Mycology — MCQs
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Dermatophytosis is caused by which of the following?
A 20-year-old uncontrolled diabetic presents with sinus swelling and a black necrotic mass in the nasal cavity. Which organism is most likely responsible?
The 1,3-\\u03b2-D-glucan test can be used for the diagnosis of all of the following infections except?
Which of the following statements about Cryptococcus is FALSE?
A recent immigrant from rural Brazil presents with a swollen face and extremely poor dental hygiene, including loss of an adult tooth, which appears to be the focus of the current infection. There are two open ulcers on the outside of the swollen cheek. Small yellow "grains" are seen in one of the ulcers. Gram stain shows purple-staining fine filaments. What is the most likely disease?
Aflatoxin is produced by which fungus?
How is Pneumocystis jirovecii diagnosed?
How many episodes of vulval candidiasis per year are needed for the diagnosis of recurrent vulvovaginal candidiasis?
A patient with severe mycotic infection, diabetes mellitus, and cellulitis is suffering from which condition?
Which of the following is the rarest opportunistic fungal infection seen in an AIDS patient?
Mycology Indian Medical PG Practice Questions and MCQs
Question 161: Dermatophytosis is caused by which of the following?
- A. Herpes simplex
- B. Papilloma virus
- C. Trichophyton (Correct Answer)
- D. Candida
Explanation: **Explanation:** **Dermatophytosis** (commonly known as Tinea or Ringworm) is a superficial fungal infection of keratinized tissues such as the skin, hair, and nails. It is caused by a group of fungi called **Dermatophytes**, which possess the enzyme **keratinase** to digest keratin. 1. **Why Trichophyton is correct:** Dermatophytes are classified into three genera based on their morphological characteristics: * **Trichophyton:** Affects skin, hair, and nails. (Most common genus). * **Microsporum:** Affects skin and hair (rarely nails). * **Epidermophyton:** Affects skin and nails (never hair). * *Trichophyton rubrum* is the most common cause of dermatophytosis worldwide. 2. **Why other options are incorrect:** * **Herpes simplex (A) & Papilloma virus (B):** These are viral pathogens. Herpes causes vesicular eruptions (cold sores/genital herpes), while HPV causes warts and is linked to cervical cancer. * **Candida (D):** While *Candida* is a fungus, it causes **Candidiasis** (e.g., oral thrush, vaginitis). Unlike dermatophytes, it is a yeast-like fungus that is part of the normal flora and typically causes opportunistic infections involving mucous membranes. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnosis:** The gold standard screening is **KOH mount**, which shows branching septate hyphae. * **Culture:** Sabouraud’s Dextrose Agar (SDA) is used; *Trichophyton* species often show characteristic microconidia and macroconidia. * **Wood’s Lamp:** Useful for *Microsporum* (shows bright green fluorescence), but most *Trichophyton* species (except *T. schoenleinii*) do not fluoresce. * **Treatment:** Topical azoles or Terbinafine are first-line; Griseofulvin is used for Tinea capitis.
Question 162: A 20-year-old uncontrolled diabetic presents with sinus swelling and a black necrotic mass in the nasal cavity. Which organism is most likely responsible?
- A. Mucormycosis (Correct Answer)
- B. Actinomycosis
- C. Rhinosporidiosis
- D. Cryptococcus
Explanation: ### Explanation **Correct Answer: A. Mucormycosis** The clinical presentation of a **diabetic patient** with **sinus swelling** and a **black necrotic mass** (eschar) is a classic description of **Rhinocerebral Mucormycosis**. * **Pathophysiology:** Mucormycosis (caused by *Rhizopus*, *Mucor*, or *Lichtheimia*) is an opportunistic fungal infection. In diabetic ketoacidosis (DKA), the fungi utilize ketone reductase to thrive in acidic, glucose-rich environments. * **The "Black Eschar":** These fungi are **angioinvasive**, meaning they invade blood vessel walls, leading to thrombosis and subsequent tissue infarction. This necrosis manifests clinically as the characteristic black eschar in the nasal cavity or palate. --- ### Why the other options are incorrect: * **B. Actinomycosis:** Caused by *Actinomyces israelii* (a filamentous bacterium, not a fungus). It typically presents as "lumpy jaw" with chronic abscesses and **sulfur granules** in the pus, not acute necrotic masses in diabetics. * **C. Rhinosporidiosis:** Caused by *Rhinosporidium seeberi*. It presents as friable, **strawberry-like leafy polyps** in the nose, usually in patients with a history of bathing in stagnant water. It is not associated with diabetes or necrosis. * **D. Cryptococcus:** Primarily causes meningitis or pulmonary infections in immunocompromised patients. It does not typically cause angioinvasive sinus necrosis. --- ### High-Yield Clinical Pearls for NEET-PG: 1. **Microscopy:** Look for **broad, aseptate hyphae** with **branching at right angles (90°)**. (Contrast with *Aspergillus*, which has narrow, septate hyphae branching at 45°). 2. **Risk Factors:** Uncontrolled Diabetes (DKA), neutropenia, and iron overload (use of deferoxamine). 3. **Treatment:** Immediate surgical debridement and intravenous **Liposomal Amphotericin B**. 4. **Culture:** Grows on Sabouraud Dextrose Agar (SDA) as "cotton candy" colonies.
