Mycology Practice Questions

Q: Tinea cruris is caused by which of the following fungi?

Epidermophyton. ***Epidermophyton*** - **_Epidermophyton floccosum_** is one of the common dermatophytes responsible for causing **tinea cruris** (jock itch) and tinea pedis (athlete's foot). - **Note:** Tinea cruris can be caused by multiple dermatophytes including **_Trichophyton rubrum_** (most common), **_T. mentagrophytes_**, and **_E. floccosum_**. Among the options listed, Epidermophyton is the only dermatophyte that commonly causes tinea cruris. - Microscopic examination of skin scrapings shows **septate hyphae**, and it typically invades the stratum corneum but **not hair or nails**. *Trichosporon* - **_Trichosporon_** species cause **white piedra** (a fungal infection of the hair shaft) and can cause systemic infections in immunocompromised individuals. - It is **not a dermatophyte** and does not cause tinea cruris. *Microsporum* - **_Microsporum_** species are primarily associated with **tinea capitis** (ringworm of the scalp) and **tinea corporis** (ringworm of the body). - While Microsporum can occasionally involve skin in the groin region, it is **rarely implicated in classic tinea cruris** and is not considered a typical causative agent compared to Trichophyton or Epidermophyton species. *Candida* - **_Candida_** species (e.g., **_Candida albicans_**) cause candidiasis, which commonly presents as **intertrigo** in skin folds, oral thrush, or vaginal yeast infections. - While it can occur in the groin area (**candidal intertrigo**), it is **not a dermatophyte** and is distinctly different from tinea cruris, often presenting with **satellite lesions** and an intensely erythematous, macerated rash.

Q: What is the most probable point of entry for Aspergillus?

Lungs. ***Lungs*** - The inhalation of **Aspergillus spores** (conidia) is the most common route of entry, leading to various forms of aspergillosis, especially in immunocompromised individuals. - Spores are ubiquitous in the environment and are easily aerosolized, making airborne transmission to the respiratory tract highly probable. *Puncture wound* - While fungal infections can occur via puncture wounds, this is a less common route for **Aspergillus** compared to airborne inhalation. - Cutaneous aspergillosis from direct inoculation is rare and typically seen in cases of severe trauma or surgical contamination in immunocompromised patients. *Blood* - **Aspergillus** does not typically originate in the blood; fungemia is usually a result of dissemination from a primary site of infection, most commonly the lungs, rather than a primary entry point. - Direct intravenous introduction of spores is highly uncommon and usually associated with contaminated medical devices or drugs rather than a natural point of entry. *Gastrointestinal tract* - The **gastrointestinal tract** is not a primary route of entry for **Aspergillus** in immune-competent individuals due to protective mechanisms like gastric acid and gut microbiota. - While ingestion of spores can occur, systemic infection originating from the GI tract is rare and generally seen only in severely immunocompromised patients with mucosal barrier damage.

Q: P. carinii primarily causes infection in which of the following?

Rats. ***Correct: Rats*** - *Pneumocystis carinii* was initially identified as a distinct species primarily infecting **rats**. - This species is known to cause **pneumocystosis** in its specific host, the rat. - After taxonomic reclassification based on host specificity, the name *Pneumocystis carinii* was **retained for the rat-specific species**. *Incorrect: Mice* - While other *Pneumocystis* species can infect mice (e.g., *Pneumocystis murina*), *Pneumocystis carinii* specifically refers to the species found in **rats**. - The host specificity of *Pneumocystis* species is well-established, meaning each species typically infects only one host. *Incorrect: Humans* - Humans are primarily infected by ***Pneumocystis jirovecii***, which was formerly known as *Pneumocystis carinii* f. sp. *hominis*, highlighting its **human host specificity**. - *Pneumocystis jirovecii* causes **Pneumocystis pneumonia (PCP)**, especially in immunocompromised individuals. *Incorrect: Rabbits* - Rabbits are known to be infected by their own specific *Pneumocystis* species, *Pneumocystis oryctolagi*. - Infections in rabbits are typically asymptomatic, but can cause pneumonia in **immunocompromised** animals.

