NEET-PG 2025 - Microbiology PYQs Practice Questions

Q: A patient presents with irregular swelling over the foot, multiple discharging sinuses, and black granules. A KOH mount is performed on the discharge. What is the most likely observation?

Slender dematiaceous fungi. ***Slender dematiaceous fungi*** - The clinical triad of irregular swelling, multiple discharging sinuses, and the presence of **black granules** strongly suggests **black-grained eumycetoma** (e.g., caused by *Madurella mycetomatis*). - KOH mount of the black granule reveals densely packed, brown-to-black pigmented (**dematiaceous**) septate hyphal elements and chlamydospores, consistent with slender dematiaceous fungi. *Arthrospores* - Arthrospores are typically seen in superficial infections like **dermatophytosis** (e.g., Tinea capitis, *Trichophyton*) or are characteristic of the parasitic phase of *Coccidioides immitis*. - They are not the primary microscopic finding within the tissue granule of mycetoma. *Yeast* - Yeast forms are characteristic of systemic infections like **Candidiasis**, Cryptococcosis, or Histoplasmosis, or are seen as sclerotic (Medlar) bodies in **Chromoblastomycosis**. - Mycetoma granules are formed by highly organized masses of filamentous hyphae, not unicellular yeast. *Septate hyphae 4-5* - This describes the general morphology and width of hyphae seen in common molds like **Aspergillus** or *Fusarium*. - This description is incomplete for black-grained mycetoma as it omits the distinctive feature of the fungus being pigmented (**dematiaceous**), which is critical for identifying the organism within the black granule. [Practice more Microbiology PYQs on OnCourse]

Q: A 5-year-old child presents with nocturnal perianal itching. The image below shows the organism identified on an adhesive tape test. What is the most likely causative agent?

Enterobius vermicularis. ***Enterobius vermicularis*** - The clinical presentation of **nocturnal perianal itching** (pruritus ani) in a child is highly characteristic of **pinworm infection** (enterobiasis). - The image shows a classic **D-shaped** or planoconvex egg, frequently found on the **adhesive tape test**, which are key identifiers for *Enterobius vermicularis*. *Ancylostoma duodenale* - This parasite causes **hookworm disease**, typically manifesting as **iron-deficiency anemia** and rarely perianal itching. - *Ancylostoma* eggs are oval, thin-shelled, and typically found in the **stool**, not via a tape test. *Hymenolepis nana* - This is the **dwarf tapeworm**, which usually causes mild or asymptomatic infection, though heavy infections can cause abdominal discomfort. - The eggs are small, oval, and possess **polar filaments** between the shell and the oncosphere, which are absent in the image. *Trichuris trichiura* - This parasite, the **whipworm**, causes trichuriasis, which presents with bloody diarrhea and occasionally **rectal prolapse** in heavy infections. - *Trichuris* eggs are distinctively **barrel-shaped** with two prominent bipolar mucoid plugs at each end. [Practice more Microbiology PYQs on OnCourse]

Q: A patient presents with a history of chronic meningitis. Laboratory findings show Gram-positive, filamentous branching bacteria, Positive ZN stain, Growth on paraffin bait culture. Which of the following is the most likely causative organism?

Nocardia asteroides. ***Nocardia asteroides*** - This organism is characterized by **Gram-positive, filamentous, branching bacteria** which are also typically **weakly acid-fast** (Positive ZN stain), differentiating it from Actinomyces. - The ability to utilize paraffin as a sole carbon source and grow on **paraffin bait culture** is a classical diagnostic method specifically employed for identifying **Nocardia** species, fitting the clinical picture of chronic meningitis (Nocardiosis). *Actinomyces israelii* - Although it is a **Gram-positive, filamentous, branching bacterium**, *Actinomyces* is strictly **anaerobic** and is typically **non-acid fast** (ZN negative), which contradicts the lab finding. - It commonly causes chronic suppurative infections like lumpy jaw, often involving **sulfur granules**, and is not diagnosed via paraffin culture methods. *Mycobacterium tuberculosis* - This organism is a major cause of **chronic meningitis** and is **strongly acid-fast** (ZN positive), but its morphology is that of a simple rod (**bacillus**), not a **filamentous branching** structure. - It requires specific media like **Lowenstein-Jensen (LJ) medium** for culture and is not known to grow on paraffin bait. *Cryptococcus neoformans* - This is an encapsulated **yeast (fungus)**, not a bacterium, and therefore does not show **filamentous branching** or Gram-positive bacterial morphology. - Diagnosis is typically made via **India ink stain** or detection of **Cryptococcal antigen** in CSF, not ZN staining or paraffin bait culture. [Practice more Microbiology PYQs on OnCourse]

Q: Group A Streptococcus is the most common cause of bacterial pharyngitis in school-aged children. Which of the following bacterial components is primarily responsible for its attachment to fibronectin on the epithelial lining of the pharynx?

