Mycology Practice Questions

Q: A deficiency of which of the following cells can predispose to candidiasis?

T Lymphocytes. **Explanation:** The correct answer is **T Lymphocytes**. The body’s defense against *Candida albicans* is a dual mechanism involving both innate and adaptive immunity. 1. **Why T Lymphocytes are correct:** Cell-Mediated Immunity (CMI), specifically **Th17 and Th1 cells**, is crucial for controlling mucocutaneous fungal infections. T lymphocytes produce cytokines (like IL-17 and IL-22) that recruit neutrophils and maintain mucosal integrity. A deficiency in T-cells (as seen in HIV/AIDS or Chronic Mucocutaneous Candidiasis) leads to persistent **mucocutaneous candidiasis** (oral thrush, esophagitis). 2. **Why other options are incorrect:** * **Eosinophils:** These are primarily involved in defense against helminthic (parasitic) infections and type I hypersensitivity reactions; they play a negligible role in fungal defense. * **Macrophages:** While they act as antigen-presenting cells and can ingest yeast, they are not the primary cell type whose *deficiency* characteristically predisposes to candidiasis compared to T-cells or neutrophils. * **Plasma cells:** These produce antibodies (Humoral Immunity). While antibodies can prevent systemic spread, they are not the primary defense against the localized mucosal colonization of *Candida*. **Clinical Pearls for NEET-PG:** * **Dual Defense Rule:** * **T-cell deficiency** predisposes to **Mucocutaneous Candidiasis** (e.g., HIV patients). * **Neutrophil deficiency** (Neutropenia) predisposes to **Disseminated/Systemic Candidiasis** (e.g., chemotherapy patients). * **Th17 cells** are the specific subset of T-cells most vital for fungal immunity at mucosal surfaces. * **Chronic Mucocutaneous Candidiasis (CMC)** is often associated with AIRE gene mutations or STAT1 signaling defects.

Q: An HIV-infected patient presents with oral lesions. What is the most likely causative organism?

Candida. **Explanation:** **Why Candida is the correct answer:** Oropharyngeal Candidiasis (Oral Thrush) is the **most common opportunistic infection** in HIV-infected individuals. It typically occurs when the CD4 count falls below **200-500 cells/mm³**. Clinically, it presents as creamy white, curd-like patches on the tongue or buccal mucosa that can be scraped off, leaving an erythematous base. It is often the first clinical sign of HIV progression. **Analysis of Incorrect Options:** * **A. Epstein-Barr virus (EBV):** While EBV causes **Oral Hairy Leukoplakia** in HIV patients (white, corrugated lesions on the lateral borders of the tongue), it is less common than Candidiasis. Crucially, these lesions *cannot* be scraped off. * **C. Cytomegalovirus (CMV):** CMV typically causes painful, deep **oral ulcers** or esophagitis in severely immunocompromised patients (CD4 < 50 cells/mm³), but it is not the most frequent cause of oral lesions. * **D. Pneumocystis carinii (jirovecii):** This is the most common opportunistic *respiratory* infection (Pneumonia) in HIV patients. While it can rarely present extrapulmonary, it is not a primary cause of oral lesions. **High-Yield Clinical Pearls for NEET-PG:** * **Most common oral manifestation of HIV:** Candidiasis. * **Treatment of choice:** Topical Nystatin or Clotrimazole for mild cases; Oral Fluconazole for moderate to severe cases. * **Oral Hairy Leukoplakia (EBV):** A key diagnostic marker for HIV progression; does not require specific treatment unless symptomatic. * **Kaposi Sarcoma (HHV-8):** Presents as painless, purple/red nodules on the hard palate; it is the most common oral malignancy in HIV.

Q: All of the following are true regarding Cryptococcus neoformans except?

