Mycology Practice Questions

Q: Which of the following fungal infections is a leading cause of corneal ulcer?

Aspergillus. **Explanation:** **1. Why Aspergillus is the correct answer:** Mycotic keratitis (fungal corneal ulcer) is a significant cause of ocular morbidity, especially in tropical regions. **Aspergillus species** (particularly *A. flavus* and *A. fumigatus*) are the most common cause of fungal corneal ulcers worldwide, followed closely by *Fusarium*. These infections typically occur following **vegetative trauma** (e.g., injury with a branch, leaf, or agricultural tool), which introduces the conidia into the corneal stroma. Clinically, these ulcers often present with "feathery" borders, satellite lesions, and a dry, gray-white appearance. **2. Why the other options are incorrect:** * **Trichophyton:** This is a dermatophyte responsible for superficial infections of the skin, hair, and nails (Tinea). It does not typically involve the cornea. * **Mucor:** While *Mucor* species cause devastating Rhinocerebral Mucormycosis (especially in uncontrolled diabetics), they primarily cause orbital cellulitis and tissue necrosis through angioinvasion rather than isolated corneal ulcers. * **Sporothrix:** *Sporothrix schenckii* causes "Rose gardener’s disease" (lymphocutaneous sporotrichosis). While it can rarely cause ocular adnexal infection, it is not a leading cause of keratitis. **3. NEET-PG High-Yield Pearls:** * **Most common cause overall:** *Aspergillus* (filamentous fungi). * **Most common cause in contact lens users:** *Acanthamoeba* or *Pseudomonas*. * **Classic Clinical Sign:** Feathery margins and **satellite lesions** (small infiltrates away from the main ulcer). * **Diagnosis:** Potassium Hydroxide (KOH) mount of corneal scrapings is the rapid test of choice; Sabouraud Dextrose Agar (SDA) is used for culture. * **Drug of Choice:** Topical **Natamycin** (5%) is the gold standard for filamentous fungal keratitis.

Q: Which of the following organisms is NOT typically cultured in a laboratory setting?

Rhinosporidium seeberi. **Explanation:** The correct answer is **Rhinosporidium seeberi**. **1. Why Rhinosporidium seeberi is the correct answer:** *Rhinosporidium seeberi* is a unique organism (historically classified as a fungus but now considered a protist belonging to the Mesomycetozoea group) that causes **Rhinosporidiosis**. The defining characteristic of this organism is that it **cannot be cultured on artificial laboratory media** (like SDA) or in cell lines. Diagnosis relies exclusively on clinical presentation and histopathology, where large, thick-walled **sporangia** containing thousands of **endospores** are visualized. **2. Why the other options are incorrect:** * **Sporothrix schenckii (A):** This is a dimorphic fungus that can be easily cultured. At 25°C, it grows as a mold (flower-like sporulation), and at 37°C, it grows as cigar-shaped yeast cells. * **Candida albicans (C):** This is the most common fungal isolate in clinical labs. It grows rapidly on Sabouraud Dextrose Agar (SDA) as creamy white colonies and produces germ tubes in serum. * **Aspergillus fumigatus (D):** This is a ubiquitous filamentous fungus that grows well on standard media, producing characteristic smoky-green velvety colonies with distinct conidiophores. **3. High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** Rhinosporidiosis typically presents as leafy, friable, strawberry-like **polypoidal masses** in the nose or nasopharynx. * **Epidemiology:** Highly prevalent in South India (especially Tamil Nadu and Kerala) and Sri Lanka; often associated with bathing in stagnant water. * **Histopathology:** Look for the "Sporangium" (up to 350 µm)—much larger than the spherules of *Coccidioides*. * **Treatment:** Surgical excision with electrocautery of the base is the treatment of choice; medical therapy (Dapsone) has limited efficacy.

Q: Blastomycosis may involve any of the following organs except?

