Mycology Practice Questions

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.

Q: Sporulation from flask-shaped, pigmented projections is commonly observed in which one of the following fungi?

P. verrucosa. **Explanation:** The question describes **Phialophora type of sporulation**, which is a diagnostic hallmark of **Phialophora verrucosa**, one of the primary causative agents of **Chromoblastomycosis**. 1. **Why P. verrucosa is correct:** In this fungus, conidia are produced from **phialides**. These are characteristic **flask-shaped or vase-shaped** pigmented projections (conidiogenous cells) that possess a distinct, darkened, cup-like collarette at the apex. The conidia are typically extruded in clusters from these openings, resembling a "bouquet of flowers" in a vase. 2. **Why the other options are incorrect:** * **E. floccosum (Epidermophyton):** A dermatophyte characterized by large, smooth-walled, **club-shaped (macroconidia)** arranged in pairs or triplets. It lacks microconidia and flask-shaped phialides. * **C. immitis (Coccidioides):** A dimorphic fungus that forms **spherules** filled with endospores in tissue and **arthroconidia** (rectangular, barrel-shaped spores) in culture. * **M. canis (Microsporum):** A dermatophyte known for spindle-shaped, thick-walled macroconidia with **tapered, recurved (hooked) ends**. **High-Yield Clinical Pearls for NEET-PG:** * **Chromoblastomycosis:** A chronic subcutaneous mycosis characterized by "cauliflower-like" lesions. * **Sclerotic Bodies (Medlar Bodies):** The pathognomonic finding in histopathology—thick-walled, dark brown, copper-colored structures (resembling "copper pennies") that divide by septation, not budding. * **Other Sporulation Types in Chromoblastomycosis:** * *Cladosporium type:* Branching chains of conidia (Shield cells). * *Rhinocladiella type:* Conidia borne laterally and terminally on a conidiophore (Acrotheca type).

Question 1

What is the most common fungal infection in febrile neutropenia?

Accepted Answer

Candida

Answer

Aspergillus niger

Answer

Mucormycosis

Answer

Aspergillus fumigatus

Question 2

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 3

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 4

What is the drug of choice for paracoccidioidomycosis?

Accepted Answer

Amphotericin B

Answer

Nystatin

Answer

Fluconazole

Answer

Ketoconazole

Question 5

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 6

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 7

Which fungus possesses a capsule?

Accepted Answer

Cryptococcus

Answer

Candida

Answer

Aspergillus

Answer

Mucor

Question 8

Sporulation from flask-shaped, pigmented projections is commonly observed in which one of the following fungi?

Accepted Answer

P. verrucosa

Answer

E. floccosum

Answer

C. immitis

Answer

M. canis

Question 9

A patient, two months post-renal transplant, presents with difficulty in breathing. Chest X-ray reveals bilateral diffuse interstitial infiltrates, predominantly in the perihilar region. What is the most probable etiologic agent?

Accepted Answer

Pneumocystis jirovecii

Answer

Cytomegalovirus (CMV)

Answer

Mycobacterium tuberculosis

Answer

Staphylococcus aureus

Question 10

A 26-year-old male presents with a circular, itchy, inflamed, slightly raised skin lesion. He reports his pet dog sleeps with him and has localized areas of hair loss. The patient has no other symptoms. What would be expected on a KOH preparation of skin scrapings?

Accepted Answer

Hyphae with little branching, possibly breaking up into arthroconidia

Answer

Clusters of yeast-like cells and short, curved, septate hyphae

Answer

Filariform larvae

Answer

Budding yeasts with some pseudohyphae and true hyphae

Mycology — MCQs

Mycology — MCQs

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