Mycology Practice Questions

Q: What is the most common organism causing meningitis in a patient with AIDS?

Cryptococcus neoformans. **Explanation:** **Cryptococcus neoformans** is the most common cause of fungal meningitis and the overall most common cause of meningitis in patients with AIDS, typically occurring when the **CD4 count falls below 100 cells/mm³**. It is an opportunistic encapsulated yeast acquired through inhalation of pigeon droppings. The organism exhibits neurotropism, spreading hematogenously to the meninges, leading to subacute or chronic meningitis characterized by high intracranial pressure. **Analysis of Incorrect Options:** * **Candida albicans:** While a common opportunistic infection in AIDS (causing oral thrush or esophagitis), it rarely causes meningitis. When it does, it is usually associated with neurosurgical procedures or disseminated candidiasis in neutropenic patients. * **Streptococcus pneumoniae:** This is the most common cause of community-acquired bacterial meningitis in the general population. While HIV patients are at a higher risk for pneumococcal infections, *Cryptococcus* remains more frequent in the advanced stages of AIDS. * **Haemophilus influenzae:** Since the introduction of the Hib vaccine, the incidence of this meningitis has significantly decreased. It is more common in unvaccinated children than in adult AIDS patients. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnosis:** **India Ink preparation** shows a "halo" (capsule). The most sensitive screening test is the **Cryptococcal Antigen (CrAg)** in CSF or serum. * **Culture:** Grows on **Sabouraud Dextrose Agar (SDA)**; produces urease and forms brown/black colonies on **Niger Seed Agar**. * **Pathology:** "Soap bubble" lesions may be seen in the basal ganglia on MRI. * **Treatment:** Induction with **Amphotericin B + Flucytosine**, followed by maintenance with **Fluconazole**.

Q: What is the causative organism of boggy swelling of hair?

Trichophyton mentagrophytes. **Explanation:** The clinical presentation of a "boggy swelling" of the scalp is known as a **Kerion**. This is an inflammatory, painful, and crusting lesion of the scalp (Tinea capitis) that often leads to scarring alopecia. 1. **Why Trichophyton mentagrophytes is correct:** Kerion is typically caused by **zoophilic** (animal-to-human) or **geophilic** (soil-to-human) dermatophytes. *Trichophyton mentagrophytes* (specifically the *mentagrophytes* variety) is a common zoophilic organism that triggers a vigorous cell-mediated immune response in the host, leading to the characteristic inflammatory boggy swelling. 2. **Why the other options are incorrect:** * **E. floccosum:** This is an anthropophilic fungus that primarily affects the skin (Tinea cruris/pedis) and nails. Crucially, *Epidermophyton* species **never** infect hair. * **M. canis:** While *Microsporum canis* is zoophilic and can cause Tinea capitis, it typically presents as "Gray Patch" (non-inflammatory) or mildly inflammatory lesions. It is less commonly associated with the severe, suppurative Kerion compared to *T. mentagrophytes* or *T. verrucosum*. * **T. concentricum:** This organism is the causative agent of **Tinea imbricata**, characterized by distinctive concentric rings of scales. It does not typically cause boggy scalp swellings. **NEET-PG Clinical Pearls:** * **Kerion:** Inflammatory Tinea capitis; most common causes are *T. verrucosum* (cattle) and *T. mentagrophytes* (rodents). * **Favus:** Characterized by **scutula** (cup-shaped crusts) and mousy odor, caused by *T. schoenleinii*. * **Wood’s Lamp:** *Microsporum* species show bright green fluorescence; *Trichophyton* species (except *T. schoenleinii*) generally do not fluoresce. * **Treatment:** Oral Griseofulvin is the traditional gold standard for Tinea capitis.

Q: Which of the following is a true yeast?

