Mycology Practice Questions

Q: A 31-year-old HIV-positive man develops a severe pneumonia. Lower respiratory tract secretions obtained by fiberoptic bronchoscopy with bronchoalveolar lavage and stained with methenamine silver stain demonstrate cup-shaped cysts with sharply outlined walls. Which of the following organisms is the most likely pathogen in this case?

Pneumocystis jirovecii. **Explanation:** The clinical presentation and laboratory findings are classic for **Pneumocystis Pneumonia (PCP)**, caused by *Pneumocystis jirovecii*. **1. Why the Correct Answer is Right:** *Pneumocystis jirovecii* is an opportunistic fungus and the most common opportunistic infection in HIV patients with a **CD4 count <200 cells/mm³**. The pathognomonic finding on **Gomori Methenamine Silver (GMS) stain** is the presence of **cup-shaped or crushed ping-pong ball-shaped cysts** (5–8 µm) with dark, eccentric thickening (intracystic bodies). Bronchoalveolar lavage (BAL) is the gold-standard diagnostic procedure due to its high sensitivity. **2. Why Incorrect Options are Wrong:** * **A. Candida albicans:** While common in HIV, it typically causes oral thrush or esophagitis. On silver stain, it shows budding yeasts and **pseudohyphae**, not cup-shaped cysts. * **B. Giardia lamblia:** This is an intestinal protozoan causing malabsorptive diarrhea. It is not a respiratory pathogen and would be identified in stool samples as pear-shaped trophozoites. * **C. Haemophilus influenzae:** This is a gram-negative coccobacillus. It causes bacterial pneumonia (lobar consolidation) and would be visualized on a Gram stain, not a silver stain. **3. High-Yield Clinical Pearls for NEET-PG:** * **Chest X-ray:** Characteristically shows bilateral, symmetrical **perihilar "ground-glass" opacities**. * **Laboratory:** Elevated **Serum LDH** levels are a sensitive but non-specific marker for PCP. * **Stains:** Besides GMS, **Toluidine blue O** also stains cysts; **Giemsa/Wright stain** is used for trophic forms. * **Treatment:** The drug of choice is **Trimethoprim-Sulfamethoxazole (TMP-SMX)**. Steroids are added if PaO₂ 35 mmHg.

Q: A 25-year-old female complains of recurrent rhinitis, nasal discharge, and bilateral nasal blockage for one year. She has a history of asthma and allergies. On examination, multiple ethmoidal polyps are noted with mucosal thickening and impacted secretions in both nasal cavities. A biopsy is taken and cultured, showing growth of many hyphae and pseudohyphae with dichotomous branching typically at 45°. Which of the following is the most likely responsible organism?

Aspergillus fumigatus. **Explanation:** The clinical presentation describes a classic case of **Allergic Fungal Rhinosinusitis (AFRS)**. The patient exhibits the characteristic triad: recurrent nasal polyposis, a history of Type I hypersensitivity (asthma/allergies), and "impacted secretions" (allergic mucin). **Why Option A is Correct:** The definitive diagnostic clue lies in the morphology of the fungus. **Aspergillus fumigatus** is characterized by septate hyphae that exhibit **dichotomous branching at acute angles (typically 45°)**. In AFRS, the fungus acts as an allergen rather than an invasive pathogen, leading to the formation of thick, peanut-butter-like eosinophilic mucin and ethmoidal polyps. **Why Other Options are Incorrect:** * **B & C (Rhizopus and Mucor):** These belong to the order Mucorales. They are characterized by **broad, ribbon-like, non-septate hyphae** with **right-angle (90°) branching**. Clinically, they cause invasive, life-threatening Rhino-oculo-cerebral Mucormycosis, typically in immunocompromised or diabetic patients, rather than chronic allergic polyposis. * **D (Candida):** While Candida shows pseudohyphae and budding yeast cells, it is not a common primary cause of fungal rhinosinusitis or nasal polyposis. It lacks the specific 45° dichotomous branching pattern. **NEET-PG High-Yield Pearls:** * **Bent and Kuhn Criteria:** Used for diagnosing AFRS (includes Type I hypersensitivity, nasal polyposis, characteristic CT findings like hyperattenuation, and positive fungal stain). * **CT Finding:** "Double density" sign or "Ground glass" appearance due to heavy metal (iron/magnesium) deposits in fungal mucin. * **Treatment:** Functional Endoscopic Sinus Surgery (FESS) to clear mucin, followed by long-term **topical/systemic steroids** to prevent recurrence. Antifungals are generally not required as it is an allergic, not infectious, process.