Question 163: The 1,3-\\u03b2-D-glucan test can be used for the diagnosis of all of the following infections except?
- A. Invasive Aspergillosis
- B. Invasive Candidiasis and Candidemia
- C. Pneumocystis Jiroveci pneumonia
- D. Cryptococcal meningitis (Correct Answer)
Explanation: **Explanation:** The **1,3-β-D-glucan (BDG) test** (often referred to as the Fungitell assay) is a pan-fungal biomarker used for the presumptive diagnosis of invasive fungal diseases. It detects 1,3-β-D-glucan, a major polysaccharide component found in the **cell walls** of most pathogenic fungi. **Why Cryptococcus is the Correct Answer:** While *Cryptococcus neoformans* does possess 1,3-β-D-glucan in its cell wall, it is produced in **very low amounts**. More importantly, the fungus possesses a **thick polysaccharide capsule** that surrounds the cell wall, preventing the release of BDG into the bloodstream. Therefore, the BDG test is characteristically **negative** in Cryptococcal infections. The gold standard for diagnosis remains the Cryptococcal Antigen (CrAg) test (Lateral Flow Assay or Latex Agglutination). **Analysis of Other Options:** * **Invasive Aspergillosis:** *Aspergillus* species have high concentrations of BDG in their cell walls; thus, the test is highly sensitive (alongside the Galactomannan assay). * **Invasive Candidiasis:** *Candida* species are the most common cause of a positive BDG test. It is a vital tool for early diagnosis of candidemia. * **Pneumocystis jirovecii:** Despite being an atypical fungus, *P. jirovecii* produces abundant BDG during its trophic and cyst stages. It is a highly sensitive (though not specific) serum marker for PJP. **High-Yield Clinical Pearls for NEET-PG:** * **"Exceptional" Fungi:** The BDG test is typically **negative** in **Cryptococcosis**, **Zygomycosis (Mucormycosis)**, and **Blastomycosis**. * **False Positives:** Can occur due to hemodialysis (cellulose membranes), treatment with certain antibiotics (Amoxicillin-Clavulanate, Piperacillin-Tazobactam), or exposure to surgical gauze/sponges. * **Zygomycetes (Mucor/Rhizopus):** These lack 1,3-β-D-glucan entirely (they have more chitin and chitosan), making BDG a useful tool to differentiate Aspergillosis from Mucormycosis.
Question 164: Which of the following statements about Cryptococcus is FALSE?
- A. Primarily infects the lung
- B. Is urease negative (Correct Answer)
- C. Diagnosis can be aided by India ink staining
- D. All the other statements are true
Explanation: **Explanation:** *Cryptococcus neoformans* is an encapsulated yeast that is a significant pathogen, particularly in immunocompromised patients (e.g., those with HIV/AIDS). **1. Why Option B is the Correct (False) Statement:** The statement "Is urease negative" is incorrect because **Cryptococcus is characteristically urease positive.** This is a key biochemical marker used in the laboratory to differentiate it from other yeasts like *Candida albicans* (which is urease negative). The production of the urease enzyme allows the organism to hydrolyze urea into ammonia, which can be detected by a color change in Christensen’s urea agar. **2. Analysis of Other Options:** * **Option A (Primarily infects the lung):** This is true. The primary route of infection is the inhalation of basidiospores from the environment (often associated with pigeon droppings). While it is famous for causing meningitis, the **lung is the primary portal of entry** and the initial site of infection. * **Option C (Diagnosis aided by India ink):** This is true. The large polysaccharide capsule of *Cryptococcus* does not take up the ink, creating a characteristic **"halo" appearance** against a dark background. This is a classic, rapid bedside test for CSF samples. **High-Yield Clinical Pearls for NEET-PG:** * **Virulence Factor:** The **Polysaccharide Capsule** (GXM) is the most important virulence factor; it is antiphagocytic. * **Culture:** Grows on **Sabouraud Dextrose Agar (SDA)** as mucoid, cream-colored colonies. * **Phenoloxidase Enzyme:** *Cryptococcus* produces melanin when grown on **Niger Seed Agar (Bird Seed Agar)**, appearing as brown/black colonies. * **Antigen Detection:** The **CrAg (Cryptococcal Antigen)** test via Latex Agglutination or LFA is more sensitive and specific than India ink. * **Treatment:** Induction therapy usually involves **Amphotericin B + Flucytosine**, followed by Fluconazole.
