used to differentiate dermatophytes. *Epidermophyton floccosum* is characterized by **clavate (club-shaped)**, smooth-walled macroconidia that typically contain 2–4 cells. These are often found in clusters (bunches of bananas) and, notably, this genus **lacks microconidia**, which is a key identifying trait. **Analysis of Incorrect Options:** * **B. *Coccidioides immitis*:** This is a dimorphic fungus. Its characteristic feature in culture is the formation of **barrel-shaped arthroconidia** with alternating empty cells (disjunctor cells), not clavate macroconidia. * **C. *Phialophora verrucosa*:** This is a causative agent of chromoblastomycosis. It produces characteristic **flask-shaped phialides** with a distinct collarette, from which oval conidia emerge. * **D. *Microsporum canis*:** This fungus produces **spindle-shaped (fusiform)** macroconidia that are thick-walled, multi-septate (usually >6 cells), and often have a curved or hooked apex. **NEET-PG High-Yield Pearls:** * **Dermatophyte Differentiation:** * *Microsporum*: Spindle-shaped macroconidia; infects hair and skin. * *Trichophyton*: Pencil-shaped/Cylindrical macroconidia (rare); infects hair, skin, and nails. * *Epidermophyton*: Club-shaped (Clavate) macroconidia; infects **skin and nails only** (never hair). * **Clinical Presentation:** *E. floccosum* is a common cause of Tinea cruris and Tinea pedis. * **Culture:** On Sabouraud Dextrose Agar (SDA), *E. floccosum* produces greenish-yellow, suede-like colonies.

Q: A normally healthy 9-year-old boy presents with a 4-day history of fever, cough, and lower respiratory symptoms, with no upper respiratory tract symptoms. His chest sounds are consistent with pneumonia, and a chest radiograph shows small, patchy infiltrates with hilar adenopathy. A blood smear reveals small, nondescript yeast forms within monocytic cells. What is the most likely causative agent?

Histoplasma capsulatum. ### Explanation **Correct Answer: B. Histoplasma capsulatum** The clinical presentation and laboratory findings are classic for **Histoplasmosis**. *Histoplasma capsulatum* is a dimorphic fungus that exists as a mold in the environment (soil enriched with bird or bat droppings) and as a yeast in the human body. The key diagnostic clue in this question is the presence of **small yeast forms within monocytic cells (macrophages)**. Histoplasma is an intracellular pathogen; once inhaled, it is phagocytosed by alveolar macrophages, where it survives and replicates. The radiographic findings of patchy infiltrates and **hilar adenopathy** are typical for primary pulmonary histoplasmosis, which often mimics tuberculosis or sarcoidosis. **Why other options are incorrect:** * **A. Sporotrichosis:** Caused by *Sporothrix schenckii*, it typically presents as "rose gardener’s disease" with subcutaneous nodules following a linear lymphatic distribution. It rarely causes pneumonia in immunocompetent children. * **C. Coccidioides immitis:** While it causes pulmonary symptoms, the characteristic tissue form is a **spherule containing endospores**, not small yeasts within macrophages. * **D. Pneumocystis jiroveci:** This is an opportunistic pathogen seen primarily in immunocompromised patients (e.g., HIV). It presents with interstitial "ground-glass" opacities and is identified by silver-stained cysts, not intracellular yeasts in monocytes. **NEET-PG High-Yield Pearls:** * **Mnemonic for Histoplasma:** "**H**isto **H**ides in **H**istiocytes" (Macrophages). * **Geography:** Associated with Ohio and Mississippi River Valleys (USA), but also found in parts of India (e.g., Gangetic plains). * **Diagnosis:** Best visualized using **Gomori Methenamine Silver (GMS)** or PAS stain. * **Clinical Mimic:** It is a common cause of granulomatous inflammation and can mimic Tuberculosis (calcified lung nodules/Ghon complexes).

Q: The hair perforation test is positive in infections caused by which of the following fungi?

