Mycology Practice Questions

Q: Which is the MOST COMMON cause of atypical pneumonia in the community setting?

Mycoplasma pneumoniae. ***Mycoplasma pneumoniae*** - *Mycoplasma pneumoniae* is the **most common cause of community-acquired atypical pneumonia**, particularly in children and young adults. - It causes "walking pneumonia" with **gradual onset**, low-grade fever, and **prominent dry cough** that is disproportionate to physical findings. - Lacks a **cell wall**, making it resistant to beta-lactam antibiotics; treatment is with macrolides or tetracyclines. - Characterized by **cold agglutinins** and extrapulmonary manifestations (hemolytic anemia, neurologic complications). *Chlamydophila pneumoniae* - A significant cause of atypical pneumonia, but **less common** than *M. pneumoniae* overall. - More common in **older adults** and causes a similar clinical picture with prolonged cough. - Also lacks a cell wall and responds to macrolides or tetracyclines. *Legionella pneumophila* - Causes **Legionnaires' disease**, a severe form of atypical pneumonia. - Less common overall, associated with **contaminated water sources** (cooling towers, hot tubs). - Presents with **high fever, gastrointestinal symptoms**, and hyponatremia; requires specific antibiotics like fluoroquinolones or macrolides. *Chlamydophila psittaci* - Causes **psittacosis** (ornithosis), a rare form of atypical pneumonia. - Acquired through exposure to **infected birds** (parrots, pigeons). - Much **less common** than *M. pneumoniae* in the general community setting.

Q: Which of the following classifications correctly describes fungi?

Eukaryotic organisms. ***Eukaryotic organisms*** - Fungi possess a **true nucleus** enclosed within a nuclear membrane and **membrane-bound organelles** like mitochondria and endoplasmic reticulum. - Their cells have a complex internal structure, distinguishing them from prokaryotes. *Prokaryotic organisms* - **Prokaryotes** lack a true nucleus and membrane-bound organelles; their genetic material is free in the cytoplasm. - Examples of prokaryotes include **bacteria** and archaea, not fungi. *Multicellular organisms* - While many fungi are **multicellular** (e.g., mushrooms), some are **unicellular** (e.g., yeasts), so this classification is not universally descriptive. - Thus, classifying all fungi solely as multicellular would be inaccurate. *Unicellular organisms* - While some fungi, such as **yeasts**, are unicellular, many others, like **molds** and mushrooms, are multicellular. - Therefore, classifying all fungi as unicellular is an **incomplete** description.

Q: The medium of choice for culturing the yeast form of dimorphic fungi is:

Sabouraud's plus antibiotics. ***Sabouraud's plus antibiotics*** - **Sabouraud's dextrose agar** is a common medium for fungi, and the addition of **antibiotics** inhibits bacterial growth, allowing for selective isolation of fungi. - The yeast form of most dimorphic fungi grows best at **35-37°C**, and a rich medium like Sabouraud's with antibiotics provides the necessary nutrients while suppressing contaminants. *Brain-heart infusion* - **Brain-heart infusion (BHI) agar** is a highly nutritious, general-purpose medium that supports the growth of many fastidious organisms, including some fungi and bacteria. - While it can support fungal growth, it is not optimized for selective isolation of dimorphic fungi in their yeast phase and lacks the specific inhibition of bacteria provided by antibiotics. *Sabouraud's* - **Sabouraud's dextrose agar** is a standard fungal culture medium due to its acidic pH and high glucose content, which favor fungal growth over bacterial growth. - However, without antibiotics, it can still be prone to bacterial contamination, making it less ideal for isolating specific fungal forms from mixed samples, especially from clinical specimens. *Any medium incubated at 35-37°C* - While **35-37°C** is the optimal temperature for the yeast phase of dimorphic fungi, simply using "any medium" is insufficient. - The medium must be appropriate for fungal growth (e.g., acidic pH, specific nutrients) and, ideally, should contain agents to **inhibit bacterial overgrowth** for successful isolation and identification from clinical samples.

Q: Which invasive fungal infection is most common in neutropenic patients?