Q: A 6-year-old girl presents with scaly patches on the scalp. Initial diagnostic smears and cultures were negative. Following a few weeks, she developed inflammatory lesions. Examination revealed hair that fluoresced under Wood's light, and subsequent smears showed septate hyphae. The family owns several pets. Which of the following is the most likely causative agent?

Microsporum canis. ### Explanation The clinical presentation of scaly patches progressing to inflammatory lesions (Kerion) in a child, combined with a history of pet contact and positive Wood’s light fluorescence, is classic for **Tinea Capitis** caused by **Microsporum canis**. **Why Microsporum canis is correct:** * **Zoophilic Nature:** *M. canis* is a zoophilic fungus commonly transmitted from pets (cats/dogs) to humans. * **Fluorescence:** It produces a characteristic **bright blue-green fluorescence** under Wood’s light due to the metabolite pteridine. * **Inflammatory Response:** While it starts as non-inflammatory, it frequently progresses to inflammatory lesions like a Kerion (a boggy, painful inflammatory mass). * **Ectothrix Infection:** It causes an ectothrix pattern (spores outside the hair shaft), which is associated with fluorescence. **Why other options are incorrect:** * **Microsporum audouinii:** An anthropophilic fungus (human-to-human). While it fluoresces, it is less likely given the specific mention of pets and the high inflammatory response. * **Trichophyton rubrum:** The most common cause of Tinea Corporis and Pedis, but it **rarely** causes Tinea Capitis. Furthermore, *Trichophyton* species (except *T. schoenleinii*) do **not** fluoresce under Wood’s light. * **Epidermophyton floccosum:** This fungus affects the skin and nails (Tinea Cruris/Pedis) but **never** infects the hair. **High-Yield Clinical Pearls for NEET-PG:** * **Wood’s Light Fluorescence:** Remember the mnemonic **"M.A.C."** for green fluorescence in Tinea Capitis: *M. audouinii*, *M. canis*, and *M. distortum*. * **Drug of Choice:** Oral **Griseofulvin** remains the gold standard for Tinea Capitis, especially for *Microsporum* species. * **Endothrix vs. Ectothrix:** *Trichophyton tonsurans* (most common cause of Tinea Capitis worldwide) causes **Endothrix** infection, does not fluoresce, and presents as "Black Dot" Tinea Capitis.

Q: What is the most common fungal infection in febrile neutropenia?

Candida. **Explanation:** In patients with febrile neutropenia, fungal infections typically emerge as secondary infections after 4–7 days of persistent fever despite broad-spectrum antibiotic therapy [1]. **Why Candida is the correct answer:** **Candida species** are the most common cause of fungal infections in neutropenic patients. The primary reason is the disruption of mucosal barriers (mucositis) caused by chemotherapy, which allows commensal *Candida* from the gastrointestinal or genitourinary tract to enter the bloodstream [1]. Among the species, *Candida albicans* remains the most frequent isolate, though non-albicans species (like *C. tropicalis*) are increasing in prevalence [1]. **Analysis of Incorrect Options:** * **Aspergillus fumigatus (Option D):** This is the most common **mould** (filamentous fungus) and the second most common fungal infection overall. It typically presents as Invasive Pulmonary Aspergillosis (IPA) and is more common in patients with prolonged, profound neutropenia (>10–15 days) [2]. * **Aspergillus niger (Option A):** While a member of the Aspergillus family, it is a less common cause of invasive disease compared to *A. fumigatus* and is more frequently associated with otomycosis. * **Mucormycosis (Option C):** This is an aggressive, angioinvasive infection seen in neutropenic patients and diabetics, but it is significantly rarer than both *Candida* and *Aspergillus*. **High-Yield Clinical Pearls for NEET-PG:** * **First-line Fungal Prophylaxis:** Fluconazole or Posaconazole (depending on the risk profile). * **Empiric Treatment:** If fever persists >4 days, start Echinocandins (e.g., Caspofungin) or Liposomal Amphotericin B [1]. * **Diagnostic Marker:** Beta-D-Glucan assay is used for *Candida* and *Aspergillus*, while Galactomannan is specific for *Aspergillus* [2]. * **Imaging:** The "Halo Sign" on CT chest is highly suggestive of early Invasive Aspergillosis [2].

Q: Which of the following dermatophytes is spread from animals to humans?