Intestinal tract. **Explanation:** **Blastomycosis**, caused by the dimorphic fungus *Blastomyces dermatitidis*, is primarily a systemic pyogranulomatous infection. The correct answer is **Intestinal tract** because Blastomycosis is known for its predilection for the respiratory system and subsequent hematogenous spread to specific extrapulmonary sites, but it **rarely, if ever, involves the gastrointestinal tract.** 1. **Why Intestinal tract is correct:** Unlike *Histoplasmosis* (which frequently involves the reticuloendothelial system and can cause GI ulcerations), Blastomycosis does not typically affect the intestines. It is an "except" question, and the GI tract is not a recognized clinical feature of the disease. 2. **Why other options are incorrect:** * **Lungs (B):** The primary route of infection is inhalation of conidia. Pulmonary involvement is the most common presentation, ranging from asymptomatic infection to acute pneumonia or ARDS. * **Skin (A):** This is the most common **extrapulmonary** site (approx. 40-80% of cases). It presents as verrucous lesions with microabscesses or ulcerative lesions. * **Lymphatics (C):** While less common than skin or bone involvement, lymphadenopathy can occur as part of the systemic spread or secondary to pulmonary infection. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** In tissue (yeast form), it shows characteristic **Broad-Based Budding** with a thick, doubly refractile cell wall ("B" for Blastomyces, "B" for Broad-Based). * **Geography:** Endemic to the Ohio and Mississippi River valleys (similar to Histoplasma). * **Common Sites of Spread:** Remember the mnemonic **"LBS"** — **L**ungs, **B**one (osteomyelitis), and **S**kin. It also frequently involves the **Prostate** in males. * **Diagnosis:** KOH mount of sputum or skin scrapings; Culture on Sabouraud Dextrose Agar (SDA).

Q: A patient develops fever, shortness of breath, and appears to be quite ill. X-ray demonstrates bilateral interstitial lung infiltrates. Bronchial washings demonstrate small "hat-shape" organisms visible on silver stain within alveoli. Which predisposing condition is most likely to be present in this patient?

AIDS. ### Explanation The clinical presentation and microscopic findings point directly to **Pneumocystis pneumonia (PCP)**, caused by the fungus ***Pneumocystis jirovecii***. **1. Why the correct answer is right:** * **Clinical Presentation:** The triad of fever, dyspnea, and **bilateral interstitial (ground-glass) infiltrates** on X-ray is classic for PCP. * **Microscopy:** *P. jirovecii* cannot be cultured. Diagnosis relies on staining (Gomori Methenamine Silver - GMS). The description of **"hat-shaped,"** "cup-shaped," or "crushed ping-pong ball" cysts within the alveoli is pathognomonic for this organism. * **Predisposing Condition:** *P. jirovecii* is an opportunistic pathogen. It is the most common opportunistic infection in patients with **AIDS**, typically occurring when the **CD4+ T-cell count falls below 200 cells/mm³**. **2. Why the incorrect options are wrong:** * **Congestive heart failure (CHF):** While CHF causes bilateral infiltrates (pulmonary edema), it would not show silver-staining organisms in bronchial washings. * **Pulmonary embolus:** Usually presents with sudden pleuritic chest pain and a normal X-ray or focal wedge-shaped infarct (Hampton’s hump), not diffuse interstitial infiltrates or fungal cysts. * **Rheumatoid arthritis:** While RA can cause interstitial lung disease (ILD), it is a chronic process and would not demonstrate the specific "hat-shaped" organisms associated with acute infectious pneumonia. **3. NEET-PG High-Yield Pearls:** * **Stains of Choice:** **GMS stain** (best for cysts/hat-shape); **Giemsa/Wright stain** (shows trophic forms); **Direct Fluorescent Antibody (DFA)** is the most sensitive. * **Biochemical Marker:** Elevated **Serum Beta-D-Glucan** (non-specific but supportive). * **Drug of Choice:** **Trimethoprim-Sulfamethoxazole (TMP-SMX)**. * **Prophylaxis:** Indicated in HIV patients when CD4 count is **<200 cells/mm³**.