Aspergillus fumigatus. ***Aspergillus fumigatus*** - This species is a frequent cause of invasive aspergillosis, particularly in profoundly **neutropenic** patients or those with **immunocompromise**. - Its spores are ubiquitous in the environment and can cause severe lung infections when inhaled by vulnerable individuals. *Candida* - While *Candida* species are common causes of fungal infections in immunocompromised patients, including those with neutropenia, they typically cause **candidemia** or **mucocutaneous infections**. - **Invasive aspergillosis** is generally considered a more significant opportunistic mold infection in prolonged neutropenia than invasive candidiasis. *Histoplasma* - *Histoplasma capsulatum* is predominantly found in certain **geographic regions** (e.g., Ohio and Mississippi River valleys) and causes **pulmonary or disseminated histoplasmosis**, often after exposure to bird or bat droppings. - It is not as commonly associated with **acute severe neutropenia** as *Aspergillus fumigatus*. *Aspergillus niger* - While *Aspergillus niger* can cause infections, especially **otomycosis** or **aspergilloma**, it is far less commonly implicated in severe **invasive disease** in neutropenic patients compared to *Aspergillus fumigatus*. - *Aspergillus fumigatus* is the most pathogenic and prevalent *Aspergillus* species causing **invasive aspergillosis**.

Q: In an HIV-infected individual, the Gram stain of lung aspirate shows yeast-like morphology. Which of the following is the least likely diagnosis?

Aspergillus fumigatus. ***Aspergillus fumigatus*** - While *Aspergillus* can cause pulmonary infections in immunosuppressed individuals, it typically presents as **hyphae**, not yeast-like morphology, on Gram stain. - Identification usually requires visualization of **septate hyphae with acute-angle branching**. *Candida tropicalis* - *Candida* species are common causes of opportunistic infections in HIV patients and present as **yeast and pseudohyphae** (though true hyphae can also be seen). - *Candida tropicalis* lung infection would appear as **yeast-like forms** on Gram stain, making it a plausible diagnosis. *Cryptococcus neoformans* - *Cryptococcus neoformans* is a significant pathogen in HIV-infected individuals, causing pulmonary and disseminated disease, and is characterized by its **yeast morphology** and prominent capsule. - Staining would reveal **budding yeast cells**, often with a clear halo due to the capsule, fitting the description. *Penicillium marneffei* - *Penicillium marneffei* is a dimorphic fungus endemic in Southeast Asia that causes disseminated infection in HIV patients, and it grows as **yeast-like cells** at body temperature. - In infected tissues, it appears as **intracellular and extracellular oval yeast-like cells** with transverse septation, consistent with the description.

Q: The most common cause of bronchopulmonary aspergillosis is

Aspergillus fumigatus. ***Aspergillus fumigatus*** - This species is the **most common cause** of pulmonary aspergillosis, including allergic bronchopulmonary aspergillosis (ABPA), due to its ubiquitous presence and ability to grow at human body temperature. - It produces **small spores** that can easily reach the lower airways and trigger allergic or invasive responses in susceptible individuals. *Aspergillus clavatus* - This species is less commonly implicated in human disease and is more typically associated with **occupational exposures**, such as in malting barley factories, leading to extrinsic allergic alveolitis. - It is **not a primary cause** of bronchopulmonary aspergillosis in the general population. *Aspergillus niger* - While *A. niger* can cause **otomycosis** and occasionally **aspergilloma**, it is a far less common cause of allergic bronchopulmonary aspergillosis compared to *A. fumigatus*. - It is known for producing black spores, which can sometimes be seen in fungal balls, but its role in pulmonary allergic disease is limited. *Aspergillus flavus* - *A. flavus* is primarily known for producing **aflatoxins** and is more commonly associated with **invasive aspergillosis** in immunocompromised patients, particularly in tropical and subtropical regions. - It is **not the leading cause** of allergic bronchopulmonary aspergillosis.

Q: A 27-year-old intravenous drug user presents with difficulty swallowing. Examination of the oropharynx reveals white plaques along the tongue and the oral mucosa. Which of the following best describes the microscopic appearance of the microorganism responsible for this patient's illness?

