Mycology Practice Questions

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.

Q: Black coloured hard nodules in hair are produced by which organism?

Piedraia hortae. **Explanation:** The question describes the classic clinical presentation of **Black Piedra**, a superficial fungal infection of the hair shaft. **1. Why Piedraia hortae is correct:** *Piedraia hortae* is a dematiaceous (pigmented) fungus that causes **Black Piedra**. It produces **hard, black, gritty nodules** that are firmly attached to the hair shaft, primarily on the scalp. Under microscopy, these nodules consist of a dense mass of hyphae and contain asci with ascospores. **2. Why the other options are incorrect:** * **Epidermophyton floccosum:** This is a dermatophyte that causes Tinea infections (like Tinea cruris or pedis). It involves the skin and nails but does not form hard nodules on the hair shaft. * **Hortaea werneckii:** This fungus causes **Tinea nigra**, which presents as painless, brown-to-black macules on the **palms and soles**, not as hair nodules. * **Malassezia furfur:** This yeast causes **Pityriasis versicolor** (hypo/hyperpigmented scaly patches) and Seborrheic dermatitis. It does not produce hard nodules on hair. **3. High-Yield Clinical Pearls for NEET-PG:** * **Black Piedra vs. White Piedra:** While *Piedraia hortae* causes Black Piedra (hard, black nodules), **Trichosporon beigelii** causes **White Piedra** (soft, white-to-light brown nodules, usually on axillary or pubic hair). * **Tinea Nigra Diagnosis:** Look for "2-streamed" or branched septate hyphae and arthroconidia on KOH mount. * **Pityriasis Versicolor Diagnosis:** Characterized by the "Spaghetti and Meatball" appearance (short curved hyphae and yeast cells) on KOH mount. * **Wood’s Lamp:** *Malassezia furfur* shows a characteristic golden-yellow fluorescence.

Q: A 28-year-old HIV-positive male complains of pain on swallowing. Physical examination is remarkable for white plaque-like material on his tongue and buccal mucosa, which is scraped and sent to the laboratory. Based on these findings and the laboratory results, the man is diagnosed with acquired immunodeficiency syndrome (AIDS). With which of the following agents is the man most likely infected?

Candida albicans. **Explanation:** The clinical presentation of white, plaque-like material on the tongue and buccal mucosa that can be scraped off is classic for **Oral Candidiasis (Thrush)**. In an HIV-positive patient, the progression from oral involvement to painful swallowing (odynophagia) indicates **Esophageal Candidiasis**, which is an **AIDS-defining illness**. **Why Candida albicans is correct:** * **Clinical Presentation:** It presents as creamy white curd-like patches (pseudomembranes) that, when scraped, may leave an erythematous or bleeding base. * **Microscopy:** Laboratory findings typically show budding yeast cells and **pseudohyphae**. It is the most common opportunistic fungal infection in HIV patients. * **Significance:** While oral thrush can occur at CD4 counts <500 cells/mm³, esophageal involvement usually signifies a CD4 count **<200 cells/mm³**, marking the transition to AIDS. **Why other options are incorrect:** * **Cytomegalovirus (CMV):** While CMV can cause esophagitis in AIDS patients (CD4 <50), it typically presents with **large, shallow linear ulcers**, not white plaques. * **Herpes simplex I (HSV-1):** HSV esophagitis presents with small, deep **"punched-out" ulcers** and characteristic Cowdry type A inclusion bodies, not scrapable plaques. * **Human herpesvirus 8 (HHV-8):** This is the causative agent of **Kaposi Sarcoma**, which presents as reddish-purple macules or nodules, not white plaques. **High-Yield Clinical Pearls for NEET-PG:** * **Germ Tube Test:** Positive for *C. albicans* (formation of true hyphae from yeast cells in serum at 37°C). * **Culture:** Grows on Sabouraud Dextrose Agar (SDA) as creamy white colonies. * **Treatment:** Oral Fluconazole is the first-line treatment for esophageal candidiasis; Nystatin "swish and swallow" is used for mild oral thrush.

Q: Which type of candidiasis is associated with leukoplakia?

