Mycology Practice Questions

Q: In an immunocompromised patient with pulmonary symptoms, bronchoalveolar lavage reveals septate hyphae with acute angle branching. What is the likely pathogen?

Aspergillus fumigatus. ***Aspergillus fumigatus*** - The presence of **septate hyphae with acute angle branching** (approximately 45 degrees) is the classic microscopic hallmark for **Aspergillus** species. - In immunocompromised patients, this pathogen often causes **Invasive Pulmonary Aspergillosis**, manifesting with cough, hemoptysis, and characteristic **halo signs** on CT imaging. *Mucor species* - Characterized by **non-septate** (or sparsely septate) hyphae that are **broad** and ribbon-like with **right-angle (90 degree) branching**. - Commonly associated with **diabetic ketoacidosis** or neutropenia, often causing aggressive **rhinocerebral** or pulmonary infections. *Histoplasma capsulatum* - Microscopic examination typically reveals small **intracellular oval yeasts** within **macrophages**, rather than large branching hyphae. - This **dimorphic fungus** is typically associated with exposure to **bird or bat droppings** in endemic areas like the Ohio and Mississippi River valleys. *Candida albicans* - Seen as **budding yeasts** and **pseudohyphae** (terminating in blastoconidia) rather than true septate hyphae with acute branching. - While it can cause systemic infection, primary **Candida pneumonia** is rare and usually represents disseminated **candidemia** or oral contamination in BAL samples.

Q: A 55-year-old farmer from the Midwest presents with a chronic cough and weight loss. A chest X-ray shows calcified granulomas, and a sputum culture reveals a dimorphic fungus. What is the most likely diagnosis?

Histoplasmosis. ***Histoplasmosis*** - This fungus is endemic to the **Midwest** (Ohio and Mississippi river valleys) and is often associated with exposure to **bird or bat droppings**. - **Calcified granulomas** on chest X-ray and a **dimorphic fungus** on sputum culture are classic findings in chronic histoplasmosis. Chronic marks of the disease are typically managed with long-term antifungal therapy [1]. *Coccidioidomycosis* - This fungus is primarily found in the **Southwestern United States** and parts of Mexico and Central/South America ("desert rheumatism"). - While it can cause pulmonary symptoms and granulomas, its endemic region does not match the patient's geographic location. *Blastomycosis* - Blastomycosis is also endemic to the **Midwest** but commonly presents with skin lesions, bone involvement, and lung disease with broader-based budding yeast. - While it can cause pulmonary issues, the presence of **calcified granulomas** points more specifically towards histoplasmosis. *Paracoccidioidomycosis* - This fungal infection is largely restricted to **Central and South America**, making it highly unlikely for a patient from the Midwest to acquire it without travel history. - It typically presents with chronic progressive pulmonary disease and mucocutaneous lesions, with characteristic "pilot wheel" yeast forms.

Q: A laboratory technician develops a pruritic rash and fever after handling soil samples. A skin biopsy reveals septate hyphae. What is the likely organism involved?

Trichophyton rubrum. ***Correct: Trichophyton rubrum*** - **_Trichophyton rubrum_** is the **most common dermatophyte** causing cutaneous mycoses worldwide - Demonstrates **septate hyphae** on histopathology with KOH preparation or biopsy - Primarily **anthropophilic** (human-to-human transmission), causing chronic tinea infections (tinea pedis, cruris, corporis, unguium) - Among the options given, it is the most likely dermatophyte to present with septate hyphae on skin biopsy *Incorrect: Candida albicans* - Typically appears as **budding yeast with pseudohyphae**, not true septate hyphae - Causes mucocutaneous candidiasis (thrush, intertrigo, vulvovaginitis) - Not typically associated with soil exposure or significant systemic symptoms in immunocompetent hosts *Incorrect: Aspergillus niger* - Forms **septate hyphae with acute angle branching** but primarily causes **respiratory infections** (aspergilloma, invasive pulmonary aspergillosis) - **Primary cutaneous aspergillosis** is rare, typically occurring at sites of trauma in immunocompromised patients - Would not be the first consideration for a pruritic rash in an immunocompetent individual *Incorrect: Microsporum canis* - A **zoophilic dermatophyte** acquired primarily from cats and dogs - Causes tinea capitis (especially in children) and tinea corporis - Also shows septate hyphae, but **soil exposure is not the typical epidemiological link** - animal contact is key - Less common than _T. rubrum_ in adults for cutaneous infections **Clinical Note:** While the soil exposure history might initially suggest a geophilic organism like _Microsporum gypseum_ or _Sporothrix schenckii_ (not listed), among the given options, _T. rubrum_ remains the most common dermatophyte encountered in clinical practice that presents with septate hyphae on biopsy.