Trichophyton verrucosum. ### Explanation Dermatophytes are classified into three groups based on their primary host and habitat: **Anthropophilic** (humans), **Zoophilic** (animals), and **Geophilic** (soil). Understanding this classification is high-yield for NEET-PG, as it dictates the clinical presentation and source of infection. **Why Option D is Correct:** **Trichophyton verrucosum** is a **zoophilic** dermatophyte. Its primary hosts are cattle. Humans typically acquire the infection through direct contact with infected livestock or contaminated farm equipment. Zoophilic infections in humans often trigger a more intense inflammatory response compared to anthropophilic species, frequently presenting as a **Kerion** (a painful, inflammatory boggy mass on the scalp). **Analysis of Incorrect Options:** * **A. Trichophyton rubrum:** This is the most common **anthropophilic** dermatophyte worldwide. it is the leading cause of Tinea pedis, Tinea cruris, and Onychomycosis. It typically causes chronic, non-inflammatory infections. * **B. Trichophyton tonsurans:** An **anthropophilic** fungus and the leading cause of epidemic Tinea capitis (Endothrix infection) in children. It is spread via human-to-human contact or fomites (combs, hats). * **C. Epidermophyton floccosum:** (Note: Option C lists *Trichophyton floccosum*, but the genus is *Epidermophyton*). It is an **anthropophilic** fungus that affects the skin and nails but **never the hair**. **NEET-PG Clinical Pearls:** * **Zoophilic species:** *T. verrucosum* (cattle), *T. mentagrophytes* (rodents), *Microsporum canis* (cats/dogs). * **Geophilic species:** *Microsporum gypseum* (soil). * **Inflammation Level:** Geophilic/Zoophilic > Anthropophilic. * **Wood’s Lamp:** *M. canis* (Zoophilic) fluoresces bright green, while most *Trichophyton* species (except *T. schoenleinii*) do not.

Q: Which of the following is NOT true about Cryptococcus neoformans?

It produces a germ tube.. **Explanation:** **Why Option C is the correct answer:** The **Germ Tube Test** is a specific diagnostic test used to identify ***Candida albicans*** and *Candida dubliniensis*. When these species are incubated in human or rabbit serum at 37°C for 2–3 hours, they produce true hyphae-like extensions without constriction at the origin (germ tubes). **Cryptococcus neoformans** is an obligate yeast; it does not produce germ tubes, pseudohyphae, or true hyphae in clinical specimens or standard cultures. **Analysis of Incorrect Options:** * **Option A (It is a yeast):** This is true. Unlike many other systemic fungi that are dimorphic, *Cryptococcus* is a monomorphic yeast both at room temperature and at 37°C. * **Option B (It is capsulated):** This is true. Its prominent **polysaccharide capsule** (Glucuronoxylomannan) is its primary virulence factor. It is the only medically important fungus that is routinely identified by its capsule using **India Ink** (negative staining). * **Option D (It can cause meningitis):** This is true. *C. neoformans* is the most common cause of fungal meningitis, particularly in immunocompromised patients (e.g., HIV/AIDS with CD4 counts <100 cells/µL). **High-Yield NEET-PG Pearls:** 1. **Source:** Associated with **pigeon droppings** and soil. 2. **Urease Test:** *Cryptococcus* is **Urease positive** (unlike *Candida*). 3. **Culture:** Grows on Sabouraud Dextrose Agar (SDA); produces **creamy mucoid colonies**. 4. **Phenol Oxidase:** Produces melanin on **Bird Seed Agar** (Niger Seed Agar), appearing as brown/black colonies. 5. **Antigen Detection:** Latex Agglutination test for capsular antigen is more sensitive than India Ink for CSF diagnosis.

Q: What is the drug of choice for paracoccidioidomycosis?

Amphotericin B. **Explanation:** **Paracoccidioidomycosis** (South American Blastomycosis) is a systemic fungal infection caused by the dimorphic fungus *Paracoccidioides brasiliensis*. **Why Amphotericin B is the Correct Answer:** For **severe or disseminated forms** of paracoccidioidomycosis, **Amphotericin B** is the drug of choice for initial induction therapy. It is the most potent antifungal agent and is required to rapidly reduce the fungal burden in life-threatening cases. Following stabilization with Amphotericin B, patients are typically transitioned to long-term maintenance therapy with azoles or sulfonamides. **Analysis of Incorrect Options:** * **Nystatin (A):** This is a polyene antifungal used only for **topical or oral (luminal)** candidiasis. It is not absorbed systemically and is ineffective for deep-seated systemic mycoses. * **Fluconazole (B):** While an azole, it has relatively poor activity against *P. brasiliensis* compared to Itraconazole. It is not the primary choice for systemic management. * **Ketoconazole (C):** Although historically used, it has been largely replaced by **Itraconazole** (the drug of choice for mild-to-moderate cases) due to Ketoconazole’s significant side effects, including hepatotoxicity and inhibition of steroidogenesis. **NEET-PG High-Yield Pearls:** 1. **Microscopic Appearance:** Classically described as a **"Pilot’s wheel"** or **"Mariner’s wheel"** appearance due to multiple budding yeast cells. 2. **Epidemiology:** Primarily found in **South and Central America** (Brazil); often affects agricultural workers. 3. **Clinical Presentation:** Often involves painful **mucocutaneous ulcers** (mouth and nose) and lymphadenopathy. 4. **Maintenance Therapy:** For non-severe cases, **Itraconazole** is the preferred oral agent. Sulfonamides (TMP-SMX) are also an effective, low-cost alternative for long-term suppression.