Question 165: A recent immigrant from rural Brazil presents with a swollen face and extremely poor dental hygiene, including loss of an adult tooth, which appears to be the focus of the current infection. There are two open ulcers on the outside of the swollen cheek. Small yellow "grains" are seen in one of the ulcers. Gram stain shows purple-staining fine filaments. What is the most likely disease?
- A. Actinomycotic mycetoma (Correct Answer)
- B. Chromomycosis
- C. Eumycotic mycetoma
- D. Sporotrichosis
Explanation: **Explanation:** The clinical presentation points toward **Actinomycotic mycetoma** (specifically cervicofacial actinomycosis). The key diagnostic clues are the location (swollen face/cheek), association with poor dental hygiene or dental trauma (tooth loss), and the presence of **"sulfur granules"** (small yellow grains) discharging from sinus tracts. 1. **Why it is correct:** Actinomycetes are Gram-positive, anaerobic, or microaerophilic bacteria that form **fine, branching filaments** (resembling fungi, hence the name). On Gram stain, these appear as **purple-staining fine filaments**. The "sulfur granules" are actually microcolonies of the bacteria surrounded by inflammatory cells. 2. **Why other options are wrong:** * **Eumycotic mycetoma:** Caused by true fungi (e.g., *Madurella*). While it also presents with grains and swelling, the filaments would be much thicker (>2–4 μm), septate, and would not stain typically Gram-positive; they are better visualized with KOH or silver stains. * **Chromomycosis:** Characterized by "cauliflower-like" skin lesions and the presence of **Medlar bodies** (copper-penny bodies) on histology, not fine filaments or sulfur granules. * **Sporotrichosis:** Typically follows a "lymphocutaneous" spread (nodules along lymphatics) after a rose-gardener’s injury. It is a dimorphic fungus appearing as cigar-shaped yeast cells, not filaments in tissue. **High-Yield NEET-PG Pearls:** * **Actinomyces israelii** is the most common causative agent. * It is **not** acid-fast (unlike *Nocardia*, which is weakly acid-fast). * **Molar tooth appearance:** The characteristic colony morphology on anaerobic culture (Agar). * **Treatment:** High-dose Penicillin G is the drug of choice (DOC). Surgery may be required for abscess drainage.
Question 166: Aflatoxin is produced by which fungus?
- A. Aspergillus flavus (Correct Answer)
- B. Aspergillus fumigatus
- C. Claviceps purpurea
- D. Argemone mexicana
Explanation: **Explanation:** **Aflatoxins** are potent mycotoxins primarily produced by **Aspergillus flavus** and *Aspergillus parasiticus*. These fungi commonly contaminate stored agricultural crops such as groundnuts (peanuts), maize, and tree nuts under warm and humid conditions. 1. **Why Aspergillus flavus is correct:** It is the primary source of Aflatoxin B1, B2, G1, and G2. Aflatoxin B1 is the most potent natural hepatocarcinogen. It acts by causing a specific mutation (G to T transversion) in the **p53 tumor suppressor gene** at codon 249, leading to **Hepatocellular Carcinoma (HCC)**. 2. **Analysis of Incorrect Options:** * **Aspergillus fumigatus:** This is the most common cause of invasive aspergillosis, aspergilloma ("fungus ball"), and ABPA (Allergic Bronchopulmonary Aspergillosis). It produces toxins like gliotoxin but not aflatoxin. * **Claviceps purpurea:** This fungus infects rye and cereal grains to produce **Ergot alkaloids**. Ingestion leads to Ergotism ("St. Anthony’s Fire"), characterized by intense vasoconstriction (gangrene) and hallucinations. * **Argemone mexicana:** This is a weed (Prickly Poppy). Its seeds contaminate mustard oil, leading to **Epidemic Dropsy** due to the toxin **Sanguinarine**. It is not a fungus. **High-Yield Clinical Pearls for NEET-PG:** * **Target Organ:** Liver (Acute toxicity causes hepatitis; chronic exposure causes HCC). * **Aflatoxin M1:** A metabolite of aflatoxin B1 found in the **milk** of animals that have consumed contaminated feed. * **Diagnosis:** Fluorescence under UV light is often used to detect contaminated grains. * **Synergy:** The risk of HCC increases significantly (up to 30-60 times) if a patient has co-existing **Hepatitis B (HBV)** infection.