Cryptococcus. **Explanation:** In medical mycology, fungi are classified morphologically into four groups: yeasts, yeast-like fungi, molds, and dimorphic fungi. **1. Why Cryptococcus is the correct answer:** **Cryptococcus neoformans** is a **true yeast**. By definition, true yeasts are unicellular fungi that reproduce solely by budding and do not produce true hyphae or pseudohyphae under any conditions. A key diagnostic feature of *Cryptococcus* is its prominent polysaccharide capsule (visualized by India Ink), which is a major virulence factor. **2. Analysis of Incorrect Options:** * **Candida (Option A):** This is a **yeast-like fungus**. While it grows as budding yeast cells, it also forms **pseudohyphae** (elongated cells that remain attached) when invading tissues. *Candida albicans* can also form true hyphae (germ tubes). * **Aspergillus (Option D) & Rhizopus (Option C):** These are **molds (filamentous fungi)**. They grow as multicellular filaments called hyphae. *Aspergillus* is characterized by septate hyphae with acute-angle branching, while *Rhizopus* features broad, non-septate hyphae with right-angle branching. **Clinical Pearls for NEET-PG:** * **Cryptococcus:** Most common cause of fungal meningitis in HIV/AIDS patients (CD4 <100). Diagnosis is via India Ink (negative staining), Latex Agglutination (detects capsular antigen), and Bird Seed Agar (Niger Seed Agar). * **Candida:** The "Germ Tube Test" (Reynolds-Braude phenomenon) is the gold standard for identifying *C. albicans*. * **Morphology Rule:** If it forms pseudohyphae, it is "yeast-like"; if it only buds, it is a "true yeast."

Q: Candida albicans can be differentiated from other Candida species on cornmeal agar by its unique ability to form which of the following?

Chlamydospores. ### Explanation **Correct Option: C. Chlamydospores** *Candida albicans* is uniquely identified on **Cornmeal Agar (CMA)** by the production of **thick-walled, terminal resting spores called Chlamydospores**. CMA is a nutritionally deficient medium that induces stress in the fungus, stimulating the formation of these characteristic structures. This is a definitive morphological test used in laboratories to differentiate *C. albicans* (and the closely related *C. dubliniensis*) from other non-albicans species. **Analysis of Incorrect Options:** * **A. Aseptate hyphae:** These are characteristic of Zygomycetes (e.g., *Rhizopus*, *Mucor*). *Candida* species are yeasts that produce septate pseudohyphae and true hyphae. * **B. Germ tubes:** While the **Germ Tube Test (Reynolds-Braude phenomenon)** is a rapid diagnostic test for *C. albicans*, it is performed using **human or rabbit serum** incubated at 37°C for 2–3 hours, not on cornmeal agar. * **D. Arthrospores:** These are formed by the fragmentation of hyphae and are characteristic of fungi like *Trichosporon* and *Geotrichum candidum*, but not *Candida*. **High-Yield Clinical Pearls for NEET-PG:** * **Germ Tube Test:** The earliest morphological change in *C. albicans* when shifted from 25°C to 37°C in serum. * **Phenotypic Switching:** *C. albicans* can switch between yeast (commensal) and hyphal (pathogenic/invasive) forms. * **C. dubliniensis:** The only other species that produces chlamydospores and is germ tube positive; it is typically differentiated by its inability to grow at 45°C. * **CHROMagar:** A specialized differential medium where *C. albicans* produces characteristic **light green** colonies.

Q: An examination of sputum for a suspected case of fungal infection may reveal hyphae in which of the following conditions?

Aspergillosis. **Explanation:** The correct answer is **Aspergillosis**. **Why Aspergillosis is correct:** *Aspergillus* species are filamentous fungi characterized by the presence of **septate hyphae** that typically show **dichotomous branching at acute angles (45°)**. In clinical practice, when *Aspergillus* involves the lungs (such as in an Aspergilloma or Invasive Pulmonary Aspergillosis), these characteristic hyphae can be directly visualized in the sputum or bronchoalveolar lavage (BAL) fluid using KOH mounts or silver stains. **Analysis of Incorrect Options:** * **Sporotrichosis:** Caused by *Sporothrix schenckii*, a dimorphic fungus. In tissue or clinical samples (yeast phase), it typically appears as **cigar-shaped budding yeasts**, not hyphae. * **Histoplasmosis:** *Histoplasma capsulatum* is an intracellular dimorphic fungus. In sputum or tissue, it is seen as **small, oval budding yeasts** within macrophages. Hyphae are only seen in the mold form at room temperature in the lab. * **Cryptococcosis:** *Cryptococcus neoformans* is a monomorphic yeast. It is characterized by **spherical, encapsulated budding yeasts**. It never forms true hyphae; its hallmark is the thick polysaccharide capsule visualized by India Ink. **NEET-PG High-Yield Pearls:** * **Aspergillus:** Look for "Acute angle branching" and "Septate hyphae." * **Mucor/Rhizopus:** Look for "Right angle (90°) branching" and "Aseptate/Coenocytic hyphae." * **Dimorphic Fungi Rule:** They exist as **M**old in the **C**old (25°C - hyphae) and **Y**east in the **B**east (37°C/Body - yeast). Since sputum is a clinical sample from the body, you expect the yeast form for *Sporothrix* and *Histoplasma*.