Q: A patient who recently underwent denture fixation presents with oral thrush that bleeds on scraping. What is the causative agent for this condition?

Candida. **Explanation:** The clinical presentation of white, curd-like patches on the oral mucosa that **bleed upon scraping** (erythematous base) is the hallmark of **Pseudomembranous Candidiasis** (Oral Thrush). In this case, the recent denture fixation is a significant predisposing factor, as dentures can create a microenvironment (stomatitis) conducive to the overgrowth of *Candida albicans*, an opportunistic fungus. **Why the other options are incorrect:** * **Diphtheria:** Caused by *Corynebacterium diphtheriae*, it presents with a "greyish-white pseudomembrane" on the tonsils/pharynx. Unlike Candida, this membrane is tough, leathery, and very difficult to scrape off; attempting to do so causes profuse bleeding. * **Strep Mutans:** This is the primary causative agent of **dental caries** (tooth decay) due to its ability to produce acid from dietary sugars. It does not cause thrush or scrapable white patches. * **Staph Aureus:** While it can cause skin infections or angular cheilitis, it is not the typical cause of white, scrapable oral plaques. **High-Yield Clinical Pearls for NEET-PG:** * **Risk Factors:** Immunosuppression (HIV/AIDS - often the first sign), prolonged antibiotic use, inhaled corticosteroids (asthma), and diabetes mellitus. * **Diagnosis:** KOH mount of the scrapings shows **budding yeast cells and pseudohyphae**. * **Culture:** Grows on **Sabouraud Dextrose Agar (SDA)** as creamy white colonies. *C. albicans* is specifically identified by a positive **Germ Tube Test**. * **Treatment:** Topical Nystatin or oral Fluconazole.

Q: A 50-year-old diabetic female presents with intense pruritus and discharge from the vagina. A smear of the discharge shows budding yeast cells. What is the most likely causative agent?

Candida albicans. ### Explanation The correct answer is **Candida albicans**. **1. Why Candida albicans is correct:** The clinical presentation of intense pruritus, vaginal discharge, and the presence of **budding yeast cells** (and/or pseudohyphae) on a smear is pathognomonic for **Vulvovaginal Candidiasis (VVC)**. * **Risk Factors:** Diabetes mellitus is a major predisposing factor because hyperglycemia increases glycogen levels in vaginal secretions, promoting fungal growth. * **Microscopy:** Budding yeast cells and pseudohyphae are typically seen on a KOH mount or Gram stain. **2. Why the other options are incorrect:** * **Trichomonas vaginalis:** Presents with a profuse, frothy, greenish-yellow discharge and a "strawberry cervix." Microscopy would show motile, flagellated pear-shaped organisms, not yeast. * **Mobiluncus:** This is an anaerobic organism associated with **Bacterial Vaginosis (BV)**. BV is characterized by a "fishy" odor and "clue cells" on microscopy, not budding yeast. * **Chlamydia trachomatis:** Typically causes cervicitis or Pelvic Inflammatory Disease (PID). It is an obligate intracellular bacterium and would not appear as budding yeast on a smear. **3. NEET-PG High-Yield Pearls:** * **Gold Standard Diagnosis:** Culture on **Sabouraud’s Dextrose Agar (SDA)**. * **Clinical Sign:** "Curdy white" or "cottage cheese" like discharge. * **pH Factor:** Unlike Trichomonas and BV (where pH > 4.5), the vaginal pH in Candidiasis is usually **normal (< 4.5)**. * **Treatment:** Fluconazole (oral) or Clotrimazole (topical). In pregnancy, only topical azoles are recommended.

Q: Which fungus possesses a capsule?