Q: A patient with diabetes presents with a black eschar on the nose and facial swelling. A biopsy shows broad, non-septate hyphal elements with right-angle branching. Assess the likely diagnosis and the urgency of the management required.

Mucormycosis, immediate aggressive treatment. ***Mucormycosis, immediate aggressive treatment*** - The presence of a **black eschar**, **facial swelling** in a diabetic patient, and biopsy findings of **broad, non-septate hyphal elements with right-angle branching** are classic for **mucormycosis** [1]. - This is an **opportunistic fungal infection** that is rapidly progressive and highly fatal, requiring **immediate aggressive treatment** including surgical debridement and antifungal therapy (e.g., amphotericin B) [1]. *Aspergillosis, elective treatment* - **Aspergillosis** typically presents with **septate hyphae with acute angle branching**, which differs from the *non-septate, right-angle branching* seen in the biopsy. - While serious, it does not typically manifest with a **black eschar** as the primary sign of rhino-orbital-cerebral involvement; also, the urgency described for mucormycosis is much higher than for most forms of aspergillosis. *Candidiasis, standard antifungal treatment* - **Candidiasis** usually presents with **pseudohyphae and budding yeasts**; it does not exhibit the *broad, non-septate hyphal elements* described. - While fungal, it rarely causes a **necrotic black eschar** in the absence of severe systemic involvement in immunocompromised patients, and its treatment regimen is generally less urgent and aggressive than for mucormycosis. *Dermatophytosis, topical treatment* - **Dermatophytosis (ringworm)** is a **superficial fungal infection** of the skin, hair, or nails, typically presenting with *erythematous, scaly lesions*. - It would not cause a **black eschar** or facial swelling indicative of deep tissue invasion, nor would the biopsy show *broad, non-septate hyphae* in the manner described.

Q: In a patient with AIDS and a CD4 count of fewer than 50 cells/µL, which of the following opportunistic infections is most likely to occur?

Cryptococcus neoformans. ***Cryptococcus neoformans*** - **Cryptococcal meningitis** is a common and severe opportunistic infection in AIDS patients with **CD4 counts below 50 cells/µL** [1]. - It often presents with **headache**, **fever**, **nuchal rigidity**, and altered mental status. *Candida albicans* - While common in AIDS patients, **oral candidiasis (thrush)** typically occurs at **higher CD4 counts** (e.g., below 200 cells/µL) and is less indicative of a CD4 count below 50 cells/µL compared to cryptococcosis [2]. - Systemic candidiasis is less common than oral or esophageal forms in this setting [1]. *Aspergillus fumigatus* - **Aspergillosis** is typically seen in patients with **severe neutropenia** and profound immunosuppression, often related to hematological malignancies or transplant, rather than solely based on low CD4 count in AIDS. - It is less likely to be the *most likely* opportunistic infection at a CD4 count of fewer than 50 cells/µL in an HIV patient presenting with typical symptoms of opportunistic infection. *Histoplasma capsulatum* - **Disseminated histoplasmosis** can occur in AIDS patients with CD4 counts below 100-150 cells/µL, but it is **geographically localized** to endemic areas (e.g., Ohio and Mississippi River valleys) [3]. - Cryptococcal meningitis is more universally prevalent in AIDS patients with very low CD4 counts, making it a more likely general answer.

