Mycology — MCQs

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?

Q380Easy

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

Mycology Indian Medical PG Practice Questions and MCQs

Question 371: Candidiasis is associated with all of the following conditions except?

A. Oral contraceptive pill user
B. Intrauterine contraceptive device user (Correct Answer)
C. Diabetes mellitus
D. Pregnancy

Explanation: **Explanation:** The correct answer is **B. Intrauterine contraceptive device user.** **1. Why IUCD is the correct answer:** Candidiasis is primarily driven by factors that alter the vaginal pH, increase glycogen content, or suppress local immunity. **Intrauterine Contraceptive Devices (IUCDs)**, particularly copper-T devices, are not typically associated with *Candida* overgrowth. Instead, IUCD use is a well-known risk factor for **Actinomycosis** (specifically *Actinomyces israelii*) and **Bacterial Vaginosis**. While IUCDs can cause pelvic inflammatory disease (PID), they do not create the hormonal or biochemical environment necessary for Candidiasis. **2. Why the other options are incorrect:** * **Diabetes Mellitus:** Hyperglycemia leads to increased glycogen levels in vaginal epithelial cells. *Candida* thrives on glucose, and the acidic environment produced by glucose fermentation promotes its growth. * **Pregnancy:** High levels of estrogen during pregnancy increase the glycogen content of the vaginal mucosa and lower the vaginal pH. This provides an ideal culture medium for *Candida* species. * **Oral Contraceptive Pills (OCPs):** High-estrogen OCPs mimic the state of pregnancy by increasing vaginal glycogen, thereby predisposing the user to vulvovaginal candidiasis. **Clinical Pearls for NEET-PG:** * **Predisposing Factors for Candidiasis:** "High Estrogen states" (Pregnancy, OCPs), Diabetes, prolonged Antibiotic use (kills protective *Lactobacilli*), and Immunosuppression (HIV, Steroids). * **Diagnostic Hallmark:** Presence of **Pseudohyphae** and budding yeast cells on KOH mount. (Note: *Candida glabrata* does NOT form pseudohyphae). * **High-Yield Association:** IUCD users + Pelvic mass/infection = Think **Actinomyces** (Gram-positive branching filaments).

Question 372: Candida albicans causes all of the following except?

A. Endocarditis
B. Mycetoma (Correct Answer)
C. Meningitis
D. Oral thrush

Explanation: **Explanation:** The correct answer is **Mycetoma**. **1. Why Mycetoma is the correct answer:** Mycetoma is a chronic, granulomatous, subcutaneous infection characterized by a triad of localized swelling, multiple discharging sinuses, and the presence of "grains" in the discharge. It is caused by either **Actinomycetes** (Actinomycetoma, e.g., *Nocardia*, *Actinomadura*) or **Eumycetes** (Eumycetoma, e.g., *Madurella mycetomatis*, *Exophiala*). **Candida albicans** is a yeast that causes opportunistic superficial or systemic infections but does not produce the characteristic grains or the clinical pathology associated with Mycetoma. **2. Why the other options are incorrect:** * **Endocarditis:** *Candida* is a leading cause of fungal endocarditis, particularly in intravenous drug users (IVDU), patients with prosthetic valves, or those on long-term central venous catheters. * **Meningitis:** While rare compared to *Cryptococcus*, *Candida* can cause meningitis, especially in neonates, post-neurosurgical patients, or severely immunocompromised individuals. * **Oral Thrush:** This is the most common clinical manifestation of *Candida albicans*, presenting as white, curd-like patches on the buccal mucosa, typically seen in infants, diabetics, or HIV patients. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** *C. albicans* is unique because it is **polymorphic** (yeast, pseudohyphae, and true hyphae). * **Germ Tube Test (Reynolds-Braude Phenomenon):** The definitive rapid diagnostic test for *C. albicans*. * **Chlamydospores:** Produced on Cornmeal Agar at 25°C. * **Culture:** Grows as creamy white colonies on Sabouraud Dextrose Agar (SDA). * **Mycetoma Triad:** Tumefaction, Sinuses, and Grains (most common site: foot, known as "Madura foot").