Anticapsular antibody is protective. **Explanation:** *Cryptococcus neoformans* is an encapsulated yeast that primarily causes meningitis. The key to understanding this question lies in the host's immune response to the fungus. **Why Option D is the correct answer (False statement):** In Cryptococcosis, the **cell-mediated immunity (CMI)**—specifically T-cells and macrophages—is the primary defense mechanism. While the body does produce antibodies against the polysaccharide capsule, these **anticapsular antibodies are NOT protective**. They do not aid in clearing the infection, which is why patients with impaired CMI (like those with HIV/AIDS) are highly susceptible regardless of antibody levels. **Analysis of Incorrect Options (True statements):** * **Option A:** It is a classic **opportunistic pathogen**. While it can affect healthy individuals, it most severely affects immunocompromised patients, particularly those with CD4 counts <100 cells/µL. * **Option B:** Like most fungi, *Cryptococcus* grows well on **Sabouraud’s Dextrose Agar (SDA)**, appearing as mucoid, cream-colored colonies. It also grows on Bird Seed Agar (Niger seed agar), producing melanin. * **Option C:** Detection of the **capsular polysaccharide antigen (CrAg)** via Latex Agglutination or Lateral Flow Assay (LFA) in the CSF or serum is a highly sensitive and specific diagnostic gold standard. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Spherical budding yeast with a wide polysaccharide capsule (demonstrated by **India Ink** as a clear halo). * **Virulence Factor:** The capsule is the most important; **Phenoloxidase enzyme** (melanin production) is another. * **Source:** Pigeon droppings and soil. * **Stains:** Mucicarmine (stains capsule red), Fontana-Masson (stains melanin). * **Treatment:** Induction with Amphotericin B + Flucytosine, followed by Fluconazole.

Q: Candidiasis is a complication of all of the following except?

Aspiration pneumonia. **Explanation:** The correct answer is **Aspiration pneumonia**. **1. Why Aspiration Pneumonia is the Correct Answer:** Aspiration pneumonia is typically caused by the inhalation of oropharyngeal or gastric contents into the lower respiratory tract. The primary pathogens involved are **anaerobic bacteria** (e.g., *Bacteroides*, *Fusobacterium*) and aerobic bacteria (e.g., *S. pneumoniae*, *K. pneumoniae*). Candidiasis is not a recognized complication of aspiration pneumonia because the pathophysiology involves chemical irritation and bacterial infection rather than fungal overgrowth. **2. Analysis of Incorrect Options:** * **Prolonged Antibiotic Therapy:** Broad-spectrum antibiotics suppress the normal bacterial flora (e.g., *Lactobacillus*), which usually keeps *Candida* in check. This loss of competition leads to fungal overgrowth, causing oral thrush or vaginal candidiasis. * **Corticosteroid Therapy:** Steroids are immunosuppressive. They inhibit T-cell function and neutrophil activity, reducing the body's ability to fight opportunistic infections like *Candida*. * **Immunocompromised Disease:** Conditions like HIV/AIDS (where CD4 counts drop), diabetes mellitus, and neutropenia are classic risk factors. *Candida* is an opportunistic pathogen that thrives when the host's cellular immunity is impaired. **3. High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** *Candida albicans* is unique because it shows **pseudohyphae** at 37°C and **Germ tubes** (Reynolds-Braude phenomenon) when incubated in serum at 37°C for 2 hours. * **Culture:** Grows on **Sabouraud Dextrose Agar (SDA)** as creamy white, smooth colonies with a "yeasty" odor. * **Chronic Mucocutaneous Candidiasis (CMC):** Associated with T-cell defects and endocrine abnormalities. * **Drug of Choice:** Fluconazole for superficial infections; Echinocandins (e.g., Caspofungin) or Amphotericin B for systemic/invasive candidiasis.

Q: Histoplasma capsulatum is a:

Dimorphic fungus. **Explanation:** *Histoplasma capsulatum* is the causative agent of Histoplasmosis (Darling’s disease). The correct answer is **Dimorphic fungus** because it exhibits two distinct morphological forms depending on the environmental temperature: 1. **At 25°C (Saprophytic phase):** It grows as a mold with hyphae, producing characteristic large, thick-walled, spiked **tuberculate macroconidia**. 2. **At 37°C (Parasitic phase):** It grows as small, oval budding yeast cells within the host’s macrophages. **Analysis of Incorrect Options:** * **A. Protozoa:** Despite its name and its intracellular nature (resembling *Leishmania*), it is a fungus, not a parasite. * **C. Amphotericin resistant:** This is incorrect. Amphotericin B is the gold standard treatment for severe or disseminated Histoplasmosis. * **D. Capsulated:** This is a **classic distractor**. Despite the name *capsulatum*, this fungus is **not** encapsulated. The "halo" seen around the yeast cells in tissue sections is actually a staining artifact caused by the shrinkage of the cytoplasm away from the cell wall. **High-Yield Clinical Pearls for NEET-PG:** * **Habitat:** Found in soil enriched with **bird or bat droppings** (guano); common among cave explorers (Spelunker’s lung). * **Pathogenesis:** It is an **intracellular** pathogen that survives inside **macrophages**. * **Clinical Presentation:** Can mimic Tuberculosis (hilar lymphadenopathy and lung calcifications). * **Diagnosis:** Best diagnosed via fungal culture (SDA) or by observing intracellular yeasts in peripheral blood smears or bone marrow aspirates.