Trichophyton. **Explanation:** The **Hair Perforation Test** (In-vitro hair perforation test) is a diagnostic laboratory procedure used to differentiate between various dermatophytes based on their ability to produce specialized wedge-shaped enzymatic erosions (perforations) in human hair shafts. **1. Why Trichophyton is correct:** The test is primarily used to distinguish **Trichophyton mentagrophytes** (Positive) from **Trichophyton rubrum** (Negative). *T. mentagrophytes* produces keratinolytic enzymes that allow the hyphae to penetrate the hair cuticle and cortex perpendicularly, creating distinct pits or perforations. While not all *Trichophyton* species are positive, the genus is the classic association for this test in competitive exams. **2. Why the other options are incorrect:** * **Exophiala werneckii:** This is the causative agent of *Tinea nigra* (a superficial mycosis). It involves the skin (palms/soles) but does not invade hair or produce the specific keratinases required for hair perforation. * **Epidermophyton:** This genus (specifically *E. floccosum*) is known for infecting skin and nails but **never infects hair**. Therefore, it cannot be tested via hair perforation. **High-Yield Clinical Pearls for NEET-PG:** * **Positive Test:** *Trichophyton mentagrophytes*, *Microsporum canis*. * **Negative Test:** *Trichophyton rubrum*, *Microsporum audouinii*. * **Memory Aid:** *T. **m**entagrophytes* is **M**ighty (perforates), while *T. **r**ubrum* is **R**eluctant (does not). * **Procedure:** Sterilized human hair is incubated with the fungus in water supplemented with yeast extract for up to 4 weeks. Perforations are visualized using Lactophenol Cotton Blue (LPCB) stain.

Q: A deficiency of which of the following cells can predispose to candidiasis?

T Lymphocytes. **Explanation:** The correct answer is **T Lymphocytes**. The body’s defense against *Candida albicans* is a dual mechanism involving both innate and adaptive immunity. 1. **Why T Lymphocytes are correct:** Cell-Mediated Immunity (CMI), specifically **Th17 and Th1 cells**, is crucial for controlling mucocutaneous fungal infections. T lymphocytes produce cytokines (like IL-17 and IL-22) that recruit neutrophils and maintain mucosal integrity. A deficiency in T-cells (as seen in HIV/AIDS or Chronic Mucocutaneous Candidiasis) leads to persistent **mucocutaneous candidiasis** (oral thrush, esophagitis). 2. **Why other options are incorrect:** * **Eosinophils:** These are primarily involved in defense against helminthic (parasitic) infections and type I hypersensitivity reactions; they play a negligible role in fungal defense. * **Macrophages:** While they act as antigen-presenting cells and can ingest yeast, they are not the primary cell type whose *deficiency* characteristically predisposes to candidiasis compared to T-cells or neutrophils. * **Plasma cells:** These produce antibodies (Humoral Immunity). While antibodies can prevent systemic spread, they are not the primary defense against the localized mucosal colonization of *Candida*. **Clinical Pearls for NEET-PG:** * **Dual Defense Rule:** * **T-cell deficiency** predisposes to **Mucocutaneous Candidiasis** (e.g., HIV patients). * **Neutrophil deficiency** (Neutropenia) predisposes to **Disseminated/Systemic Candidiasis** (e.g., chemotherapy patients). * **Th17 cells** are the specific subset of T-cells most vital for fungal immunity at mucosal surfaces. * **Chronic Mucocutaneous Candidiasis (CMC)** is often associated with AIRE gene mutations or STAT1 signaling defects.

Q: An HIV-infected patient presents with oral lesions. What is the most likely causative organism?

Candida. **Explanation:** **Why Candida is the correct answer:** Oropharyngeal Candidiasis (Oral Thrush) is the **most common opportunistic infection** in HIV-infected individuals. It typically occurs when the CD4 count falls below **200-500 cells/mm³**. Clinically, it presents as creamy white, curd-like patches on the tongue or buccal mucosa that can be scraped off, leaving an erythematous base. It is often the first clinical sign of HIV progression. **Analysis of Incorrect Options:** * **A. Epstein-Barr virus (EBV):** While EBV causes **Oral Hairy Leukoplakia** in HIV patients (white, corrugated lesions on the lateral borders of the tongue), it is less common than Candidiasis. Crucially, these lesions *cannot* be scraped off. * **C. Cytomegalovirus (CMV):** CMV typically causes painful, deep **oral ulcers** or esophagitis in severely immunocompromised patients (CD4 < 50 cells/mm³), but it is not the most frequent cause of oral lesions. * **D. Pneumocystis carinii (jirovecii):** This is the most common opportunistic *respiratory* infection (Pneumonia) in HIV patients. While it can rarely present extrapulmonary, it is not a primary cause of oral lesions. **High-Yield Clinical Pearls for NEET-PG:** * **Most common oral manifestation of HIV:** Candidiasis. * **Treatment of choice:** Topical Nystatin or Clotrimazole for mild cases; Oral Fluconazole for moderate to severe cases. * **Oral Hairy Leukoplakia (EBV):** A key diagnostic marker for HIV progression; does not require specific treatment unless symptomatic. * **Kaposi Sarcoma (HHV-8):** Presents as painless, purple/red nodules on the hard palate; it is the most common oral malignancy in HIV.