Q: Which of the following organisms plays an important role in the pathogenesis of "malt worker's lung"?

Aspergillus clavatus. ***Aspergillus clavatus*** - **Aspergillus clavatus** is the specific causative agent of **malt worker's lung**, a form of hypersensitivity pneumonitis (extrinsic allergic alveolitis) - It thrives in the **moist, warm conditions of germinating barley**, where malt workers are exposed to its spores during the malting process - This occupational exposure leads to an immunologic reaction in the lungs *Aspergillus fumigatus* - While *Aspergillus fumigatus* is a common cause of various aspergillosis syndromes (e.g., allergic bronchopulmonary aspergillosis, invasive aspergillosis), it is **not** typically associated with malt worker's lung - It is more broadly distributed in organic matter but not specifically linked to the malt industry in this context *Pseudomonas* - *Pseudomonas* species are **gram-negative bacteria**, often associated with nosocomial infections, cystic fibrosis, or chronic lung infections - They are **not fungi** and do not play a role in this specific allergic lung disease or hypersensitivity pneumonitis *Micropolyspora faeni* - *Micropolyspora faeni* (now reclassified as *Saccharopolyspora rectivirgula*) is the causative agent of **farmer's lung**, another type of hypersensitivity pneumonitis - It is found in **moldy hay**, not in malted barley, and therefore does not cause malt worker's lung

Q: Microscopy of a corneal ulcer shows branching septate hyphae. The probable diagnosis is

Aspergillus. ***Aspergillus*** - **Branching septate hyphae** observed on microscopy are characteristic of *Aspergillus* species, which are common causes of **fungal keratitis**, especially after ocular trauma or in immunocompromised individuals. - *Aspergillus* keratitis often presents as a **corneal ulcer** with distinct borders and satellite lesions, reflecting the invasive nature of the fungus. *Candida* - *Candida* species are typically observed as **yeast cells** that may form **pseudohyphae**, rather than true septate hyphae with dichotomous branching. - While *Candida* can cause keratitis, its microscopic appearance is distinct from the branching septate hyphae described. *Histoplasma* - *Histoplasma capsulatum* is a **dimorphic fungus** that primarily causes pulmonary infections and disseminated disease, particularly in immunocompromised patients. - It is typically seen as **small intracellular yeast forms** in macrophages, not as hyphae in corneal ulcers. *Mucormycosis* - **Mucorales** (e.g., *Mucor*, *Rhizopus*) cause **mucormycosis**, characterized by **broad, non-septate, ribbon-like hyphae** with irregular branching. - This morphology is distinctly different from the described **branching septate hyphae**, ruling out mucormycosis.

Q: Which of the following is the MOST COMMON fungal cause of Mucormycosis?

Rhizopus oryzae. ***Rhizopus oryzae*** - This is the **most common genus and species** responsible for mucormycosis infections in humans. - It belongs to the order **Mucorales**, which are characterized by broad, non-septate hyphae with a tendency to invade blood vessels. *Candida albicans* - This fungus is a common cause of **candidiasis**, which can manifest as thrush, vaginitis, or invasive candidemia. - It does not cause mucormycosis; its cellular morphology and disease presentation are distinct. *Aspergillus fumigatus* - This is the primary causative agent of **aspergillosis**, which can range from allergic reactions to invasive forms like chronic pulmonary aspergillosis or invasive aspergillosis. - While it can cause severe fungal infections, it is morphologically distinct (septate hyphae) and does not cause mucormycosis. *Cryptococcus neoformans* - This encapsulated yeast is best known for causing **cryptococcosis**, particularly **meningoencephalitis** in immunocompromised individuals. - Its disease presentation and microscopic features (yeast with budding, prominent capsule) are entirely different from those of Mucorales.

Q: Which organism is characterized by a wide polysaccharide capsule that appears as a clear halo around the yeast cell on India ink staining?