Q: A 45-year-old patient with a history of poorly controlled diabetes presents with sinus pain, nasal discharge, and facial swelling. A biopsy reveals broad, nonseptate hyphae branching at wide angles. What is the most likely causative agent?

Rhizopus spp.. ***Rhizopus spp.*** - The patient's presentation with **sinus pain**, **nasal discharge**, **facial swelling**, and a history of **poorly controlled diabetes** is classic for **mucormycosis** (also known as zygomycosis). - **Biopsy findings** of **broad, nonseptate hyphae branching at wide/irregular angles** are pathognomonic for mucormycosis, most commonly caused by *Rhizopus* species. - Diabetes mellitus, particularly when poorly controlled with **ketoacidosis**, is a major risk factor for rhinocerebral mucormycosis. *Aspergillus fumigatus* - This fungus typically causes infections with **septate hyphae** that **branch at acute angles** (45 degrees), which is morphologically distinct from mucormycosis. - While *Aspergillus* can cause invasive sinusitis in immunocompromised patients, the specific hyphal morphology (nonseptate, wide-angle branching) points away from it. *Candida albicans* - *Candida albicans* is a yeast that typically appears as **oval budding cells** and **pseudohyphae** on microscopy, not broad, nonseptate hyphae. - While it can cause opportunistic infections in diabetic and immunocompromised patients, its microscopic appearance is entirely inconsistent with the biopsy findings. *Cryptococcus neoformans* - *Cryptococcus neoformans* is an **encapsulated yeast** that is typically identified by its **spherical or oval budding cells** with a characteristic **polysaccharide capsule** visible with India ink stain. - It primarily causes **meningitis** and pulmonary infections in immunocompromised hosts, and its morphology (yeast, not hyphae) is entirely different from the described findings.

Q: A 50-year-old farmer with diabetes presents with a chronic ulcer on his foot that has not healed despite standard wound care. A biopsy reveals fungal elements, and the culture grows a mold with septate hyphae and green conidia. What is the likely causative organism?

Aspergillus fumigatus. **Aspergillus fumigatus** - The presence of **septate hyphae** and **green conidia** on culture is characteristic of *Aspergillus* species, particularly *Aspergillus fumigatus*. - Patients with **diabetes** are at a higher risk for fungal infections, and chronic non-healing ulcers can be a presentation of localized **aspergillosis**. *Candida albicans* - *Candida albicans* typically presents as **yeast** and **pseudohyphae** on microscopy, not septate hyphae with green conidia. - While it can cause chronic ulcers, its microscopic morphology and culture characteristics differ significantly from the description. *Rhizopus oryzae* - *Rhizopus oryzae* is a **mucormycete** characterized by **broad, aseptate hyphae** with right-angle branching, which contrasts with the septate hyphae described. - It causes mucormycosis, a severe infection often involving the rhinocerebral area, though cutaneous forms can occur. *Histoplasma capsulatum* - *Histoplasma capsulatum* is a **dimorphic fungus** that appears as small, oval budding yeasts within macrophages in tissue. - It is typically associated with pulmonary infections and disseminated disease, not chronic foot ulcers with septate hyphae and green conidia on culture.

Q: A patient with AIDS presents with meningitis. An India ink preparation of the cerebrospinal fluid shows encapsulated yeast cells. Which organism is most likely responsible?