Question 167: How is Pneumocystis jirovecii diagnosed?
- A. Microscopic examination of sputum for trophozoites and cysts (Correct Answer)
- B. Bacterial culture
- C. Positive serological tests
- D. Growth on artificial media
Explanation: **Explanation:** *Pneumocystis jirovecii* is a unique unicellular fungus that primarily causes opportunistic pneumonia (PCP) in immunocompromised individuals, particularly those with HIV/AIDS. **1. Why Option A is Correct:** *Pneumocystis jirovecii* **cannot be cultured** on routine artificial media. Therefore, diagnosis relies heavily on the direct microscopic visualization of the organism in clinical specimens. The specimens used include induced sputum, bronchoalveolar lavage (BAL), or lung biopsy. Microscopic examination identifies two main forms: * **Trophozoites:** Small, pleomorphic forms (best seen with Giemsa or Wright stain). * **Cysts:** Thick-walled, spherical structures containing intracystic bodies (best seen with **Gomori Methenamine Silver (GMS)** or Periodic Acid-Schiff (PAS) stains). **2. Why Other Options are Incorrect:** * **Option B & D:** *P. jirovecii* is an obligate parasite that lacks the metabolic pathways required for growth on bacterial or fungal artificial media (like Sabouraud Dextrose Agar). * **Option C:** Serological tests (detecting antibodies) are not clinically useful because most of the general population has been exposed to the fungus in childhood, leading to high seroprevalence without active disease. **3. NEET-PG High-Yield Pearls:** * **Specimen of Choice:** Bronchoalveolar Lavage (BAL) has a higher sensitivity (>90%) compared to induced sputum. * **Stains to Remember:** * **GMS Stain:** Gold standard for visualizing "crushed ping-pong ball" shaped cysts. * **Direct Fluorescent Antibody (DFA):** Highly sensitive and specific diagnostic method. * **Biomarker:** Elevated **(1,3)-beta-D-glucan** in serum is a highly sensitive (but non-specific) marker for PCP. * **Drug of Choice:** Trimethoprim-sulfamethoxazole (TMP-SMX).
Question 168: How many episodes of vulval candidiasis per year are needed for the diagnosis of recurrent vulvovaginal candidiasis?
- A. 1
- B. 2
- C. 3
- D. 4 (Correct Answer)
Explanation: **Explanation:** **Recurrent Vulvovaginal Candidiasis (RVVC)** is a specific clinical entity defined by the frequency of symptomatic episodes. According to the CDC and standard microbiological guidelines, the diagnosis requires **four or more episodes** of symptomatic vulvovaginal candidiasis within a **12-month period**. * **Why Option D is Correct:** The threshold of **4 episodes per year** is the globally accepted diagnostic criterion. RVVC affects approximately 5–8% of women of reproductive age and often involves *Candida albicans*, though non-albicans species (like *C. glabrata*) are more common in recurrent cases than in sporadic ones. * **Why Options A, B, and C are Incorrect:** * **1 episode:** This is considered "sporadic" or "uncomplicated" candidiasis. * **2 or 3 episodes:** While frequent, these do not meet the formal clinical definition of "recurrent" disease, which necessitates a more intensive treatment regimen (induction followed by long-term maintenance therapy). **High-Yield Clinical Pearls for NEET-PG:** * **Risk Factors:** Uncontrolled diabetes mellitus, pregnancy, and immunosuppression. However, most women with RVVC have no identifiable predisposing factors. * **Microscopy:** Look for **pseudohyphae and budding yeast** on KOH mount (except for *C. glabrata*, which only shows spores/blastoconidia). * **Treatment of RVVC:** Requires an induction phase (e.g., Fluconazole 150 mg every 72 hours for 3 doses) followed by a **maintenance phase** (Fluconazole 150 mg weekly for 6 months). * **Vaginal pH:** In candidiasis, the vaginal pH is typically **normal (<4.5)**, helping to differentiate it from Bacterial Vaginosis or Trichomoniasis where pH is >4.5.