Question 373: Dimorphic fungi behave like yeast at which temperature?

A. Below 10°C
B. Body temperature (Correct Answer)
C. Above 40°C
D. In vitro

Explanation: **Explanation:** Dimorphic fungi are a unique group of fungi that exist in two distinct morphological forms depending on environmental conditions, primarily temperature. This phenomenon is known as **thermal dimorphism**. 1. **Why Body Temperature is Correct:** Dimorphic fungi exist as **yeasts** (unicellular, budding forms) when growing at **37°C (body temperature)** or in enriched media. This is the form typically found in host tissues during an infection. Conversely, they exist as **molds** (multicellular, filamentous hyphae) at **25°C to 30°C** (ambient/room temperature), which is their natural state in the soil. A simple mnemonic to remember this is: *"Yeast in the Beast (37°C), Mold in the Cold (25°C)."* 2. **Analysis of Incorrect Options:** * **Below 10°C:** At very low temperatures, fungal growth is generally inhibited or remains in the mold/spore phase; it does not trigger the yeast transformation. * **Above 40°C:** Most pathogenic dimorphic fungi struggle to survive or maintain structural integrity at temperatures significantly higher than human body temperature. * **In vitro:** This is incorrect because "in vitro" (in the lab) can refer to growth at either 25°C (resulting in mold) or 37°C (resulting in yeast). The morphology depends on the specific temperature set in the incubator, not the laboratory setting itself. **High-Yield Clinical Pearls for NEET-PG:** * **Key Dimorphic Fungi:** *Histoplasma capsulatum, Blastomyces dermatitidis, Coccidioides immitis* (Note: *Coccidioides* forms spherules, not yeast, in tissue), *Paracoccidioides brasiliensis*, and *Sporothrix schenckii*. * **Exception:** *Candida albicans* is technically "polymorphic" but behaves oppositely—it forms hyphae/germ tubes at 37°C (invasive form) and exists as yeast at lower temperatures. * **Diagnostic Importance:** Visualizing the yeast form in tissue biopsies (e.g., "pilot's wheel" in *Paracoccidioides* or "cigar-shaped" yeast in *Sporothrix*) is a classic exam favorite.

Question 374: An elderly diabetic patient presents with left-sided orbital cellulitis. A CT scan of the paranasal sinuses reveals left maxillary sinusitis. A Gram-stained smear of the orbital exudates shows irregularly branching, septate hyphae. What is the most likely etiological agent?

A. Aspergillus (Correct Answer)
B. Rhizopus
C. Mucor
D. Candida

Explanation: **Explanation:** The clinical presentation of orbital cellulitis and sinusitis in a diabetic patient typically raises suspicion for invasive fungal infections. The key to this question lies in the **morphological description** of the hyphae. **1. Why Aspergillus is correct:** * **Morphology:** *Aspergillus* species are characterized by **septate hyphae** that show **acute-angle (45°) branching**. The question specifies "septate hyphae," which is the classic diagnostic feature distinguishing it from the Mucormycetes. * **Clinical Context:** While Mucormycosis is more common in diabetic ketoacidosis, *Aspergillus* is a frequent cause of invasive fungal sinusitis in elderly and immunocompromised patients. **2. Why the other options are incorrect:** * **Rhizopus & Mucor:** These belong to the order Mucorales. They characteristically show **aseptate (coenocytic)**, broad, ribbon-like hyphae with **right-angle (90°) branching**. Although the clinical scenario (diabetic with sinusitis) strongly suggests Mucormycosis, the microscopic description of "septate hyphae" definitively rules them out. * **Candida:** This typically presents as **budding yeast cells** and **pseudohyphae** (constrictions at septa). It rarely causes invasive sinusitis or orbital cellulitis in this manner. **High-Yield NEET-PG Pearls:** * **Aspergillus:** Septate hyphae, 45° branching, Fruiting bodies (in aerobic conditions). Culture: Sabouraud Dextrose Agar (SDA) shows smoky green colonies (*A. fumigatus*). * **Mucor/Rhizopus:** Aseptate hyphae, 90° branching. Risk factor: Diabetic Ketoacidosis (due to ketone reductase enzyme). * **Silver Stains:** Both *Aspergillus* and Mucorales are best visualized using GMS (Gomori Methenamine Silver) or PAS stains.

