Mycology Practice Questions

Q: Mycotic abscesses are due to:

Fungal infection. ***Correct: Fungal infection*** - The term "mycotic" is derived from the Greek word "mykes," meaning **fungus**. - Therefore, a **mycotic abscess** specifically refers to an abscess caused by a **fungal infection**. - This is a definitional term used in medical microbiology to distinguish fungal abscesses from other etiologies. *Incorrect: Bacterial infection* - Abscesses caused by bacteria are referred to as **bacterial abscesses** or **pyogenic abscesses**, not mycotic abscesses. - While bacteria are the most common cause of abscesses, the term "mycotic" specifically excludes bacterial etiology. *Incorrect: Viral infection* - Viruses typically cause **intracellular infections** and generally do not lead to abscess formation. - Abscesses are characterized by a collection of **pus** and necrotic tissue, which is not a typical pathological feature of viral infections. *Incorrect: Mixed infection* - While a mixed infection could involve multiple pathogens (bacterial + fungal), the term **"mycotic abscess"** specifically indicates a **fungal etiology** as the primary or defining cause. - If bacterial coinfection is present, it may be described separately, but "mycotic" emphasizes the fungal component.

Q: Histoplasma capsulatum, a dimorphic fungus found in soil heavily contaminated with bird droppings, is identified in tissue biopsies by which of the following characteristics?

Oval budding yeasts within macrophages. ***Oval budding yeasts within macrophages*** - In tissue biopsies, **Histoplasma capsulatum** characteristically appears as small, **oval-shaped budding yeasts** that are predominantly found **intracellularly within macrophages**. - This intracellular location is a key diagnostic feature, as the organism can survive and multiply inside these phagocytic cells. *Yeasts with broad-based buds* - This description is characteristic of **Blastomyces dermatitidis**, another dimorphic fungus, which displays large yeasts with a single broad-based bud in tissue. - Unlike *Histoplasma*, **Blastomyces** yeasts are typically much larger and not necessarily intracellular. *Single-cell yeasts with pseudohyphae* - This morphology is characteristic of **Candida albicans**, particularly in its pathogenic forms within tissues. - **Candida** forms true hyphae and pseudohyphae, and its yeasts do not typically reside within macrophages in the same manner as *Histoplasma*. *Arthrospores* - **Arthrospores** (also called arthroconidia) are characteristic of fungi like **Coccidioides immitis**, which appear as barrel-shaped structures in laboratory cultures, but *spherules containing endospores* are seen in tissue. - **Histoplasma** does not form arthrospores in human tissue; it forms yeasts.

Q: Which of the following fungi is known to infect hair?

Trichophyton. ***Trichophyton*** - This genus of fungi is a common cause of **dermatophytosis**, specifically **tinea capitis** and **tinea barbae**, which involve infection of the hair shafts. - **Trichophyton species** have specialized enzymes (keratinases) that allow them to digest keratin, the main protein component of hair. *Epidermophyton* - This genus primarily infects the **skin and nails**, causing conditions like **tinea cruris** (jock itch) and **tinea pedis** (athlete's foot), but typically **does not infect hair**. - Its species, such as *Epidermophyton floccosum*, are generally found in the stratum corneum and do not invade hair follicles. *Malassezia furfur* - *Malassezia furfur* is a yeast that is part of the normal skin flora but can cause superficial infections like **tinea versicolor** and **dandruff** (pityriasis capitis). - While it affects the scalp skin and can be associated with hair follicles, it **does not invade the hair shaft** itself. *None of the options* - This option is incorrect because *Trichophyton* is indeed a well-established fungal genus known for infecting hair.

Q: The reproductive method by which fungi asexually produce rectangular spores by fragmentation of hyphae is known as what?

Arthrospore. ***Arthrospore*** - **Arthrospores** are asexual spores formed by the fragmentation of a pre-existing hypha into rectangular or barrel-shaped cells. - This method of reproduction is characteristic of some fungi, like *Coccidioides immitis*. *Chlamydospore* - **Chlamydospores** are thick-walled, resistant asexual spores formed by the fungal hyphae, typically under unfavorable conditions. - They are typically formed within or at the tip of hyphae, not by fragmentation into rectangular units. *Blastospore* - **Blastospores** are asexual spores produced by budding, characteristic of yeasts and some dimorphic fungi. - This involves the outgrowth of a small bud from a parent cell, which then detaches, rather than hyphal fragmentation. *Conidia* - **Conidia** are asexual spores produced exogenously at the tip of specialized hyphae called conidiophores. - Unlike arthrospores, conidia are not formed by fragmentation of existing hyphae but by asexual budding or mitosis at the conidiophore tip.

