Mycology Practice Questions

Q: Which of the following organisms cannot be cultured?

Pneumocystis jiroveci. **Explanation:** The correct answer is **Pneumocystis jiroveci**. **1. Why Pneumocystis jiroveci is correct:** *Pneumocystis jiroveci* (formerly *P. carinii*) is an atypical fungus that lacks ergosterol in its cell membrane. It is considered **obligate to the human host** and, despite numerous attempts, **cannot be grown in routine laboratory culture media** (axenic culture). Diagnosis relies heavily on microscopic visualization using special stains (Gomori Methenamine Silver or Direct Fluorescent Antibody) from clinical samples like Bronchoalveolar Lavage (BAL). **2. Why the other options are incorrect:** * **Klebsiella rhinoscleromatis (Option A):** This is a subspecies of *K. pneumoniae* that causes Rhinoscleroma (chronic granulomatous infection of the nose). It **can be cultured** on standard media like Blood Agar or MacConkey agar, appearing as large, mucoid colonies. * **Klebsiella ozaenae (Option B):** Associated with atrophic rhinitis (ozena), this organism is also **culturable** on routine laboratory media. * **Klebsiella granulomatis (Option C):** Formerly known as *Calymmatobacterium granulomatis*, it causes Granuloma Inguinale (Donovanosis). While it is **difficult to culture** and does not grow on routine agar, it can be grown in **yolk sacs of embryonated eggs** or specialized co-culture systems. In clinical practice, it is diagnosed by identifying "Donovan bodies" in tissue smears. **Clinical Pearls for NEET-PG:** * **Non-culturable organisms (High-Yield):** *Mycobacterium leprae*, *Treponema pallidum*, and *Pneumocystis jiroveci*. * **Pneumocystis prophylaxis:** Indicated in HIV patients when CD4 count falls below **200 cells/mm³**. Drug of choice: **TMP-SMX**. * **Stain of choice:** Gomori Methenamine Silver (GMS) shows "crushed ping-pong ball" appearance of cysts.

Q: Which of the following is NOT a cause of Madura foot?

Mucor. **Explanation:** **Madura foot (Mycetoma)** is a chronic, granulomatous, subcutaneous infection characterized by a clinical triad of **localized swelling, multiple interconnecting sinus tracts, and the discharge of grains.** It is caused by two distinct groups of organisms: **Eumycetoma** (fungal) and **Actinomycetoma** (filamentous bacteria). **Why Mucor is the correct answer:** **Mucor** is a member of the Zygomycetes family and causes **Mucormycosis**, an acute, aggressive, angioinvasive infection typically seen in immunocompromised patients or those with uncontrolled diabetes. It does not cause chronic granulomatous mycetoma or produce grains. **Analysis of other options:** * **Pseudallescheria boydii:** This is the most common cause of fungal mycetoma (**Eumycetoma**) worldwide. It typically produces white-to-yellow grains. * **Actinomycetes:** This is a broad group of filamentous, Gram-positive bacteria. **Actinomycetoma** accounts for the majority of cases in India (e.g., *Actinomadura madurae*). * **Nocardia:** Species like *Nocardia brasiliensis* are major causes of **Actinomycetoma**. They are partially acid-fast and produce fine, white-to-yellow grains. **High-Yield Clinical Pearls for NEET-PG:** * **The Grains:** The color of the grain can hint at the etiology. Black grains are always fungal (*Madurella mycetomatis*), while red grains are characteristic of *Actinomadura pelletieri*. * **Diagnosis:** The gold standard is the histopathological examination of the grain. * **Radiology:** The **"Dot-in-circle" sign** on MRI is a pathognomonic feature of mycetoma. * **Treatment:** Actinomycetoma responds well to antibiotics (Welsh regimen: Amikacin + Cotrimoxazole), whereas Eumycetoma often requires long-term antifungals (Itraconazole) and surgical debridement.

Q: A 40-year-old man presented with swelling over his foot with multiple sinus discharge. What is the likely diagnosis?

Madura mycosis. ***Madura mycosis*** - **Foot swelling** with **multiple sinus discharge** forms the classic triad of **mycetoma** (Madura foot), caused by fungal (**eumycetoma**) or bacterial (**actinomycetoma**) organisms. - The discharge typically contains **colored granules** (black for **Madurella mycetomatis**, white/yellow for **Nocardia** species) which are pathognomonic for this condition. *Acute myelitis* - Refers to **spinal cord inflammation** causing neurological deficits like **paraplegia** or **quadriplegia**, not foot swelling. - Presents with **motor weakness**, **sensory loss**, and **bladder dysfunction**, none of which match this clinical picture. *Chronic Osteomyelitis* - Typically presents with **single draining sinus** rather than multiple sinuses, and lacks the characteristic **granule discharge**. - More commonly affects **long bones** and is associated with **systemic symptoms** like fever and elevated inflammatory markers. *Dracunculosis* - Caused by **Dracunculus medinensis** (Guinea worm) presenting as a **single blister** with protruding worm, not multiple sinuses. - Endemic to specific regions in **Africa** and involves **contaminated water** consumption, with the worm emerging through skin after one year.