Cryptococcus. **Explanation:** The presence of a polysaccharide capsule is a defining characteristic of **Cryptococcus neoformans**, making it unique among clinically significant fungi. This capsule is primarily composed of **Glucuronoxylomannan (GXM)**, which acts as a potent virulence factor by inhibiting phagocytosis and suppressing T-cell responses. **Why Cryptococcus is correct:** * It is the only medically important fungus that is **encapsulated**. * The capsule does not stain with common dyes, creating a "halo" effect against a dark background in **India Ink** or Nigrosin preparations of CSF. * It can also be visualized using specific stains like **Mucicarmine** (stains the capsule red) or Alcian blue. **Why other options are incorrect:** * **Candida:** A budding yeast (with pseudohyphae) that lacks a polysaccharide capsule. Its primary virulence factors are biofilm formation and phenotypic switching. * **Aspergillus:** A filamentous fungus (mold) characterized by septate hyphae with acute-angle branching. It is non-encapsulated. * **Mucor:** A member of the Zygomycetes family, it presents as broad, non-septate hyphae with right-angle branching. It does not possess a capsule. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnosis:** The **Cryptococcal Antigen (CrAg)** test (Latex agglutination or LFA) is more sensitive than India Ink. * **Culture:** Grows on **Sabouraud Dextrose Agar (SDA)** as mucoid colonies; also grows on **Bird Seed Agar** (Niger seed agar) producing melanin (brown-black colonies) via phenoloxidase activity. * **Clinical:** Most common cause of fungal meningitis in HIV/AIDS patients (CD4 <100). * **Treatment:** Induction with Amphotericin B + Flucytosine, followed by Fluconazole.

Question 1

A 31-year-old HIV-positive man develops a severe pneumonia. Lower respiratory tract secretions obtained by fiberoptic bronchoscopy with bronchoalveolar lavage and stained with methenamine silver stain demonstrate cup-shaped cysts with sharply outlined walls. Which of the following organisms is the most likely pathogen in this case?

Accepted Answer

Pneumocystis jirovecii

Answer

Candida albicans

Answer

Giardia lamblia

Answer

Haemophilus influenzae

Question 2

A 25-year-old female complains of recurrent rhinitis, nasal discharge, and bilateral nasal blockage for one year. She has a history of asthma and allergies. On examination, multiple ethmoidal polyps are noted with mucosal thickening and impacted secretions in both nasal cavities. A biopsy is taken and cultured, showing growth of many hyphae and pseudohyphae with dichotomous branching typically at 45°. Which of the following is the most likely responsible organism?

Accepted Answer

Aspergillus fumigatus

Answer

Rhizopus

Answer

Mucor

Answer

Candida

Question 3

A 6-year-old girl presents with scaly patches on the scalp. Initial diagnostic smears and cultures were negative. Following a few weeks, she developed inflammatory lesions. Examination revealed hair that fluoresced under Wood's light, and subsequent smears showed septate hyphae. The family owns several pets. Which of the following is the most likely causative agent?

Accepted Answer

Microsporum canis

Answer

Microsporum audouinii

Answer

Trichophyton rubrum

Answer

Epidermophyton floccosum

Question 4

What is the most common fungal infection in febrile neutropenia?

Accepted Answer

Candida

Answer

Aspergillus niger

Answer

Mucormycosis

Answer

Aspergillus fumigatus

Question 5

Which of the following dermatophytes is spread from animals to humans?

Accepted Answer

Trichophyton verrucosum

Answer

Trichophyton rubrum

Answer

Trichophyton tonsurans

Answer

Trichophyton floccosum

Question 6

Which of the following is NOT true about Cryptococcus neoformans?

Accepted Answer

It produces a germ tube.

Answer

It is a yeast.

Answer

It is capsulated.

Answer

It can cause meningitis.

Question 7

What is the drug of choice for paracoccidioidomycosis?

Accepted Answer

Amphotericin B

Answer

Nystatin

Answer

Fluconazole

Answer

Ketoconazole

Question 8

A patient who recently underwent denture fixation presents with oral thrush that bleeds on scraping. What is the causative agent for this condition?

Accepted Answer

Candida

Answer

Diphtheria

Answer

Strep Mutans

Answer

Staph Aureus

Question 9

A 50-year-old diabetic female presents with intense pruritus and discharge from the vagina. A smear of the discharge shows budding yeast cells. What is the most likely causative agent?

Accepted Answer

Candida albicans

Answer

Trichomonas vaginalis

Answer

Mobiluncus

Answer

Chlamydia trachomatis

Question 10

Which fungus possesses a capsule?

Accepted Answer

Cryptococcus

Answer

Candida

Answer

Aspergillus

Answer

Mucor

Mycology — MCQs

Mycology — MCQs

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