Q: Aflatoxins are produced by which organisms?

Aspergillus flavus. ***Aspergillus flavus*** - This fungus is the primary producer of **aflatoxins**, which are potent mycotoxins. - **A. flavus** commonly contaminates crops such as peanuts, corn, and tree nuts under warm, humid conditions. *Aspergillus niger* - While a common species of *Aspergillus*, **A. niger** is not known for producing aflatoxins. - It is often used in industrial applications for the production of citric acid and other enzymes. *Aspergillus fumigatus* - This species is a significant cause of **invasive aspergillosis** in immunocompromised individuals. - It produces other mycotoxins like **gliotoxin** but not aflatoxins. *Candida* - **Candida** is a genus of yeasts, many species of which are normal inhabitants of the human microbiota. - They are known to cause opportunistic infections like **candidiasis**, but they do not produce aflatoxins.

Q: A 40-year-old gardener presents with several subcutaneous nodules on his right hand, where he had cut himself on rose thorns, and physical examination reveals several erythematous fluctuant lesions. Which organism is most likely responsible for his condition?

Sporothrix. ***Sporothrix*** - The gardener's history of a cut from rose thorns and the development of **subcutaneous nodules** are classic presentations of **sporotrichosis** (rose gardener's disease), caused by *Sporothrix schenckii*. - *Sporothrix schenckii* is a **dimorphic fungus** found in soil and on plant matter, causing localized cutaneous or subcutaneous lesions that typically follow **lymphatic spread** (lymphocutaneous pattern). *Aspergillus* - *Aspergillus* species typically cause **invasive pulmonary infections** (aspergillosis) in immunocompromised individuals or allergic bronchopulmonary aspergillosis. - While it can cause cutaneous infections, these are rare and usually occur in severely immunocompromised patients, without the classic "rose thorn" association. *Malassezia* - *Malassezia* species are yeasts that are normal skin flora and are primarily associated with **pityriasis versicolor**, **seborrheic dermatitis**, and **folliculitis**. - They do not typically cause deep subcutaneous nodules or are associated with puncture wounds from plants. *Histoplasma* - *Histoplasma capsulatum* is a **dimorphic fungus** that primarily causes **pulmonary infections** through inhalation of spores from soil contaminated with bird or bat droppings. - While it can rarely cause cutaneous lesions (especially in disseminated disease in immunocompromised patients), it is not associated with traumatic inoculation from plant material or the lymphocutaneous pattern seen here.

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

Question 1

Mycotic abscesses are due to:

Accepted Answer

Fungal infection

Answer

Bacterial infection

Answer

Viral infection

Answer

Mixed infection

Question 2

Histoplasma capsulatum, a dimorphic fungus found in soil heavily contaminated with bird droppings, is identified in tissue biopsies by which of the following characteristics?

Accepted Answer

Oval budding yeasts within macrophages

Answer

Yeasts with broad-based buds

Answer

Single-cell yeasts with pseudohyphae

Answer

Arthrospores

Question 3

Which of the following fungi is known to infect hair?

Accepted Answer

Trichophyton

Answer

Epidermophyton

Answer

Malassezia furfur

Answer

None of the options

Question 4

The reproductive method by which fungi asexually produce rectangular spores by fragmentation of hyphae is known as what?

Accepted Answer

Arthrospore

Answer

Chlamydospore

Answer

Blastospores

Answer

Conidia

Question 5

Aflatoxins are produced by which organisms?

Accepted Answer

Aspergillus flavus

Answer

Aspergillus fumigatus

Answer

Aspergillus niger

Answer

Candida

Question 6

A 40-year-old gardener presents with several subcutaneous nodules on his right hand, where he had cut himself on rose thorns, and physical examination reveals several erythematous fluctuant lesions. Which organism is most likely responsible for his condition?

Accepted Answer

Sporothrix

Answer

Aspergillus

Answer

Malassezia

Answer

Histoplasma

Question 7

Tinea cruris is caused by which of the following fungi?

Accepted Answer

Epidermophyton

Answer

Trichosporon

Answer

Microsporum

Answer

Candida

Question 8

What is the most probable point of entry for Aspergillus?

Accepted Answer

Lungs

Answer

Puncture wound

Answer

Blood

Answer

Gastrointestinal tract

Question 9

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

Accepted Answer

Rats

Answer

Mice

Answer

Humans

Answer

Rabbits

Question 10

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

Mycology — MCQs

Mycology — MCQs

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