Chronic hyperplastic candidiasis. **Explanation:** **Chronic Hyperplastic Candidiasis (CHC)**, also known as **Candidal Leukoplakia**, is the correct answer because it is the only clinical variant of oral candidiasis that presents as a persistent, white, keratotic plaque. Unlike other forms, these lesions are **non-scrapable** and are histologically characterized by fungal hyphae invading the superficial layers of the oral epithelium, leading to significant hyperplasia. It is considered a premalignant condition, as a small percentage of cases can progress to squamous cell carcinoma. **Analysis of Incorrect Options:** * **Acute Pseudomembranous Candidiasis (Thrush):** Presents as creamy white "curd-like" patches. The defining feature is that these patches **can be scraped off**, leaving an erythematous (bleeding) base. * **Acute Atrophic Candidiasis:** Often associated with broad-spectrum antibiotic use; it presents as a painful, red, "burning" tongue rather than a white plaque. * **Chronic Atrophic Candidiasis (Denture Stomatitis):** Commonly seen under ill-fitting dentures. It is characterized by localized erythema and inflammation of the denture-bearing mucosa, not leukoplakia. **High-Yield Clinical Pearls for NEET-PG:** * **Scrapability:** If the white lesion scrapes off, think **Thrush**; if it does not, think **Leukoplakia/CHC**. * **Risk Factors:** Smoking is a major predisposing factor for the hyperplastic variant. * **Diagnosis:** Periodic Acid-Schiff (PAS) stain is the gold standard to demonstrate fungal hyphae in tissue sections. * **Management:** CHC requires long-term antifungal therapy and regular follow-up due to its malignant potential.

Q: A patient self-diagnosed with athlete's foot (tinea pedis) used an over-the-counter product. While the condition improved, it did not fully resolve. A dermatologist was consulted, and a skin scraping was sent for fungal culture. The culture yielded a slow-growing colony that produced a few small microconidia. This finding is consistent with the isolation of a dermatophyte from which genera?

Trichophyton. **Explanation:** The clinical presentation of **tinea pedis** (athlete's foot) and the laboratory findings point directly to the genus **Trichophyton**. 1. **Why Trichophyton is correct:** Dermatophytes are classified into three genera based on their macroconidia and microconidia. *Trichophyton* species (like *T. rubrum*, the most common cause of tinea pedis) are characterized by **abundant microconidia** and **rare, smooth-walled, pencil-shaped macroconidia**. In many cultures, they grow slowly and may only produce a few small microconidia, fitting the description in the question. 2. **Why the other options are incorrect:** * **Microsporum:** These are characterized by **abundant, thick-walled, spindle-shaped macroconidia** with rough surfaces. Microconidia are usually scarce. * **Epidermophyton:** This genus (specifically *E. floccosum*) produces **club-shaped macroconidia** in clusters and is unique because it **never produces microconidia**. * **Trichosporon:** This is a yeast-like fungus responsible for White Piedra. It produces arthroconidia and blastoconidia, not the typical micro/macroconidia structure of dermatophytes. **High-Yield NEET-PG Pearls:** * **Tinea Pedis:** Most commonly caused by *Trichophyton rubrum* (distal subungual) and *Trichophyton mentagrophytes*. * **Macroconidia Mnemonic:** * **M**icrosporum = **M**any (and spindle-shaped). * **T**richophyton = **T**enous (few/rare and pencil-shaped). * **E**pidermophyton = **E**mpty of microconidia (only club-shaped macroconidia). * **Wood’s Lamp:** *Microsporum* species fluoresce (bright green), while most *Trichophyton* species (except *T. schoenleinii*) do not.

Q: Which of the following is not a fungal infection?

Rhinosporidiosis. **Explanation:** The correct answer is **Rhinosporidiosis**. Historically, *Rhinosporidium seeberi* was classified as a fungus due to its morphology (presence of sporangia and spores). However, modern molecular phylogenetic analysis has reclassified it as a **Mesomycetozoean**, a group of aquatic protists (parasites) located at the evolutionary boundary between animals and fungi. It primarily causes chronic granulomatous lesions, typically presenting as friable, leafy, strawberry-like polyps in the nasal cavity. **Analysis of Incorrect Options:** * **Sporotrichosis:** Caused by the dimorphic fungus *Sporothrix schenckii*. It is often called "Rose gardener’s disease" and typically presents with lymphocutaneous nodules. * **Torulosis:** This is an archaic synonym for **Cryptococcosis**, caused by the encapsulated yeast *Cryptococcus neoformans*. It is a major cause of fungal meningitis in immunocompromised patients. * **Candidiasis:** Caused by *Candida* species (most commonly *C. albicans*), which are opportunistic yeast-like fungi responsible for conditions ranging from oral thrush to systemic candidemia. **High-Yield Clinical Pearls for NEET-PG:** * **Rhinosporidiosis:** Look for a history of bathing in stagnant water. The characteristic histopathology shows large **sporangia** (up to 350 µm) containing thousands of **endospores**. It cannot be cultured on artificial media. * **Treatment of choice:** Surgical excision with electrocautery of the base. * **Differential Diagnosis:** Do not confuse Rhinosporidiosis with *Coccidioidomycosis*; both show endosporulating spherules, but *Coccidioides* spherules are much smaller (up to 60 µm).