Cryptococcus neoformans. ***Cryptococcus neoformans*** - This encapsulated yeast produces a **thick polysaccharide capsule** that is the key diagnostic feature - On **India ink preparation**, the capsule appears as a **clear halo** around the yeast cell because the ink particles cannot penetrate the capsule - This is the classic microscopic identification method for **Cryptococcus neoformans** in **cerebrospinal fluid** and other clinical specimens - The capsule can also be visualized using **mucicarmine stain** (stains red) or **alcian blue** *Penicillium marneffei* - This dimorphic fungus shows **intracellular yeast forms** with characteristic **central septation** (dividing by fission) - Typically found within macrophages and does not produce a prominent capsule - The yeast forms are oval to elongated with a transverse septum *Blastomyces dermatitidis* - Characterized by **large, thick-walled yeast cells** (8-15 μm) with **broad-based budding** - The cell wall is thick and refractile but there is **no polysaccharide capsule** - Budding occurs with a wide attachment point between mother and daughter cells *Candida albicans* - Forms **budding yeast cells**, **pseudohyphae**, and **true hyphae** (germ tubes) - Does not produce a polysaccharide capsule - Identified by germ tube formation at 37°C in serum

Q: A patient, a resident of Himachal Pradesh, presented with a series of ulcers in a row on his right leg. The biopsy from the affected area was taken and cultured on Sabouraud's dextrose agar. What is the most likely causative organism?

Sporothrix schenckii. ***Sporothrix schenckii*** - The presentation of "ulcers in a row" on the leg is highly suggestive of **lymphocutaneous sporotrichosis**, a characteristic finding where the infection spreads via lymphatic drainage. - This fungus is endemic in certain regions including parts of **Himachal Pradesh**, and is typically acquired through contact with contaminated soil or plant material (e.g., rose thorns, sphagnum moss). - Grows well on **Sabouraud's dextrose agar**, producing characteristic colonies. *Cladosporium spp.* - While *Cladosporium* can cause **phaeohyphomycosis** or allergic fungal sinusitis, it does not typically present with the classic lymphocutaneous lesions described. - These fungi are common environmental contaminants and their infections are usually associated with chronic skin lesions, not a linear spread of ulcers. *Pseudoallescheria boydii* - *Pseudoallescheria boydii* is a common cause of **mycetoma** (Madura foot), characterized by chronic, destructive lesions with granulomas and sinus tracts that discharge grains. - This presentation is distinct from the linear ulcerative lesions described in the patient. *Nocardia brasiliensis* - *Nocardia brasiliensis* is a bacterium (an actinomycete) that causes **actinomycetoma**, characterized by chronic, suppurative lesions with sinus tracts discharging grains. - The characteristic **"ulcers in a row"** (lymphocutaneous spread pattern) is **not typical** of Nocardia infection, which presents as localized mycetoma rather than ascending lymphatic involvement. - While Nocardia can grow on some fungal media, the clinical presentation is the key distinguishing feature here.

Q: Pityriasis versicolor is caused by which organism?

M. furfur. ***M. furfur*** - **Pityriasis versicolor** is caused by **Malassezia furfur** (also known as Pityrosporum ovale), a dimorphic yeast that is a normal inhabitant of human skin. - Under certain conditions (e.g., humidity, excessive sweating), it overgrows, leading to characteristic hypopigmented or hyperpigmented patches. *E. floccosum* - **Epidermophyton floccosum** is a dermatophyte known to cause **tinea pedis (athlete's foot)**, tinea cruris (jock itch), and tinea unguium (nail infections). - It does not cause pityriasis versicolor, which is a superficial yeast infection, not a dermatophyte infection. *M. gypseum* - **Microsporum gypseum** is a geophilic dermatophyte, meaning it is found in soil and can cause **tinea corporis** or **tinea capitis** in humans, often through contact with contaminated soil. - It is not associated with pityriasis versicolor. *T. tonsurans* - **Trichophyton tonsurans** is an anthropophilic dermatophyte, a common cause of **tinea capitis** (ringworm of the scalp) and sometimes tinea corporis, particularly in children. - It causes specific types of dermatophytosis and is not the causative agent of pityriasis versicolor.