Q: Which fungal infection is commonly found in patients with uncontrolled diabetes?

Mucormycosis. ### Explanation **Correct Answer: B. Mucormycosis** **Why it is correct:** Mucormycosis (caused by fungi of the order Mucorales, such as *Rhizopus* and *Mucor*) is an opportunistic infection strongly associated with **uncontrolled diabetes mellitus**, particularly during episodes of **Diabetic Ketoacidosis (DKA)**. * **The Mechanism:** These fungi possess an enzyme called **ketone reductase**, which allows them to thrive in acidic, high-glucose environments. Furthermore, DKA causes the release of iron from binding proteins (sequestration failure); the fungi utilize this free iron for rapid growth. The most common presentation in diabetics is **Rhinocerebral Mucormycosis**, characterized by angioinvasion, tissue necrosis (black eschar), and potential spread to the orbit and brain. **Why the other options are incorrect:** * **A. Histoplasmosis:** This is a systemic dimorphic fungal infection typically associated with bird or bat droppings (caves). While it can affect immunocompromised patients, it is not specifically linked to diabetes like Mucormycosis. * **C. Cryptococcosis:** Caused by *Cryptococcus neoformans*, this is the most common fungal meningitis in **HIV/AIDS patients** (CD4 count <100). Its primary association is cellular immunodeficiency rather than metabolic derangement. * **D. Rhinosporidiosis:** Caused by *Rhinosporidium seeberi*, it typically presents as friable, strawberry-like nasal polyps in individuals who bathe in stagnant water. It is not associated with diabetes. **High-Yield Clinical Pearls for NEET-PG:** * **Hallmark:** Broad, **non-septate** hyphae with **right-angle (90°)** branching. * **Clinical Sign:** A **black eschar** on the palate or nasal turbinates is a classic board-exam clue. * **Treatment:** Surgical debridement and **Liposomal Amphotericin B**. (Note: Voriconazole is ineffective against Mucor). * **Risk Factors:** DKA, neutropenia, and iron overload (use of deferoxamine).

Q: Eucalyptus camaldulensis is associated with the transmission of which of the following fungi?

Cryptococcus. **Explanation:** The correct answer is **Cryptococcus**, specifically **Cryptococcus gattii**. **1. Why Cryptococcus is correct:** While *Cryptococcus neoformans* is famously associated with pigeon droppings, *Cryptococcus gattii* has a strong ecological niche in decaying hollows of certain trees. **Eucalyptus camaldulensis** (River Red Gum) and *Eucalyptus tereticornis* are the primary environmental reservoirs. Inhalation of basidiospores from these trees leads to infection. Unlike *C. neoformans*, which primarily affects immunocompromised patients, *C. gattii* is known to cause disease in **immunocompetent** individuals, often presenting with large pulmonary or CNS fungal granulomas (cryptococcomas). **2. Why the other options are incorrect:** * **Blastomyces dermatitidis:** Found in moist soil and decomposing organic matter (wood/leaves), primarily near waterways in the Mississippi and Ohio River valleys. It is not specifically linked to Eucalyptus. * **Histoplasma capsulatum:** Classically associated with soil enriched with **bird or bat guano** (caves, chicken coops). * **Coccidioides immitis:** Found in the alkaline, **semi-arid desert soil** of the Southwestern United States (San Joaquin Valley). **3. High-Yield Clinical Pearls for NEET-PG:** * **Stains:** Cryptococcus is best visualized using **India Ink** (negative staining showing the polysaccharide capsule) or **Mucicarmine** (stains the capsule red). * **Antigen Detection:** The **CrAg (Cryptococcal Antigen)** test via Latex Agglutination or LFA is the most sensitive diagnostic tool. * **C. gattii vs. C. neoformans:** *C. gattii* can be differentiated on **Canavanine-Glycine-Bromothymol Blue (CGB) agar**, where it turns the medium blue. * **Virulence Factor:** The thick polysaccharide capsule is the primary virulence factor, inhibiting phagocytosis.