Q: All statements are true about mycetoma except:

Eumycetoma is caused by bacteria. **Explanation:** The correct answer is **A**. Mycetoma is a chronic, granulomatous, subcutaneous infection characterized by a triad of localized swelling, underlying bone destruction, and the presence of discharging sinuses containing grains. It is classified into two types based on the causative agent: 1. **Eumycetoma:** Caused by **fungi** (e.g., *Madurella mycetomatis*). 2. **Actinomycetoma:** Caused by **filamentous bacteria** (e.g., *Nocardia*, *Actinomadura*). Therefore, the statement that Eumycetoma is caused by bacteria is false. **Analysis of other options:** * **Option B:** Surgery is often necessary for Eumycetoma, as fungal cases respond poorly to medical therapy alone. Wide local excision or amputation may be required. In contrast, Actinomycetoma is primarily managed with antibiotics (Welsh regimen). * **Option C:** Mycetoma is typically a **painless** lesion despite significant swelling and deformity. Pain usually only occurs with secondary bacterial infection or deep bone involvement. * **Option D:** Diagnosis is clinically suspected by the presence of the triad and confirmed by examining the **grains** (sulfur granules) discharged from the sinuses. The color, size, and consistency of these grains provide clues to the specific causative agent. **NEET-PG High-Yield Pearls:** * **Madura Foot:** The common clinical name for mycetoma. * **Grains:** Black grains are pathognomonic for **fungal** (Eumycetoma) etiology. * **Welsh Regimen:** The gold standard treatment for Actinomycetoma (Amikacin + Cotrimoxazole). * **Radiology:** "Dot-in-circle" sign on MRI is a highly specific diagnostic feature.

Question 1

Pneumocystis jirovecii causes infection primarily in which species?

Accepted Answer

Rats

Answer

Mice

Answer

Humans

Answer

Rabbits

Question 2

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 3

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

Question 4

Black coloured hard nodules in hair are produced by which organism?

Accepted Answer

Piedraia hortae

Answer

Epidermophyton floccosum

Answer

Hortaea werneckii

Answer

Malassezia furfur

Question 5

A 28-year-old HIV-positive male complains of pain on swallowing. Physical examination is remarkable for white plaque-like material on his tongue and buccal mucosa, which is scraped and sent to the laboratory. Based on these findings and the laboratory results, the man is diagnosed with acquired immunodeficiency syndrome (AIDS). With which of the following agents is the man most likely infected?

Accepted Answer

Candida albicans

Answer

Cytomegalovirus

Answer

Herpes simplex I

Answer

Human herpesvirus 8

Question 6

Which fungus cannot be grown on artificial media?

Accepted Answer

Rhinosporidium seeberi

Answer

Penicillium marneffei

Answer

Aspergillus flavus

Answer

Sporothrix schenckii

Question 7

Which type of candidiasis is associated with leukoplakia?

Accepted Answer

Chronic hyperplastic candidiasis

Answer

Acute pseudomembranous candidiasis

Answer

Acute atrophic candidiasis

Answer

Chronic atrophic candidiasis

Question 8

A patient self-diagnosed with athlete's foot (tinea pedis) used an over-the-counter product. While the condition improved, it did not fully resolve. A dermatologist was consulted, and a skin scraping was sent for fungal culture. The culture yielded a slow-growing colony that produced a few small microconidia. This finding is consistent with the isolation of a dermatophyte from which genera?

Accepted Answer

Trichophyton

Answer

Microsporum

Answer

Epidermophyton

Answer

Trichosporon

Question 9

Which of the following is not a fungal infection?

Accepted Answer

Rhinosporidiosis

Answer

Sporotrichosis

Answer

Torulosis

Answer

Candidiasis

Question 10

All statements are true about mycetoma except:

Accepted Answer

Eumycetoma is caused by bacteria

Answer

Surgery is an important component of treatment

Answer

It is usually painless

Answer

Diagnosis can be made by examination of the lesion

Mycology — MCQs

Mycology — MCQs

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