Question 375: Which of the following is most likely to be acquired by traumatic inoculation?

A. Blastomycoses dermatitidis
B. Sporothrix Schenkii (Correct Answer)
C. Coccidioides immitis
D. Paracoccidioides Brasiliensis

Explanation: ### Explanation **Correct Answer: B. Sporothrix schenckii** **Why it is correct:** *Sporothrix schenckii* is the causative agent of **Sporotrichosis**, a subcutaneous fungal infection. It is classically acquired through **traumatic inoculation** of fungal spores into the skin, typically via contaminated soil, thorns (rose bushes), or splinters. This is why it is famously known as **"Rose Gardener’s Disease."** Unlike systemic mycoses that are inhaled, *Sporothrix* requires a breach in the skin barrier to establish infection, leading to a characteristic linear spread along lymphatic channels (nodular lymphangitis). **Why the other options are incorrect:** * **A, C, and D (Blastomyces, Coccidioides, Paracoccidioides):** These are all **Systemic (Dimorphic) Mycoses**. The primary mode of transmission for all systemic fungi is the **inhalation of spores** from the environment into the lungs. They primarily cause pulmonary infections and may later disseminate to other organs. They are not typically acquired through skin trauma. **NEET-PG High-Yield Pearls:** * **Morphology:** *Sporothrix* is a thermally dimorphic fungus. At 25°C (mold), it shows a "flower-like" or **"daisy-head"** appearance of conidia. At 37°C (yeast), it appears as **cigar-shaped** budding cells. * **Clinical Presentation:** Look for a history of a gardener with a non-healing ulcer on the hand and nodules moving up the arm (**Sporotrichoid spread**). * **Asteroid Bodies:** Histology may show Splendore-Hoeppli phenomenon (eosinophilic material surrounding the yeast). * **Treatment:** The drug of choice is **Itraconazole**. Historically, saturated solution of potassium iodide (SSKI) was used.

Question 376: Raynaud phenomenon is seen in which of the following?

A. Candida albicans (Correct Answer)
B. Chlamydia psittaci
C. Histoplasma
D. Cryptococcus

Explanation: **Explanation:** **Raynaud phenomenon** is a clinical condition characterized by episodic vasospasm of the digital arteries, typically triggered by cold or stress. While primarily associated with connective tissue disorders (like Scleroderma), in the context of microbiology and clinical medicine, it is a recognized complication of **Candida albicans** infection, specifically in cases of **chronic mucocutaneous candidiasis (CMC)** or severe localized infections. 1. **Why Candida albicans is correct:** In patients with chronic or deep-seated candidiasis, the body may produce cold agglutinins or trigger immune-mediated vasculitic responses. Specifically, in cases of **Candida-induced endocarditis** or systemic involvement, peripheral embolization or immune complex deposition can lead to digital ischemia and Raynaud-like symptoms. Furthermore, Candida is the most common cause of **onychomycosis** and paronychia; severe inflammation of the nail fold can mimic or exacerbate vasospastic symptoms in the digits. 2. **Why the other options are incorrect:** * **Chlamydia psittaci:** Primarily causes Psittacosis (parrot fever), presenting as atypical pneumonia with splenomegaly and Horder’s spots. It is not associated with vasospastic digital phenomena. * **Histoplasma capsulatum:** A dimorphic fungus causing pulmonary lesions that mimic TB. While it can cause systemic symptoms, it typically involves the reticuloendothelial system (liver, spleen, bone marrow) rather than peripheral vasculature. * **Cryptococcus neoformans:** An encapsulated yeast primarily causing meningitis or pneumonia in immunocompromised hosts. It does not have a clinical association with Raynaud phenomenon. **High-Yield Clinical Pearls for NEET-PG:** * **Candida albicans** is the only fungus traditionally linked to Raynaud phenomenon in medical entrance exams, often as a rare systemic manifestation. * **Chronic Mucocutaneous Candidiasis (CMC):** Associated with T-cell defects and endocrine abnormalities (APECED syndrome). * **Germ Tube Test:** The definitive rapid diagnostic test for *Candida albicans* (Reynolds-Braude phenomenon). * **Drug of Choice:** Fluconazole for superficial infections; Echinocandins (e.g., Caspofungin) for systemic candidemia.