Q: All of the following statements about thrush are true EXCEPT?

It is caused by a gram-negative fungus. **Explanation:** **1. Why Option A is the correct (False) statement:** Thrush is caused by *Candida albicans*, which is a **Gram-positive** yeast. In microbiology, all fungi, including *Candida*, stain Gram-positive because their thick cell walls (containing chitin and glucans) retain the crystal violet dye. Therefore, the statement that it is caused by a "gram-negative fungus" is scientifically incorrect. **2. Analysis of other options:** * **Option B:** Oral thrush (pseudomembranous candidiasis) is characterized by creamy white "curd-like" plaques. These plaques consist of a dense network of fungal hyphae, pseudohyphae, proliferating desquamated epithelial cells, bacteria, and fibrin. * **Option C:** *Candida* is an opportunistic pathogen. Thrush is frequently seen in patients with compromised immunity (HIV/AIDS), those using inhaled corticosteroids, or those with systemic diseases like Diabetes Mellitus. * **Option D:** Neonatal thrush can occur during birth (via the maternal vaginal canal) or spread in nurseries. In institutional settings, it can indeed occur in an epidemic fashion due to cross-contamination via the hands of healthcare workers or contaminated feeding equipment. **High-Yield Clinical Pearls for NEET-PG:** * **The "Scrape" Test:** Unlike leukoplakia, the white plaques of oral thrush **can be scraped off**, leaving behind an erythematous, bleeding base. * **Morphology:** On KOH mount, *Candida* shows budding yeast cells and **pseudohyphae**. * **Drug of Choice:** For mild oral thrush, topical **Clotrimazole** or **Nystatin** suspension is used. For systemic or refractory cases, **Fluconazole** is the preferred agent. * **Risk Factor:** Chronic use of broad-spectrum antibiotics predisposes patients to thrush by altering the normal oral flora.

Q: Which of the following is NOT a characteristic of Cryptococcus neoformans?

A non-encapsulated fungus that infects humans. **Explanation:** The correct answer is **A**. *Cryptococcus neoformans* is defined by its **prominent polysaccharide capsule**, which is its most important virulence factor. This capsule is composed primarily of glucuronoxylomannan (GXM), which inhibits phagocytosis and allows the yeast to evade the host immune system. In clinical practice, this capsule is visualized using **India Ink preparation**, appearing as a clear halo against a dark background. **Analysis of other options:** * **Option B:** It is the most common cause of fungal meningitis, particularly in immunocompromised individuals (HIV/AIDS patients with CD4 counts <100 cells/μL). * **Option C:** *C. neoformans* produces the enzyme **phenoloxidase (laccase)**, which converts phenolic compounds into **melanin**. Melanin protects the fungus from oxidative stress and host immune responses, making it a key virulence factor. This property is used for identification on **Niger Seed (Birdseed) Agar**, where colonies appear brown/black. * **Option D:** Taxonomically, *Cryptococcus* is a **Basidiomycete** yeast. Its sexual state (teleomorph) is known as *Filobasidiella neoformans*. **High-Yield NEET-PG Pearls:** * **Source:** Found in soil enriched with **pigeon droppings**. * **Diagnosis:** **Latex Agglutination Test** (detects capsular antigen) is more sensitive than India Ink. * **Culture:** Grows on Sabouraud Dextrose Agar (SDA) as mucoid, cream-colored colonies. It is **Urease positive**. * **Treatment:** Induction therapy with Amphotericin B + Flucytosine, followed by Fluconazole.

Q: White piedra is caused by which of the following fungi?