Q: Fever with pulmonary disease leading to severe pneumonia if untreated, caused by which of the following dimorphic fungi?

Coccidioides immitis. ### Explanation **Correct Option: A. Coccidioides immitis** *Coccidioides immitis* is a classic **dimorphic fungus** (existing as mold in soil and spherules in tissue). It is the causative agent of **Valley Fever**. While many infections are asymptomatic, it can present as a self-limiting respiratory illness or progress to **severe pneumonia** and disseminated disease in immunocompromised individuals. It is highly infectious; inhalation of a few arthroconidia can lead to disease. **Analysis of Incorrect Options:** * **B. Cryptococcus neoformans:** This is an **encapsulated yeast**, not a dimorphic fungus. While it can cause pulmonary nodules, it is most notorious for causing subacute or chronic meningitis in HIV/AIDS patients. * **C. Candida albicans:** This is a **yeast** (forming pseudohyphae and germ tubes), not dimorphic in the traditional sense (mold-to-yeast). It typically causes opportunistic infections like oral thrush or candidemia rather than primary severe pneumonia in immunocompetent hosts. * **D. Aspergillus:** This is a **monomorphic filamentous fungus** (mold only) characterized by septate hyphae with acute-angle branching. It causes Aspergilloma or Invasive Aspergillosis, but it does not exhibit dimorphism. **High-Yield Clinical Pearls for NEET-PG:** * **Dimorphic Fungi Mnemonic:** "**B**ody **H**as **C**apsule **S**haped **P**arasites" (**B**lastomyces, **H**istoplasma, **C**occidioides, **S**porothrix, **P**aracoccidioides). * **Morphology:** In the body (37°C), *Coccidioides* forms **Spherules filled with endospores** (unique because it doesn't form yeast cells). * **Geography:** Associated with the Southwestern US (California, Arizona) and alkaline desert soil. * **Diagnosis:** Identification of spherules in sputum or biopsy; culture is hazardous and must be handled in Biosafety Level 3 (BSL-3).

Q: In an asthmatic patient, the causative agent was found to be fungi with septate hyphae. What is the organism?

Aspergillus. ### Explanation The correct answer is **Aspergillus**. This question tests the clinical and morphological identification of medically important fungi. **1. Why Aspergillus is correct:** * **Morphology:** *Aspergillus* species are characterized by **narrow, septate hyphae** that exhibit **dichotomous branching** (branching at acute angles, approximately 45°). * **Clinical Correlation:** There is a strong association between *Aspergillus* and asthma, specifically in a condition known as **Allergic Bronchopulmonary Aspergillosis (ABPA)**. In ABPA, the fungus colonizes the bronchial tree, triggering a Type I (IgE-mediated) and Type III hypersensitivity reaction in asthmatic or cystic fibrosis patients. **2. Why the other options are incorrect:** * **Candida:** While it can cause pulmonary infections in severely immunocompromised hosts, it typically presents as **budding yeast cells and pseudohyphae** (except *C. albicans*, which forms true hyphae/germ tubes). It is not classically associated with asthma. * **Mucor:** These belong to the Zygomycetes family and are characterized by **broad, aseptate (coenocytic) hyphae** with right-angle (90°) branching. They typically cause Rhino-orbito-cerebral mucormycosis in diabetic patients. * **Cryptococcus:** This is an **encapsulated yeast** (not hyphal). It is identified using India Ink and is most commonly associated with meningitis in HIV patients. **3. NEET-PG High-Yield Pearls:** * **ABPA Diagnostic Criteria:** Look for asthma, fleeting pulmonary opacities, peripheral eosinophilia, and very high serum IgE levels (>1000 IU/mL). * **Culture:** *Aspergillus* grows on Sabouraud Dextrose Agar (SDA), producing "smoky green" colonies (*A. fumigatus*). * **Microscopy:** The fruiting body consists of a conidiophore ending in a swollen vesicle covered with sterigmata (phialides).