Question 169: A patient with severe mycotic infection, diabetes mellitus, and cellulitis is suffering from which condition?
- A. Mucormycosis (Correct Answer)
- B. Histoplasmosis
- C. Candidiasis
- D. None of the above
Explanation: **Explanation:** The clinical triad of **severe mycotic infection, uncontrolled Diabetes Mellitus (DM), and cellulitis** (specifically facial or orbital) is a classic presentation of **Mucormycosis**. 1. **Why Mucormycosis is correct:** Mucormycosis (caused by fungi like *Rhizopus* and *Mucor*) is an opportunistic, angioinvasive infection. **Diabetes Mellitus**, especially with Ketoacidosis (DKA), is the most significant risk factor. The acidic environment and high glucose levels impair neutrophil chemotaxis and provide an ideal growth medium. The "cellulitis" mentioned refers to the rapid, necrotic spread in the rhino-orbital-cerebral region, often presenting as facial swelling or periorbital cellulitis that quickly progresses to black eschar formation due to vascular invasion and tissue infarction. 2. **Why other options are incorrect:** * **Histoplasmosis:** This is a systemic dimorphic fungal infection primarily involving the lungs (granulomatous disease). While it can occur in immunocompromised states, it is not classically associated with acute cellulitis or specifically triggered by DM in this manner. * **Candidiasis:** While common in diabetics, it usually presents as mucosal (thrush) or superficial skin infections (intertrigo). While systemic candidiasis exists, it does not typically present as the aggressive, necrotizing "cellulitis" described in acute mycotic emergencies. **High-Yield Clinical Pearls for NEET-PG:** * **Hallmark:** Broad, **non-septate hyphae** branching at **right angles (90°)**. * **Key Risk Factor:** DKA (Ketone reductase enzyme in *Rhizopus* allows it to thrive in acidic states). * **Treatment:** Surgical debridement + **Liposomal Amphotericin B** (Drug of choice). * **Imaging:** Look for "Reverse Halo Sign" on chest CT in pulmonary cases.
Question 170: Which of the following is the rarest opportunistic fungal infection seen in an AIDS patient?
- A. Cryptococcosis
- B. Candidiasis
- C. Histoplasmosis
- D. Aspergillosis (Correct Answer)
Explanation: **Explanation:** In the context of HIV/AIDS, the prevalence of opportunistic fungal infections is closely linked to the degree of immunosuppression (CD4 count). While many fungi thrive in T-cell deficient states, **Aspergillosis** is paradoxically the **rarest** among the listed options. **Why Aspergillosis is the correct answer:** The primary host defense against *Aspergillus* species is the **neutrophil** (via oxidative killing) and alveolar macrophages. Since HIV is primarily a disease of T-lymphocyte depletion rather than primary neutropenia, AIDS patients do not typically develop invasive aspergillosis unless they have additional risk factors such as profound neutropenia (from ganciclovir or chemotherapy) or corticosteroid use. **Analysis of incorrect options:** * **Candidiasis (B):** This is the **most common** opportunistic fungal infection in AIDS. Oropharyngeal candidiasis (thrush) occurs early (CD4 <200), while esophageal candidiasis is an AIDS-defining illness. * **Cryptococcosis (A):** Caused by *Cryptococcus neoformans*, this is the most common cause of fungal meningitis in AIDS patients (typically CD4 <100). * **Histoplasmosis (C):** In endemic areas, disseminated histoplasmosis is a frequent AIDS-defining illness occurring at CD4 counts <150. **NEET-PG High-Yield Pearls:** * **Most common fungal infection in AIDS:** Candidiasis. * **Most common life-threatening fungal infection in AIDS:** *Pneumocystis jirovecii* pneumonia (PCP). * **Most common fungal meningitis in AIDS:** Cryptococcosis (Diagnosis: India Ink, Mucicarmine stain, or CrAg Lateral Flow Assay). * **Aspergillus marker:** Galactomannan (cell wall component). * **Key takeaway:** If an AIDS patient has Aspergillosis, look for co-existing **neutropenia**.
Practice by Chapter
Classification of Fungi
Practice Questions
Superficial Mycoses
Practice Questions
Dermatophytes
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Subcutaneous Mycoses
Practice Questions
Candidiasis
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Aspergillosis
Practice Questions
Cryptococcosis
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Zygomycosis
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Endemic Mycoses
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Opportunistic Fungal Infections
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Antifungal Agents
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Laboratory Diagnosis of Fungal Infections
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