Q: Cigar-shaped yeast cells are seen with which of the following organisms?

S. schenkii. **Explanation:** The correct answer is **B. S. schenkii**. *Sporothrix schenckii* is a **dimorphic fungus**, meaning it exists as a mold in the environment (at 25°C) and as a yeast in human tissue (at 37°C). The characteristic morphological feature of the yeast phase in tissue or culture is the presence of **"cigar-shaped"** (elongated, fusiform) budding cells. This is a classic high-yield microscopic finding used to identify Sporotrichosis, often clinically associated with "Rose gardener’s disease." **Why the other options are incorrect:** * **C. albicans:** Typically presents as oval budding yeast cells with **pseudohyphae** and the ability to form true hyphae (germ tubes). * **H. capsulatum:** Appears as small, oval, **intracellular** yeast cells (often found within macrophages). They are not elongated or cigar-shaped. * **C. neoformans:** Characterized by round-to-oval yeast cells surrounded by a thick, **polysaccharide capsule**, best visualized with India Ink (negative staining). **High-Yield Clinical Pearls for NEET-PG:** 1. **Asteroid Bodies:** In tissue sections, *S. schenckii* may show a central yeast cell surrounded by eosinophilic radiating processes (Splendore-Hoeppli phenomenon). 2. **Clinical Presentation:** Typically presents as a linear chain of nodules following lymphatic drainage (**lymphocutaneous spread**) after traumatic inoculation (e.g., thorn prick). 3. **Drug of Choice:** **Itraconazole** is the preferred treatment. Historically, saturated solution of potassium iodide (SSKI) was used. 4. **Culture:** At 25°C, it produces "flowerette" or **daisy-like** arrangements of conidia.

Q: A man developed a pustule after being pricked by a thorn in the garden. Laboratory examination of the tissue specimen shows cigar-shaped budding yeasts. What is the most probable causative agent?

Sporothrix. **Explanation:** The clinical presentation and laboratory findings are classic for **Sporotrichosis**, caused by the dimorphic fungus **_Sporothrix schenckii_**. **1. Why the correct answer is right:** * **Mechanism of Injury:** The history of a "thorn prick" while gardening is a high-yield clinical clue for **Rose Gardener’s Disease**. The fungus is commonly found in soil, moss, and decaying vegetation. * **Morphology:** _Sporothrix_ is a **thermally dimorphic fungus**. In the tissue (at 37°C), it exists as yeast. The description of **"cigar-shaped" budding yeasts** is the pathognomonic histological feature for this organism. * **Clinical Progression:** It typically begins as a painless pustule or nodule at the site of inoculation, which may later ulcerate and spread along the draining lymphatics (nodular lymphangitis). **2. Why the incorrect options are wrong:** * **B. Sporotrichosis:** This is the name of the **disease**, not the causative agent. The question asks for the "causative agent," making _Sporothrix_ the more precise answer. * **C. Phialophora:** This is a genus of dematiaceous (pigmented) fungi that causes **Chromoblastomycosis**. Histology would show "copper-colored" sclerotic bodies (Medlar bodies), not cigar-shaped yeasts. * **D. Aspergillus:** This is a monomorphic mold characterized by septate hyphae with **acute-angle (45°) branching**. It does not form yeasts in tissue. **High-Yield Clinical Pearls for NEET-PG:** * **Asteroid Bodies:** In tissue, yeasts may be surrounded by eosinophilic material (Splendore-Hoeppli phenomenon), known as Asteroid bodies. * **Culture:** At 25°C, it grows as a mold with "flowerette" or "daisy-like" arrangements of conidia. * **Treatment:** The drug of choice is **Itraconazole**. Historically, saturated solution of potassium iodide (SSKI) was used.

Q: Penicillium marneffei is commonly associated with which of the following conditions?