Q: A diabetic patient presents with pus from the eye. Colonies of the isolated organism are black with microscopic features of non-septate hyphae and obtuse branching. What is the diagnosis?

Mucormycosis. ### Explanation **1. Why Mucormycosis is the Correct Answer:** The diagnosis is based on a combination of clinical presentation and classic morphological features: * **Clinical Context:** Diabetes mellitus (especially with ketoacidosis) is the most significant risk factor for **Rhino-oculo-cerebral Mucormycosis**. * **Microscopic Morphology:** The hallmark of Mucorales (e.g., *Rhizopus*, *Mucor*) is **broad, non-septate (coenocytic) hyphae** with **obtuse-angle (90°) branching**. * **Gross Appearance:** These fungi grow rapidly as "lid-lifters" with a cottony texture that turns **black/greyish** due to the production of pigmented sporangia. **2. Why Other Options are Incorrect:** * **Aspergillosis:** Characterized by **septate hyphae** with **acute-angle (45°) branching**. While it can cause ocular infections, the branching pattern described is pathognomonic for Mucormycosis. * **Candidiasis:** Typically presents as **budding yeast cells** and **pseudohyphae**. It does not form non-septate hyphae or black colonies with obtuse branching. * **Histoplasmosis:** A dimorphic fungus that exists as small, intracellular yeasts within macrophages at body temperature. It does not present with the described hyphal morphology. **3. NEET-PG High-Yield Pearls:** * **Angioinvasion:** Mucorales have a predilection for invading blood vessels, leading to thrombosis and tissue necrosis (black eschar). * **Specimen Handling:** Never grind or homogenize the tissue biopsy for Mucor; it destroys the fragile non-septate hyphae. Always use **tease mount** or **mincing**. * **Drug of Choice:** Liposomal **Amphotericin B** is the gold standard treatment, along with aggressive surgical debridement. * **Stains:** Best visualized using KOH mount, Calcofluor white, or silver stains (GMS).

Q: Which of the following statements about Pneumocystis jiroveci is false?

Ampicillin is the drug of choice for treatment.. **Explanation:** *Pneumocystis jirovecii* (formerly *P. carinii*) is a unique unicellular fungus that lacks ergosterol in its cell membrane, making it resistant to standard antifungal agents like Amphotericin B. **Why Option B is the Correct Answer (False Statement):** The drug of choice for *Pneumocystis* pneumonia (PCP) is **Trimethoprim-Sulfamethoxazole (TMP-SMX)**, not Ampicillin. Ampicillin is a beta-lactam antibiotic used for bacterial infections and has no activity against fungi. In patients with sulfonamide allergies, alternative treatments include Pentamidine or Clindamycin-Primaquine. **Analysis of Other Options:** * **Option A:** It is an **opportunistic pathogen**. It is the most common opportunistic infection in HIV/AIDS patients (typically when CD4 counts fall below 200 cells/µL) and those on long-term immunosuppressants. * **Option C:** Radiologically, PCP typically presents with bilateral ground-glass opacities. However, it is well-known for causing **pneumatoceles** (thin-walled air-filled cysts), which can rupture leading to spontaneous pneumothorax. * **Option D:** Diagnosis can be made via microscopy of **induced sputum** or Bronchoalveolar Lavage (BAL). Since the organism cannot be cultured, stains like **Gomori Methenamine Silver (GMS)**—which highlights crushed-ping-pong-ball shaped cysts—or Direct Fluorescent Antibody (DFA) testing are used. **High-Yield Clinical Pearls for NEET-PG:** * **Classification:** Previously classified as a protozoan, now classified as a **fungus** based on nucleic acid analysis. * **Stains:** GMS (best for cysts), Giemsa (for trophozoites), and Toluidine blue O. * **Serum Marker:** Elevated **Beta-D-Glucan** levels are often seen (non-specific but suggestive). * **Prophylaxis:** Indicated in HIV patients when CD4 count is **<200 cells/µL**.

Q: What is the most common cause of bronchopulmonary aspergillosis?