Q: All of the following are true regarding Cryptococcus neoformans except?

Anticapsular antibody is protective. **Explanation:** *Cryptococcus neoformans* is an encapsulated yeast that primarily causes meningitis. The key to understanding this question lies in the host's immune response to the fungus. **Why Option D is the correct answer (False statement):** In Cryptococcosis, the **cell-mediated immunity (CMI)**—specifically T-cells and macrophages—is the primary defense mechanism. While the body does produce antibodies against the polysaccharide capsule, these **anticapsular antibodies are NOT protective**. They do not aid in clearing the infection, which is why patients with impaired CMI (like those with HIV/AIDS) are highly susceptible regardless of antibody levels. **Analysis of Incorrect Options (True statements):** * **Option A:** It is a classic **opportunistic pathogen**. While it can affect healthy individuals, it most severely affects immunocompromised patients, particularly those with CD4 counts <100 cells/µL. * **Option B:** Like most fungi, *Cryptococcus* grows well on **Sabouraud’s Dextrose Agar (SDA)**, appearing as mucoid, cream-colored colonies. It also grows on Bird Seed Agar (Niger seed agar), producing melanin. * **Option C:** Detection of the **capsular polysaccharide antigen (CrAg)** via Latex Agglutination or Lateral Flow Assay (LFA) in the CSF or serum is a highly sensitive and specific diagnostic gold standard. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Spherical budding yeast with a wide polysaccharide capsule (demonstrated by **India Ink** as a clear halo). * **Virulence Factor:** The capsule is the most important; **Phenoloxidase enzyme** (melanin production) is another. * **Source:** Pigeon droppings and soil. * **Stains:** Mucicarmine (stains capsule red), Fontana-Masson (stains melanin). * **Treatment:** Induction with Amphotericin B + Flucytosine, followed by Fluconazole.

Q: Candidiasis is a complication of all of the following except?

Aspiration pneumonia. **Explanation:** The correct answer is **Aspiration pneumonia**. **1. Why Aspiration Pneumonia is the Correct Answer:** Aspiration pneumonia is typically caused by the inhalation of oropharyngeal or gastric contents into the lower respiratory tract. The primary pathogens involved are **anaerobic bacteria** (e.g., *Bacteroides*, *Fusobacterium*) and aerobic bacteria (e.g., *S. pneumoniae*, *K. pneumoniae*). Candidiasis is not a recognized complication of aspiration pneumonia because the pathophysiology involves chemical irritation and bacterial infection rather than fungal overgrowth. **2. Analysis of Incorrect Options:** * **Prolonged Antibiotic Therapy:** Broad-spectrum antibiotics suppress the normal bacterial flora (e.g., *Lactobacillus*), which usually keeps *Candida* in check. This loss of competition leads to fungal overgrowth, causing oral thrush or vaginal candidiasis. * **Corticosteroid Therapy:** Steroids are immunosuppressive. They inhibit T-cell function and neutrophil activity, reducing the body's ability to fight opportunistic infections like *Candida*. * **Immunocompromised Disease:** Conditions like HIV/AIDS (where CD4 counts drop), diabetes mellitus, and neutropenia are classic risk factors. *Candida* is an opportunistic pathogen that thrives when the host's cellular immunity is impaired. **3. High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** *Candida albicans* is unique because it shows **pseudohyphae** at 37°C and **Germ tubes** (Reynolds-Braude phenomenon) when incubated in serum at 37°C for 2 hours. * **Culture:** Grows on **Sabouraud Dextrose Agar (SDA)** as creamy white, smooth colonies with a "yeasty" odor. * **Chronic Mucocutaneous Candidiasis (CMC):** Associated with T-cell defects and endocrine abnormalities. * **Drug of Choice:** Fluconazole for superficial infections; Echinocandins (e.g., Caspofungin) or Amphotericin B for systemic/invasive candidiasis.