Acquired Immunodeficiency Syndrome (AIDS). **Explanation:** *Penicillium marneffei* (now reclassified as ***Talaromyces marneffei***) is a unique **dimorphic fungus** that serves as a major opportunistic pathogen and a defining illness in patients with **Acquired Immunodeficiency Syndrome (AIDS)**, particularly in Southeast Asia (endemic in Thailand, Vietnam, and Southern China). **1. Why Option B is Correct:** In patients with advanced HIV/AIDS (typically with **CD4 counts <100 cells/μL**), *T. marneffei* causes a systemic infection involving the reticuloendothelial system. It is characterized by fever, weight loss, anemia, and distinctive **umbilicated skin lesions** (resembling *Molluscum contagiosum*). The fungus is intracellular, often seen within macrophages, mimicking *Histoplasma capsulatum*. **2. Why Other Options are Incorrect:** * **A. Tuberculosis:** While TB is the most common opportunistic infection in HIV, *T. marneffei* is a fungal pathogen, not a mycobacterial one. They may co-exist, but the fungus is not "associated" with TB itself. * **C. Diabetes Mellitus:** DM is strongly associated with **Mucormycosis** (Zygomycosis) and *Candida* infections, but not specifically with *T. marneffei*. * **D. Kala-azar:** Caused by *Leishmania donovani*, it presents with similar hepatosplenomegaly, but it is a protozoal disease. **Clinical Pearls for NEET-PG:** * **Dimorphism:** It is the only *Penicillium* species that is thermally dimorphic (Mould at 25°C; Yeast at 37°C). * **Laboratory Hallmark:** On Sabouraud Dextrose Agar (SDA) at 25°C, it produces a characteristic **diffusible red pigment**. * **Microscopy:** Yeast cells divide by **fission** (transverse septum), not budding. * **Treatment:** Intravenous Amphotericin B followed by oral Itraconazole.

Q: Pneumocystis jirovecii causes infection primarily in which species?

Rats. **Explanation:** The nomenclature of *Pneumocystis* species is strictly host-specific. While the genus was once thought to contain a single species (*P. carinii*), molecular analysis has proven that each mammalian host is infected by a distinct, genetically unique species of *Pneumocystis* that cannot cross-infect other species. * **Correct Option (A) Rats:** *Pneumocystis carinii* is the specific species that infects rats. Historically, all *Pneumocystis* organisms were referred to as *P. carinii*. However, current taxonomy restricts the name ***P. carinii*** (and *P. wakefieldiae*) specifically to the species found in **rats**. * **Incorrect Option (C) Humans:** The species that causes human infection (Pneumocystis Pneumonia - PCP) is **_Pneumocystis jirovecii_**. It is a common opportunistic infection in HIV/AIDS patients. * **Incorrect Options (B) & (D):** Mice are infected by *P. murina*, and rabbits are infected by *P. oryctolagi*. **High-Yield Clinical Pearls for NEET-PG:** 1. **Taxonomy Shift:** *Pneumocystis* was previously classified as a protozoan but is now classified as a **fungus** based on nucleic acid analysis (rRNA). 2. **Staining:** The gold standard for diagnosis is identifying cysts in bronchoalveolar lavage (BAL) fluid using **Gomori Methenamine Silver (GMS)** stain (appears as crushed ping-pong balls) or Direct Fluorescent Antibody (DFA) staining. 3. **Treatment:** Despite being a fungus, it does not respond to Ergosterol-inhibitors (like Amphotericin B) because it lacks ergosterol. The drug of choice is **Trimethoprim-Sulfamethoxazole (TMP-SMX)**. 4. **Prophylaxis:** Indicated in HIV patients when the **CD4 count falls below 200 cells/mm³**.

Q: An 18-year-old white male high-school student presents with a diffuse, painful rash on his thighs extending to his navel. He reports using topical hydrocortisone from a teammate for a previous groin rash. A KOH scraping of the current lesion shows hyaline hyphae. A schematic of the microscopic observation of the culture is provided. What is the most likely etiology?

Epidermophyton floccosum. ***Epidermophyton floccosum*** - Produces characteristic **club-shaped macroconidia in clusters** with **NO microconidia**, which matches the microscopic culture morphology described. - Commonly causes **tinea cruris** (jock itch) that can spread to thighs and abdomen, especially when topical steroids are inappropriately used causing **tinea incognito**. *Microsporum canis* - Produces **spindle-shaped macroconidia** with **rough, thick walls** and **microconidia**, unlike the described morphology. - Typically causes **tinea capitis** and **tinea corporis** in children, often acquired from infected cats or dogs. *Trichophyton rubrum* - Shows **pencil-shaped macroconidia** and **abundant microconidia** on microscopy, different from the club-shaped pattern. - More commonly causes **chronic tinea pedis** and **onychomycosis** rather than acute groin infections. *Trichophyton tonsurans* - Produces **balloon-shaped microconidia** and few macroconidia, contrasting with the described morphology. - Primarily causes **tinea capitis** in children and is the most common cause of scalp ringworm in the United States.

Q: Which of the following is NOT an 'all except' characteristic of acute pseudomembranous candidiasis?