Budding yeast and pseudohyphae. ***Budding yeast and pseudohyphae*** - The clinical presentation of **white plaques** in the oropharynx of an **IV drug user** strongly suggests **oral candidiasis** (thrush), caused by *Candida albicans*. - Microscopically, *Candida albicans* is characterized by **budding yeast** forms and the formation of **pseudohyphae** when invading tissues. *Encapsulated yeast* - This description typically refers to *Cryptococcus neoformans*, which is known for its **thick polysaccharide capsule**. - While *Cryptococcus* can cause infections in immunocompromised individuals, it typically presents with **meningitis** or **pulmonary disease**, not oral thrush. *Mold with nonseptate hyphae* - This morphology is characteristic of organisms causing **zygomycosis** (e.g., *Rhizopus*, *Mucor*). - These infections usually present as **rhinocerebral** or **pulmonary involvement** and are not associated with superficial oral plaques like those seen in this patient. *Mold with septate hyphae* - This describes many common molds, including *Aspergillus* species, which typically cause **invasive pulmonary disease**, **sinusitis**, or **allergic bronchopulmonary aspergillosis**. - These organisms are **not typically associated** with oral thrush and produce true hyphae with septations, unlike the pseudohyphae of *Candida*.

Q: The germ tube test is done for:

Candida albicans. ***Candida albicans*** - The **germ tube test** is a rapid screening method used to differentiate *Candida albicans* from other *Candida* species and yeasts. - *Candida albicans* produces **germ tubes** (true hyphae without constrictions at the base) when incubated in serum at 37°C for 2-3 hours. *Chlamydia* - **Chlamydia** species are **obligate intracellular bacteria** and are identified using molecular methods (e.g., NAAT), culture, or immunofluorescence, not the germ tube test. - They do not form structures like germ tubes, as they are prokaryotic organisms. *Bacterial vaginosis* - **Bacterial vaginosis** is a dysbiosis of the vaginal flora, diagnosed based on Amsel criteria (e.g., clue cells, pH >4.5, positive whiff test) or Nugent score from Gram stain. - It involves an overgrowth of various anaerobic bacteria and a decrease in lactobacilli, none of which produce germ tubes. *Neisseria gonorrhoeae* - **Neisseria gonorrhoeae** is a Gram-negative bacterium, typically identified by Gram stain showing intracellular **Gram-negative diplococci** within neutrophils, and subsequent culture or NAAT. - As a bacterium, it does not form germ tubes; this test is specific to certain fungi.

Question 1

Which is the MOST COMMON cause of atypical pneumonia in the community setting?

Accepted Answer

Mycoplasma pneumoniae

Answer

Legionella pneumophila

Answer

Chlamydophila psittaci

Answer

Chlamydophila pneumoniae

Question 2

Which of the following classifications correctly describes fungi?

Accepted Answer

Eukaryotic organisms

Answer

Prokaryotic organisms

Answer

Multicellular organisms

Answer

Unicellular organisms

Question 3

The medium of choice for culturing the yeast form of dimorphic fungi is:

Accepted Answer

Sabouraud's plus antibiotics

Answer

Any medium incubated at 35-37°C

Answer

Brain-heart infusion

Answer

Sabouraud's

Question 4

Which invasive fungal infection is most common in neutropenic patients?

Accepted Answer

Aspergillus fumigatus

Answer

Histoplasma

Answer

Aspergillus niger

Answer

Candida

Question 5

In an HIV-infected individual, the Gram stain of lung aspirate shows yeast-like morphology. Which of the following is the least likely diagnosis?

Accepted Answer

Aspergillus fumigatus

Answer

Candida tropicalis

Answer

Cryptococcus neoformans

Answer

Penicillium marneffei

Question 6

The most common cause of bronchopulmonary aspergillosis is

Accepted Answer

Aspergillus fumigatus

Answer

Aspergillus niger

Answer

Aspergillus clavatus

Answer

Aspergillus flavus

Question 7

A 27-year-old intravenous drug user presents with difficulty swallowing. Examination of the oropharynx reveals white plaques along the tongue and the oral mucosa. Which of the following best describes the microscopic appearance of the microorganism responsible for this patient's illness?

Accepted Answer

Budding yeast and pseudohyphae

Answer

Encapsulated yeast

Answer

Mold with nonseptate hyphae

Answer

Mold with septate hyphae

Question 8

The germ tube test is done for:

Accepted Answer

Candida albicans

Answer

Neisseria gonorrhoeae

Answer

Bacterial vaginosis

Answer

Chlamydia

Mycology — MCQs

Mycology — MCQs

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