Q: Histoplasma capsulatum is a:

Dimorphic fungus. **Explanation:** *Histoplasma capsulatum* is the causative agent of Histoplasmosis (Darling’s disease). The correct answer is **Dimorphic fungus** because it exhibits two distinct morphological forms depending on the environmental temperature: 1. **At 25°C (Saprophytic phase):** It grows as a mold with hyphae, producing characteristic large, thick-walled, spiked **tuberculate macroconidia**. 2. **At 37°C (Parasitic phase):** It grows as small, oval budding yeast cells within the host’s macrophages. **Analysis of Incorrect Options:** * **A. Protozoa:** Despite its name and its intracellular nature (resembling *Leishmania*), it is a fungus, not a parasite. * **C. Amphotericin resistant:** This is incorrect. Amphotericin B is the gold standard treatment for severe or disseminated Histoplasmosis. * **D. Capsulated:** This is a **classic distractor**. Despite the name *capsulatum*, this fungus is **not** encapsulated. The "halo" seen around the yeast cells in tissue sections is actually a staining artifact caused by the shrinkage of the cytoplasm away from the cell wall. **High-Yield Clinical Pearls for NEET-PG:** * **Habitat:** Found in soil enriched with **bird or bat droppings** (guano); common among cave explorers (Spelunker’s lung). * **Pathogenesis:** It is an **intracellular** pathogen that survives inside **macrophages**. * **Clinical Presentation:** Can mimic Tuberculosis (hilar lymphadenopathy and lung calcifications). * **Diagnosis:** Best diagnosed via fungal culture (SDA) or by observing intracellular yeasts in peripheral blood smears or bone marrow aspirates.

Question 1

Clavate macroconidia are characteristic of which one of the following fungi?

Accepted Answer

E. floccosum

Answer

C. immitis

Answer

P. verrucosa

Answer

M. canis

Question 2

A normally healthy 9-year-old boy presents with a 4-day history of fever, cough, and lower respiratory symptoms, with no upper respiratory tract symptoms. His chest sounds are consistent with pneumonia, and a chest radiograph shows small, patchy infiltrates with hilar adenopathy. A blood smear reveals small, nondescript yeast forms within monocytic cells. What is the most likely causative agent?

Accepted Answer

Histoplasma capsulatum

Answer

Sporotrichosis

Answer

Coccidioides immitis

Answer

Pneumocystis jiroveci

Question 3

The hair perforation test is positive in infections caused by which of the following fungi?

Accepted Answer

Trichophyton

Answer

Exophila werneckii

Answer

Epidermophyton

Answer

All of the above

Question 4

A deficiency of which of the following cells can predispose to candidiasis?

Accepted Answer

T Lymphocytes

Answer

Eosinophils

Answer

Macrophages

Answer

Plasma cells

Question 5

A HIV-positive female presents with an indurated ulcer over the tongue. Laboratory findings show growth in cornmeal agar at 20°C, microscopy showing hyphae, and growth in human serum at 37°C showing budding yeasts. What is the probable causative agent?

Accepted Answer

Candida albicans

Answer

Histoplasmosis

Answer

Blastomycosis

Answer

Coccidioidomycosis

Question 6

An HIV-infected patient presents with oral lesions. What is the most likely causative organism?

Accepted Answer

Candida

Answer

Epstein-Barr virus (EBV)

Answer

Cytomegalovirus (CMV)

Answer

Pneumocystis carinii

Question 7

All of the following are true regarding Cryptococcus neoformans except?

Accepted Answer

Anticapsular antibody is protective

Answer

Affects immunocompromised patients

Answer

Grown on Sabouraud's agar

Answer

Capsular antigen can be detected in the CSF

Question 8

Candidiasis is a complication of all of the following except?

Accepted Answer

Aspiration pneumonia

Answer

Prolonged antibiotic therapy

Answer

Corticosteroid therapy

Answer

Immunocompromised disease

Question 9

Histoplasma capsulatum is a:

Accepted Answer

Dimorphic fungus

Answer

Protozoa

Answer

Amphotericin resistant

Answer

Capsulated

Question 10

All of the following statements regarding fungi are true EXCEPT:

Accepted Answer

Dimorphic fungi behave as molds in cultures incubated at 37°C.

Answer

Yeasts are unicellular fungi.

Answer

Candida species can form pseudomycelia.

Answer

Dermatophytes are typically filamentous fungi.

Mycology — MCQs

Mycology — MCQs

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