Trichosporon beigelii. **Explanation:** **White Piedra** is a superficial fungal infection of the hair shaft characterized by soft, white to light brown nodules. The correct answer is **Trichosporon beigelii** (now often reclassified as *Trichosporon asahii* or other *Trichosporon* species). These nodules are loosely attached to the hair shaft and are composed of hyphae and blastoconidia. It primarily affects the hair of the beard, mustache, and pubic area. **Analysis of Options:** * **A. Piedraia hortae:** This is the causative agent of **Black Piedra**. Unlike white piedra, it produces hard, black, firmly adherent nodules, typically on the scalp hair. * **B. Malassezia globosa:** This lipophilic yeast is the most common cause of **Pityriasis versicolor** (Tinea versicolor), characterized by hypo- or hyperpigmented scaly macules on the trunk. * **C. Hortaea werneckii:** This is the causative agent of **Tinea nigra**, a superficial infection presenting as dark, brownish-black macules on the palms and soles. **NEET-PG High-Yield Pearls:** * **Diagnosis:** Microscopic examination (KOH mount) of white piedra shows transparent hyphae and **arthroconidia**. * **Treatment:** The treatment of choice for both types of Piedra is shaving or cutting the hair. Topical antifungals (azoles) can also be used. * **Differential:** Do not confuse Piedra with **Pediculosis capitis** (nits are oval and on one side of the shaft) or **Trichomycosis axillaris** (caused by *Corynebacterium*, not a fungus). * **Key Distinction:** White Piedra = Soft/Loose/Trichosporon; Black Piedra = Hard/Adherent/Piedraia.

Question 1

A deficiency of which of the following cells can predispose to candidiasis?

Accepted Answer

T Lymphocytes

Answer

Eosinophils

Answer

Macrophages

Answer

Plasma cells

Question 2

A HIV-positive female presents with an indurated ulcer over the tongue. Laboratory findings show growth in cornmeal agar at 20°C, microscopy showing hyphae, and growth in human serum at 37°C showing budding yeasts. What is the probable causative agent?

Accepted Answer

Candida albicans

Answer

Histoplasmosis

Answer

Blastomycosis

Answer

Coccidioidomycosis

Question 3

An HIV-infected patient presents with oral lesions. What is the most likely causative organism?

Accepted Answer

Candida

Answer

Epstein-Barr virus (EBV)

Answer

Cytomegalovirus (CMV)

Answer

Pneumocystis carinii

Question 4

All of the following are true regarding Cryptococcus neoformans except?

Accepted Answer

Anticapsular antibody is protective

Answer

Affects immunocompromised patients

Answer

Grown on Sabouraud's agar

Answer

Capsular antigen can be detected in the CSF

Question 5

Candidiasis is a complication of all of the following except?

Accepted Answer

Aspiration pneumonia

Answer

Prolonged antibiotic therapy

Answer

Corticosteroid therapy

Answer

Immunocompromised disease

Question 6

Histoplasma capsulatum is a:

Accepted Answer

Dimorphic fungus

Answer

Protozoa

Answer

Amphotericin resistant

Answer

Capsulated

Question 7

All of the following statements regarding fungi are true EXCEPT:

Accepted Answer

Dimorphic fungi behave as molds in cultures incubated at 37°C.

Answer

Yeasts are unicellular fungi.

Answer

Candida species can form pseudomycelia.

Answer

Dermatophytes are typically filamentous fungi.

Question 8

All of the following statements about thrush are true EXCEPT?

Accepted Answer

It is caused by a gram-negative fungus

Answer

It is characterized by a plaque of proliferating epithelial and other cells

Answer

It is a complication of immunosuppression or systemic disease

Answer

It can affect neonates in an epidemic fashion

Question 9

Which of the following is NOT a characteristic of Cryptococcus neoformans?

Accepted Answer

A non-encapsulated fungus that infects humans

Answer

Causes meningitis

Answer

Melanin production is related to virulence

Answer

A basidiomycetes yeast

Question 10

White piedra is caused by which of the following fungi?

Accepted Answer

Trichosporon beigelii

Answer

Piedraia hortae

Answer

Malassezia globosa

Answer

Hortaea werneckii

Mycology — MCQs

Mycology — MCQs

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