Aspergillus fumigatus. ### Explanation **Correct Answer: A. Aspergillus fumigatus** **1. Why it is correct:** *Aspergillus fumigatus* is the most common species implicated in all forms of aspergillosis, including **Allergic Bronchopulmonary Aspergillosis (ABPA)**. It is a ubiquitous saprophytic fungus with small, thermotolerant spores (conidia) that are easily inhaled into the lower respiratory tract. In susceptible individuals (typically those with asthma or cystic fibrosis), these spores germinate into hyphae, triggering a complex Type I (IgE-mediated) and Type III (IgG-mediated) hypersensitivity reaction, leading to airway inflammation and bronchiectasis. **2. Why the other options are incorrect:** * **Aspergillus clavatus:** While it can cause hypersensitivity pneumonitis (specifically "Malt worker’s lung"), it is a rare cause of ABPA. * **Aspergillus flavus:** This is the second most common clinical isolate. It is more frequently associated with invasive aspergillosis in immunocompromised patients and **paranasal sinus infections**, but it is less common than *A. fumigatus* in ABPA. * **Aspergillus niger:** Characterized by black conidia, it is a common cause of **otomycosis** (fungal ear infection) and aspergilloma, but rarely triggers the specific allergic response seen in ABPA. **3. High-Yield Clinical Pearls for NEET-PG:** * **ABPA Diagnosis:** Look for the triad of **Asthma**, **Eosinophilia**, and **Fleeting pulmonary opacities** on X-ray. * **Radiology:** "Finger-in-glove" appearance due to mucoid impaction and central bronchiectasis. * **Laboratory:** Elevated total serum IgE (>1000 IU/mL) and specific IgE/IgG against *A. fumigatus*. * **Morphology:** *Aspergillus* species show **septate hyphae** with **dichotomous branching at acute angles (45°)**. * **Treatment:** Oral corticosteroids (to reduce inflammation) and Itraconazole (to reduce fungal load).

Question 1

What is the most common organism causing meningitis in a patient with AIDS?

Accepted Answer

Cryptococcus neoformans

Answer

Candida albicans

Answer

Streptococcus pneumoniae

Answer

Haemophilus influenzae

Question 2

What is the causative organism of boggy swelling of hair?

Accepted Answer

Trichophyton mentagrophytes

Answer

E. flocosum

Answer

M. canis

Answer

T. concentricum

Question 3

Which of the following is a true yeast?

Accepted Answer

Cryptococcus

Answer

Candida

Answer

Rhizopus

Answer

Aspergillus

Question 4

Candida albicans can be differentiated from other Candida species on cornmeal agar by its unique ability to form which of the following?

Accepted Answer

Chlamydospores

Answer

Aseptate hyphae

Answer

Germ tubes

Answer

Arthrospores

Question 5

An examination of sputum for a suspected case of fungal infection may reveal hyphae in which of the following conditions?

Accepted Answer

Aspergillosis

Answer

Sporotrichosis

Answer

Histoplasmosis

Answer

Cryptococcosis

Question 6

Fever with pulmonary disease leading to severe pneumonia if untreated, caused by which of the following dimorphic fungi?

Accepted Answer

Coccidioides immitis

Answer

Cryptococcus neoformans

Answer

Candida albicans

Answer

Aspergillus

Question 7

In an asthmatic patient, the causative agent was found to be fungi with septate hyphae. What is the organism?

Accepted Answer

Aspergillus

Answer

Candida

Answer

Mucor

Answer

Cryptococcus

Question 8

A diabetic patient presents with pus from the eye. Colonies of the isolated organism are black with microscopic features of non-septate hyphae and obtuse branching. What is the diagnosis?

Accepted Answer

Mucormycosis

Answer

Aspergillosis

Answer

Candidiasis

Answer

Histoplasmosis

Question 9

Which of the following statements about Pneumocystis jiroveci is false?

Accepted Answer

Ampicillin is the drug of choice for treatment.

Answer

It is primarily seen in immunocompromised individuals.

Answer

It may be associated with pneumatocele formation.

Answer

It can be diagnosed with sputum microscopy.

Question 10

What is the most common cause of bronchopulmonary aspergillosis?

Accepted Answer

Aspergillus fumigatus

Answer

Aspergillus clavatus

Answer

Aspergillus flavus

Answer

Aspergillus niger

Mycology — MCQs

Mycology — MCQs

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