Lipoteichoic acid. ***Lipoteichoic acid*** - **Lipoteichoic acid (LTA)**, along with the **M protein**, serves as a key adhesin for Group A Streptococcus, mediating attachment by binding to **fibronectin** receptors on pharyngeal epithelial cells. - This adherence mechanism is essential for the initial colonization and subsequent establishment of **streptococcal pharyngitis**. *Lipoprotein* - **Lipoproteins** are structurally diverse cell components, but they are not recognized as the primary molecular component mediating the specific attachment of GAS to **fibronectin**. - They often reside in the cell membrane and typically function in **nutrient transport** or signaling pathways. *Capsule* - The **hyaluronic acid capsule** of Group A Streptococcus mainly functions as an **anti-phagocytic factor** against host immune cells, preventing ingestion. - While important for virulence, it is not the molecule that directly facilitates initial adherence to the **fibronectin** layer of the host epithelium. *Flagella* - **Flagella** are organelles primarily responsible for **bacterial motility** (movement). - *Streptococcus pyogenes* (Group A Streptococcus) is a **non-motile** organism and therefore lacks flagella. [Practice more Microbiology PYQs on OnCourse]

Q: In a village, several people developed dysentery after consuming raw milk. On laboratory examination, gram-negative, curved rods with polymorphonuclear infiltration were found in stool samples. Which of the following is the most likely causative organism?

Campylobacter jejuni. ***Campylobacter jejuni*** - This organism is a **Gram-negative, curved or S-shaped rod** (seagull appearance) that causes inflammatory diarrhea (**dysentery**) and is the most common antecedent of **Guillain-Barré Syndrome**. - The association of dysentery with consumption of **raw milk** is a classic epidemiological feature of *C. jejuni* infection, explaining the outbreak. *Clostridium perfringens* - This is a **Gram-positive, spore-forming rod** and causes toxin-mediated food poisoning (Type A) characterized primarily by watery diarrhea, not typically dysentery. - The source is usually contaminated meat and gravies, and the stool sample would show a **Gram-positive rod**, not a curved Gram-negative rod. *Staphylococcus aureus* - This organism is a **Gram-positive coccus** that causes food intoxication with rapid onset vomiting being the prominent feature, not dysentery. - The pathology is preformed toxin-mediated, and stool analysis would reveal **cocci**, not curved rods, and lacks the PMN infiltration typical of dysentery. *Vibrio parahaemolyticus* - While it is a **Gram-negative curved rod**, it is strongly associated with the consumption of **raw or undercooked seafood**, especially shellfish. - Clinically, it usually causes watery diarrhea, and raw milk is not its typical vehicle of transmission for large outbreaks. [Practice more Microbiology PYQs on OnCourse]

Question 1

A patient presents with irregular swelling over the foot, multiple discharging sinuses, and black granules. A KOH mount is performed on the discharge. What is the most likely observation?

Accepted Answer

Slender dematiaceous fungi

Answer

Yeast

Answer

Septate hyphae 4-5

Answer

Arthrospores

Question 2

A 5-year-old child presents with nocturnal perianal itching. The image below shows the organism identified on an adhesive tape test. What is the most likely causative agent?

Accepted Answer

Enterobius vermicularis

Answer

Hymenolepis nana

Answer

Trichuris trichiura

Answer

Ancylostoma duodenale

Question 3

A patient presents with a history of chronic meningitis. Laboratory findings show Gram-positive, filamentous branching bacteria, Positive ZN stain, Growth on paraffin bait culture. Which of the following is the most likely causative organism?

Accepted Answer

Nocardia asteroides

Answer

Actinomyces israelii

Answer

Mycobacterium tuberculosis

Answer

Cryptococcus neoformans

Question 4

Group A Streptococcus is the most common cause of bacterial pharyngitis in school-aged children. Which of the following bacterial components is primarily responsible for its attachment to fibronectin on the epithelial lining of the pharynx?

Accepted Answer

Lipoteichoic acid

Answer

Capsule

Answer

Flagella

Answer

Lipoprotein

Question 5

In a village, several people developed dysentery after consuming raw milk. On laboratory examination, gram-negative, curved rods with polymorphonuclear infiltration were found in stool samples. Which of the following is the most likely causative organism?

Accepted Answer

Campylobacter jejuni

Answer

Staphylococcus aureus

Answer

Vibrio parahaemolyticus

Answer

Clostridium perfringens

Question 6

A patient presents with low-grade fever, chronic cough, and weight loss. Fungal culture from respiratory secretions shows the following organism with characteristic tuberculate macroconidia on microscopy. What is the most likely diagnosis?

Accepted Answer

Histoplasmosis

Answer

Cryptococcosis

Answer

Coccidioidomycosis

Answer

Blastomycosis

Question 7

A young adult presents with facial pain and painful vesicular lesions in the mouth. Tzanck smear reveals multinucleated giant cells with intranuclear inclusions. What is the most likely causative organism?

Accepted Answer

Herpes simplex virus

Answer

Adenovirus

Answer

Cytomegalovirus

Answer

Epstein-Barr virus

Question 8

A patient presents with recurrent infections with Neisseria gonorrhoeae. Which of the following investigations is most appropriate to evaluate the underlying immunodeficiency?

Accepted Answer

Terminal complement (C5-C9) assay

Answer

Nitroblue tetrazolium test

Answer

Quantitative immunoglobulin levels

Answer

C1 esterase inhibitor assay

Question 9

A farmer presents with an ulcerative skin lesion showing signs of necrosis. Smear from the ulcer stained with polychrome methylene blue reveals capsulated bacilli that are McFadyean reaction positive. What is the most likely causative organism?

Accepted Answer

Bacillus anthracis

Answer

Yersinia pestis

Answer

Francisella tularensis

Answer

Clostridium perfringens

Question 10

A middle-aged man from an endemic region presents with progressive swelling of the lower limb. A peripheral blood smear shows the following structure. What is the most likely cause of his limb swelling?

Accepted Answer

Lymphatic obstruction

Answer

Hypoalbuminemia

Answer

Hypoproteinemia

Answer

Increased hydrostatic pressure

NEET-PG 2025 — Microbiology