Cryptococcus neoformans. ***Cryptococcus neoformans*** - This organism is a **common cause of meningitis in AIDS patients** due to their severely compromised immune systems (low CD4 counts). - The presence of **encapsulated yeast cells** visible on an **India ink preparation of CSF** is pathognomonic for *Cryptococcus neoformans*. - The **India ink negative staining technique** highlights the thick polysaccharide capsule, which appears as a clear halo around the yeast cells against a dark background. *Candida albicans* - While *Candida albicans* can cause various infections in immunocompromised individuals, **Candidal meningitis is rare** and would not typically show encapsulated yeast on India ink. - *Candida* usually presents as **pseudohyphae and budding yeasts** and is not primarily identified by India ink preparations for capsules in CSF. *Histoplasma capsulatum* - *Histoplasma capsulatum* can cause **disseminated histoplasmosis**, including central nervous system involvement, especially in AIDS patients. - However, it is an **intracellular dimorphic fungus** and does not typically present as encapsulated yeast in the CSF on India ink stain. *Coccidioides immitis* - *Coccidioides immitis* can cause **Coccidioidal meningitis**, particularly in endemic areas and immunocompromised patients. - It is characterized by **spherules containing endospores** in tissue and CSF, not encapsulated yeast cells.

Q: A patient presents with a chronic non-healing ulcer on the foot. Culture reveals the growth of a dimorphic fungus. Which of the following is the most likely diagnosis?

Sporotrichosis. ***Sporotrichosis*** - **Sporotrichosis** is characterized by subcutaneous nodules and **non-healing ulcers**, often following **thorn pricks** or other trauma, particularly in gardeners. - The fungus **_Sporothrix schenckii_** is dimorphic, growing as a mold in the environment and as a yeast in human tissue at body temperature. *Candidiasis* - **Candidiasis** typically presents as **mucocutaneous infections** (e.g., thrush, vaginitis, diaper rash) or systemic infections in immunocompromised individuals [1]. - While _Candida_ is a yeast, it is not dimorphic in the same way as the fungi causing deep mycoses, and chronic non-healing ulcers on the foot are not its typical presentation unless associated with severe immunosuppression [1]. *Histoplasmosis* - **Histoplasmosis** primarily affects the **lungs** following inhalation of spores from bird or bat droppings, leading to pneumonia-like symptoms or disseminated disease in immunocompromised patients. - While _Histoplasma capsulatum_ is a dimorphic fungus, localized cutaneous ulcers are rare and usually occur as part of disseminated disease, not as an isolated foot ulcer. *Blastomycosis* - **Blastomycosis** can cause **cutaneous lesions**, including ulcers and verrucous (wart-like) lesions, in addition to pulmonary and disseminated disease. - However, it is less commonly associated with the specific "non-healing ulcer on the foot" scenario compared to sporotrichosis, which often involves local inoculation and lymphatic spread.

Q: A patient presents with worsening respiratory distress following a bone marrow transplant. A chest CT reveals diffuse, bilateral, ground-glass opacities. Gomori methenamine silver stain of bronchoalveolar lavage fluid shows cup-shaped yeast forms. What is the probable diagnosis?

Pneumocystis jirovecii pneumonia. ***Pneumocystis jirovecii pneumonia*** - The combination of **worsening respiratory distress** in an immunocompromised patient (post-bone marrow transplant), **diffuse bilateral ground-glass opacities** on CT, and **cup-shaped yeast forms** on Gomori methenamine silver (GMS) stain of BAL fluid is pathognomonic for **Pneumocystis jirovecii pneumonia (PJP)** [1]. - PJP is an **opportunistic fungal infection** common in severely immunocompromised individuals, characteristically presenting with these radiological and microscopic findings [1]. *Cryptococcus neoformans infection* - **Cryptococcus neoformans** typically presents with **meningitis** or pulmonary nodules/masses, not diffuse ground-glass opacities. - While it can manifest in immunocompromised patients, microscopic examination reveals **encapsulated yeast cells** that stain with India ink, not cup-shaped forms with GMS. *Candida albicans pneumonia* - **Candida albicans** can cause pneumonia in severely immunocompromised patients, but it usually presents as **bronchopneumonia** or **abscesses**, not diffuse ground-glass opacities. - Microscopically, Candida appears as **budding yeast with pseudohyphae**, which are distinct from the cup-shaped forms seen in PJP. *Aspergillus fumigatus infection* - **Aspergillus fumigatus** in immunocompromised patients commonly causes **invasive aspergillosis**, presenting clinically with **fever**, **cough**, and **hemoptysis**. - Radiologically, it often presents with **nodules**, **cavitation**, or the **halo sign**, distinguishing it from the diffuse ground-glass opacities seen in PJP. Microscopy would show **septate hyphae with acute angle branching**.