Q: What is the definitive method for diagnosing Pneumocystis jirovecii pneumonia?

Finding cysts in tissue specimens. ***Finding cysts in tissue specimens*** - The definitive diagnosis of **Pneumocystis jirovecii pneumonia (PCP)** involves the microscopic identification of the **trophozoites** or **cysts** of the organism in respiratory secretions or tissue biopsies [1]. - This is typically achieved through techniques like **bronchoalveolar lavage (BAL)**, induced sputum, or transbronchial biopsy, followed by staining with methods such as **Gomori methenamine silver (GMS)** [1] or Giemsa. *Serological test* - Serological tests for PCP are **not definitive** for diagnosis, as antibodies to *P. jirovecii* can be found in a high percentage of healthy individuals due to widespread exposure. - These tests cannot distinguish between active infection, past exposure, or colonization, making them **unreliable** for acute diagnosis. *Chest X-ray* - A chest X-ray can show abnormalities like **diffuse bilateral interstitial infiltrates** or ground-glass opacities, which are highly suggestive of PCP in immunocompromised patients [1]. - However, these findings are **non-specific** and can be present in other pulmonary conditions, thus not providing a definitive diagnosis of PCP. *CT scan of thorax* - A CT scan of the thorax, particularly a **high-resolution CT (HRCT)**, is more sensitive than a chest X-ray and can reveal characteristic patterns such as **ground-glass opacities**, interstitial infiltrates, and sometimes cysts. - While highly suggestive, these imaging findings are **not specific enough** to definitively diagnose PCP and must be correlated with microbiological evidence. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Respiratory Tract Disease, pp. 317-319.

Question 1

Tinea cruris is caused by which of the following fungi?

Accepted Answer

Epidermophyton

Answer

Trichosporon

Answer

Microsporum

Answer

Candida

Question 2

What is the most probable point of entry for Aspergillus?

Accepted Answer

Lungs

Answer

Puncture wound

Answer

Blood

Answer

Gastrointestinal tract

Question 3

P. carinii primarily causes infection in which of the following?

Accepted Answer

Rats

Answer

Mice

Answer

Humans

Answer

Rabbits

Question 4

Which of the following organisms plays an important role in the pathogenesis of "malt worker's lung"?

Accepted Answer

Aspergillus clavatus

Answer

Pseudomonas

Answer

Micropolyspora faeni

Answer

Aspergillus fumigatus

Question 5

Microscopy of a corneal ulcer shows branching septate hyphae. The probable diagnosis is

Accepted Answer

Aspergillus

Answer

Histoplasma

Answer

Candida

Answer

Mucormycosis

Question 6

Which of the following is the MOST COMMON fungal cause of Mucormycosis?

Accepted Answer

Rhizopus oryzae

Answer

Candida albicans

Answer

Aspergillus fumigatus

Answer

Cryptococcus neoformans

Question 7

Which organism is characterized by a wide polysaccharide capsule that appears as a clear halo around the yeast cell on India ink staining?

Accepted Answer

Cryptococcus neoformans

Answer

Penicillium marneffei

Answer

Blastomyces dermatitidis

Answer

Candida albicans

Question 8

A patient, a resident of Himachal Pradesh, presented with a series of ulcers in a row on his right leg. The biopsy from the affected area was taken and cultured on Sabouraud's dextrose agar. What is the most likely causative organism?

Accepted Answer

Sporothrix schenckii

Answer

Cladosporium spp.

Answer

Pseudoallescheria boydii

Answer

Nocardia brasiliensis

Question 9

Pityriasis versicolor is caused by which organism?

Accepted Answer

M. furfur

Answer

E. floccosum

Answer

M. gypseum

Answer

T. tonsurans

Question 10

What is the definitive method for diagnosing Pneumocystis jirovecii pneumonia?

Accepted Answer

Finding cysts in tissue specimens

Answer

Serological test

Answer

Chest X-ray

Answer

CT scan of thorax

Mycology — MCQs

Mycology — MCQs

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