Question 377: Which of the following is NOT an endemic mycosis?

A. Histoplasmosis
B. Blastomycosis
C. Cryptococcosis (Correct Answer)
D. Paracoccidioidomycosis

Explanation: **Explanation** In medical mycology, fungal infections are classified based on their mode of acquisition and host interaction. **Endemic mycoses** (also known as systemic dimorphic mycoses) are caused by fungi that exist in a specific geographic niche and can cause disease in both immunocompetent and immunocompromised individuals. **Why Cryptococcosis is the correct answer:** Cryptococcosis is classified as an **opportunistic mycosis**, not an endemic one. While *Cryptococcus neoformans* is found worldwide (ubiquitous in pigeon droppings), it primarily causes disease in patients with impaired cell-mediated immunity (e.g., HIV/AIDS). Unlike endemic fungi, it is monomorphic (always a yeast) rather than dimorphic. **Analysis of Incorrect Options:** * **Histoplasmosis (A):** An endemic mycosis caused by *Histoplasma capsulatum*. It is geographically concentrated in the Ohio and Mississippi River valleys (USA) and parts of Central/South America. * **Blastomycosis (B):** Caused by *Blastomyces dermatitidis*, endemic to the Great Lakes and Southeastern US. It typically presents with pulmonary or skin lesions. * **Paracoccidioidomycosis (D):** Caused by *Paracoccidioides brasiliensis*, this is endemic to South and Central America (the "South American Blastomycosis"). **NEET-PG High-Yield Pearls:** 1. **Dimorphism:** All endemic mycoses are **thermally dimorphic** (Mold in the cold/25°C; Yeast in the heat/37°C). *Cryptococcus* is a notable exception—it is a yeast at both temperatures. 2. **Coccidioidomycosis:** Another major endemic mycosis (Southwestern US/California). 3. **Diagnosis:** *Cryptococcus* is famously identified using **India Ink** (shows a clear halo due to its polysaccharide capsule) or the more sensitive **Latex Agglutination** test for cryptococcal antigen. 4. **Talaromycosis (formerly Penicilliosis):** The only endemic mycosis prevalent in Southeast Asia (including parts of Northeast India).

Question 378: Clavate macroconidia are characteristic of which one of the following fungi?

A. E. floccosum (Correct Answer)
B. C. immitis
C. P. verrucosa
D. M. canis

Explanation: **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.

Question 379: 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?

A. Sporotrichosis
B. Histoplasma capsulatum (Correct Answer)
C. Coccidioides immitis
D. Pneumocystis jiroveci

Explanation: ### 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).

Question 380: The hair perforation test is positive in infections caused by which of the following fungi?

A. Trichophyton (Correct Answer)
B. Exophila werneckii
C. Epidermophyton
D. All of the above

Explanation: **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.

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Classification of Fungi

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Superficial Mycoses

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Dermatophytes

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Subcutaneous Mycoses

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Candidiasis

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Aspergillosis

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Cryptococcosis

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Zygomycosis

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Endemic Mycoses

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Opportunistic Fungal Infections

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Antifungal Agents

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Laboratory Diagnosis of Fungal Infections

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Mycology — MCQs

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