May be associated with denture stomatitis. **Explanation:** Acute Pseudomembranous Candidiasis, commonly known as **Oral Thrush**, is the most classic presentation of *Candida albicans* infection. The core concept to understand here is the classification of oral candidiasis into **Acute** and **Chronic** forms. **Why Option C is the correct answer:** Denture stomatitis is a form of **Chronic Atrophic Candidiasis** (also known as Chronic Erythematous Candidiasis). It is characterized by localized chronic erythema and edema of the mucosa covered by a denture. It is not a feature of the "Acute Pseudomembranous" type, which is defined by removable white plaques rather than chronic tissue changes under a prosthetic. **Analysis of Incorrect Options:** * **Option A (Oral Thrush):** This is the clinical synonym for acute pseudomembranous candidiasis. It presents as creamy white, "curd-like" patches on the tongue and buccal mucosa. * **Option B (Immunocompromised patients):** This is a hallmark characteristic. It is frequently seen in patients with HIV/AIDS (where it is an AIDS-defining illness), leukemia, or those undergoing chemotherapy. * **Option D (Systemic corticosteroids):** Prolonged use of systemic steroids or broad-spectrum antibiotics alters the oral flora and suppresses local immunity, acting as a major predisposing factor for the acute pseudomembranous form. **NEET-PG High-Yield Pearls:** * **The "Scrape Test":** The white pseudomembrane in thrush **can be scraped off** with a tongue depressor, leaving behind an erythematous or bleeding base. This distinguishes it from Oral Leukoplakia (which cannot be scraped off). * **Diagnosis:** Primarily clinical, but confirmed by KOH mount showing budding yeast cells and **pseudohyphae**. * **Treatment:** Topical Nystatin or Clotrimazole for mild cases; oral Fluconazole for moderate-to-severe or systemic cases.

Question 1

Which of the following organisms cannot be cultured?

Accepted Answer

Pneumocystis jiroveci

Answer

Klebsiella rhinoscleromatis

Answer

Klebsiella ozaenae

Answer

Klebsiella granulomatis

Question 2

A 38-year-old AIDS patient presents with a one-week history of fever and increasing headache. He also reports photophobia, nausea, and weakness. His past medical history is significant for Pneumocystis pneumonia, and his CD4 count is 89. Current medications include trimethoprim/sulfamethoxazole and indinavir. Cerebrospinal fluid (CSF) analysis reveals 4 WBCs, and budding encapsulated yeast forms grow on Sabouraud's agar. What is the accurate description of the morphology of the infectious form of the organism responsible for this patient's illness?

Accepted Answer

Encapsulated budding yeasts

Answer

Broad-based, budding yeasts

Answer

Budding yeasts in a pseudohyphae

Answer

Cylindrical arthroconidia

Question 3

Which of the following is NOT a cause of Madura foot?

Accepted Answer

Mucor

Answer

Pseudallescheria

Answer

Actinomycetes

Answer

Nocardia

Question 4

A 40-year-old man presented with swelling over his foot with multiple sinus discharge. What is the likely diagnosis?

Accepted Answer

Madura mycosis

Answer

Acute myelitis

Answer

Chronic Osteomyelitis

Answer

Dracunculosis

Question 5

Cigar-shaped yeast cells are seen with which of the following organisms?

Accepted Answer

S. schenkii

Answer

C. albicans

Answer

H. capsulatum

Answer

C. neoformans

Question 6

A man developed a pustule after being pricked by a thorn in the garden. Laboratory examination of the tissue specimen shows cigar-shaped budding yeasts. What is the most probable causative agent?

Accepted Answer

Sporothrix

Answer

Sporotrichosis

Answer

Phialophora

Answer

Aspergillus

Question 7

Penicillium marneffei is commonly associated with which of the following conditions?

Accepted Answer

Acquired Immunodeficiency Syndrome (AIDS)

Answer

Tuberculosis

Answer

Diabetes Mellitus

Answer

Kala-azar

Question 8

Pneumocystis jirovecii causes infection primarily in which species?

Accepted Answer

Rats

Answer

Mice

Answer

Humans

Answer

Rabbits

Question 9

An 18-year-old white male high-school student presents with a diffuse, painful rash on his thighs extending to his navel. He reports using topical hydrocortisone from a teammate for a previous groin rash. A KOH scraping of the current lesion shows hyaline hyphae. A schematic of the microscopic observation of the culture is provided. What is the most likely etiology?

Accepted Answer

Epidermophyton floccosum

Answer

Microsporum canis

Answer

Trichophyton rubrum

Answer

Trichophyton tonsurans

Question 10

Which of the following is NOT an 'all except' characteristic of acute pseudomembranous candidiasis?

Accepted Answer

May be associated with denture stomatitis

Answer

Oral thrush

Answer

Commonly occurs in immunocompromised patients

Answer

Occurs in patients receiving systemic corticosteroid therapy

Mycology — MCQs

Mycology — MCQs

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