Q: A diabetic patient presents with a black necrotic mass filling the nasal cavity. What is the most likely fungal infection?

Mucormycosis. ### Explanation **Correct Answer: C. Mucormycosis** **Why it is correct:** The clinical presentation of a **diabetic patient** (especially one in ketoacidosis) with a **black necrotic mass** (eschar) in the nasal cavity is a classic hallmark of **Rhinocerebral Mucormycosis**. The underlying medical concept is **angioinvasion**: the fungi (genera *Rhizopus*, *Mucor*, and *Lichtheimia*) invade blood vessel walls, leading to thrombosis and subsequent tissue infarction/necrosis. This necrosis manifests as the characteristic black eschar. High glucose levels and acidic pH (in DKA) provide an ideal environment for these fungi to thrive by increasing free iron availability. **Why the other options are incorrect:** * **Rhinosporidiosis (A):** Caused by *Rhinosporidium seeberi*, it typically presents as a friable, leafy, strawberry-like polypoid mass in the nose, usually following exposure to stagnant water. It does not cause black necrosis. * **Aspergillosis (B):** While *Aspergillus* can cause invasive sinusitis in immunocompromised patients, it is less specifically associated with diabetic ketoacidosis and is not the "classic" cause of the rapid, black necrotic eschar described in board exams. * **Candidiasis (D):** *Candida* typically causes mucosal surfaces to show white patches (thrush) or pseudomembranes. It does not typically present as an invasive, necrotic nasal mass. **High-Yield Clinical Pearls for NEET-PG:** * **Microscopy:** Look for **broad, aseptate hyphae** branching at **right angles (90°)**. * **Risk Factors:** Uncontrolled Diabetes (DKA), Neutropenia, and Iron overload (Deferoxamine use). * **Treatment:** Surgical debridement + **Liposomal Amphotericin B** (Drug of choice). * **Culture:** Grows on Sabouraud Dextrose Agar (SDA) as "cotton candy" colonies.

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: 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.

Question 1

Which of the following fungal infections is a leading cause of corneal ulcer?

Accepted Answer

Aspergillus

Answer

Trichophyton

Answer

Mucor

Answer

Sporothrix

Question 2

Which of the following organisms is NOT typically cultured in a laboratory setting?

Accepted Answer

Rhinosporidium seeberi

Answer

Sporothrix schenckii

Answer

Candida albicans

Answer

Aspergillus fumigatus

Question 3

Blastomycosis may involve any of the following organs except?

Accepted Answer

Intestinal tract

Answer

Skin

Answer

Lungs

Answer

Lymphatics

Question 4

A patient develops fever, shortness of breath, and appears to be quite ill. X-ray demonstrates bilateral interstitial lung infiltrates. Bronchial washings demonstrate small "hat-shape" organisms visible on silver stain within alveoli. Which predisposing condition is most likely to be present in this patient?

Accepted Answer

AIDS

Answer

Congestive heart failure

Answer

Pulmonary embolus

Answer

Rheumatoid arthritis

Question 5

Which fungal infection is commonly found in patients with uncontrolled diabetes?

Accepted Answer

Mucormycosis

Answer

Histoplasmosis

Answer

Cryptococcosis

Answer

Rhinosporidiosis

Question 6

Eucalyptus camaldulensis is associated with the transmission of which of the following fungi?

Accepted Answer

Cryptococcus

Answer

Blastomyces dematitidis

Answer

Histoplasma

Answer

Coccidioides immitis

Question 7

A diabetic patient presents with a black necrotic mass filling the nasal cavity. What is the most likely fungal infection?

Accepted Answer

Mucormycosis

Answer

Rhinosporidiosis

Answer

Aspergillosis

Answer

Candidiasis

Question 8

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 9

What is the causative organism of boggy swelling of hair?

Accepted Answer

Trichophyton mentagrophytes

Answer

E. flocosum

Answer

M. canis

Answer

T. concentricum

Question 10

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

Mycology — MCQs

Mycology — MCQs

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