Question 1

In an immunocompromised patient with pulmonary symptoms, bronchoalveolar lavage reveals septate hyphae with acute angle branching. What is the likely pathogen?

Accepted Answer

Aspergillus fumigatus

Answer

Mucor species

Answer

Histoplasma capsulatum

Answer

Candida albicans

Question 2

A 55-year-old farmer from the Midwest presents with a chronic cough and weight loss. A chest X-ray shows calcified granulomas, and a sputum culture reveals a dimorphic fungus. What is the most likely diagnosis?

Accepted Answer

Histoplasmosis

Answer

Coccidioidomycosis

Answer

Blastomycosis

Answer

Paracoccidioidomycosis

Question 3

A laboratory technician develops a pruritic rash and fever after handling soil samples. A skin biopsy reveals septate hyphae. What is the likely organism involved?

Accepted Answer

Trichophyton rubrum

Answer

Candida albicans

Answer

Aspergillus niger

Answer

Microsporum canis

Question 4

A patient with diabetes presents with a black eschar on the nose and facial swelling. A biopsy shows broad, non-septate hyphal elements with right-angle branching. Assess the likely diagnosis and the urgency of the management required.

Accepted Answer

Mucormycosis, immediate aggressive treatment

Answer

Aspergillosis, elective treatment

Answer

Candidiasis, standard antifungal treatment

Answer

Dermatophytosis, topical treatment

Question 5

In a patient with AIDS and a CD4 count of fewer than 50 cells/µL, which of the following opportunistic infections is most likely to occur?

Accepted Answer

Cryptococcus neoformans

Answer

Candida albicans

Answer

Aspergillus fumigatus

Answer

Histoplasma capsulatum

Question 6

A 45-year-old patient with a history of poorly controlled diabetes presents with sinus pain, nasal discharge, and facial swelling. A biopsy reveals broad, nonseptate hyphae branching at wide angles. What is the most likely causative agent?

Accepted Answer

Rhizopus spp.

Answer

Aspergillus fumigatus

Answer

Candida albicans

Answer

Cryptococcus neoformans

Question 7

A 50-year-old farmer with diabetes presents with a chronic ulcer on his foot that has not healed despite standard wound care. A biopsy reveals fungal elements, and the culture grows a mold with septate hyphae and green conidia. What is the likely causative organism?

Accepted Answer

Aspergillus fumigatus

Answer

Candida albicans

Answer

Rhizopus oryzae

Answer

Histoplasma capsulatum

Question 8

A patient with AIDS presents with meningitis. An India ink preparation of the cerebrospinal fluid shows encapsulated yeast cells. Which organism is most likely responsible?

Accepted Answer

Cryptococcus neoformans

Answer

Candida albicans

Answer

Histoplasma capsulatum

Answer

Coccidioides immitis

Question 9

A patient presents with a chronic non-healing ulcer on the foot. Culture reveals the growth of a dimorphic fungus. Which of the following is the most likely diagnosis?

Accepted Answer

Sporotrichosis

Answer

Candidiasis

Answer

Histoplasmosis

Answer

Blastomycosis

Question 10

A patient presents with worsening respiratory distress following a bone marrow transplant. A chest CT reveals diffuse, bilateral, ground-glass opacities. Gomori methenamine silver stain of bronchoalveolar lavage fluid shows cup-shaped yeast forms. What is the probable diagnosis?

Accepted Answer

Pneumocystis jirovecii pneumonia

Answer

Cryptococcus neoformans infection

Answer

Candida albicans pneumonia

Answer

Aspergillus fumigatus infection

Mycology — MCQs

Mycology — MCQs

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