INI-CET 2024 - Microbiology PYQs Practice Questions

Q: HBsAg is based on which principle

ELISA. ***ELISA*** - **Enzyme-linked immunosorbent assay (ELISA)** is a widely used laboratory test to detect and quantify antigens (like HBsAg) or antibodies in a sample. - It involves an enzyme-linked antibody that reacts with a substrate to produce a detectable signal, making it highly sensitive and specific for **HBsAg detection**. *Immunochromatography assays* - These are typically **rapid diagnostic tests (RDTs)** that provide quick qualitative results, often used for point-of-care testing. - While they can detect HBsAg, they generally have lower sensitivity and specificity compared to ELISA. *Chemiluminescence* - This is a detection method used in some immunoassays where a chemical reaction emits light, often providing higher sensitivity than colorimetric detection. - While it can be incorporated into HBsAg testing platforms, it is a *detection principle* rather than the primary assay principle like ELISA itself. *Immunofluorescence* - This technique uses **fluorescently labeled antibodies** to visualize antigens in cells or tissues under a fluorescence microscope [1]. - It is used for localization and identification of antigens, but not typically the primary method for routine quantitative HBsAg serology [1]. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 259-260. [Practice more Microbiology PYQs on OnCourse]

Q: A 6-year-old boy presents with fever and chills, cough, rapid breathing, difficulty breathing, and chest pain. A culture from a respiratory sample shows Gram-positive bacteria. What is the most likely organism causing this infection?

Streptococcus pneumoniae. ***Streptococcus pneumoniae*** - This clinical picture describes typical symptoms of **pneumonia** in a child, including fever, cough, rapid and difficult breathing, and chest pain. - **_Streptococcus pneumoniae_** is the most common bacterial cause of community-acquired pneumonia in children. The respiratory sample showing gram-positive bacteria further supports this. *Staphylococcus aureus* - While **_Staphylococcus aureus_** can cause pneumonia, it is less common than _Streptococcus pneumoniae_ in community-acquired cases in healthy children and often associated with more severe, necrotizing forms or post-viral infections. - While it is a **Gram-positive bacterium**, its clinical presentation would not be the most likely first choice for typical pneumonia symptoms in this age group. *Propionibacterium acnes* - **_Propionibacterium acnes_** (now *Cutibacterium acnes*) is primarily associated with **acne vulgaris** and, less commonly, opportunistic infections related to implanted devices or some rare soft tissue infections. - It is not a typical cause of primary respiratory infections like pneumonia. *Streptococcus pyogenes* - **_Streptococcus pyogenes_** (Group A Streptococcus) is known for causing **pharyngitis** (strep throat), skin infections (impetigo, cellulitis), and scarlet fever. - While it can rarely cause pneumonia, it is not a common cause, and the constellation of symptoms points more strongly to _Streptococcus pneumoniae_. [Practice more Microbiology PYQs on OnCourse]

Q: What is the best investigation for identifying malaria species?

Thin smear with Giemsa. ***Thin smear with Giemsa*** - A **thin smear** allows for the visualization of **parasite morphology** within red blood cells, which is crucial for distinguishing between species of *Plasmodium*. - **Giemsa stain** provides optimal contrast for identifying characteristic features such as **merozoites**, **trophozoites**, **schizonts**, and **gametocytes** of different malaria species. *Thick smear* - A **thick smear** is primarily used for **detecting the presence of malaria parasites** and for quantifying parasite density due to its higher sensitivity. - However, because red blood cells are lysed, it **does not preserve parasite morphology** well, making species identification difficult. *QBC* - **Quantitative Buffy Coat (QBC) analysis** is a rapid method for detecting malaria parasites based on their fluorescence under UV light. - While sensitive for detection, it generally **does not allow for precise species identification** due to the lack of clear morphological detail. *Thin smear with acridine orange* - A **thin smear stained with acridine orange** is used for rapid detection of parasites by fluorescence microscopy. - Similar to QBC, it is **less effective for detailed morphological examination** and specific species identification compared to Giemsa-stained thin smears. [Practice more Microbiology PYQs on OnCourse]

Q: Which of the following organisms show parthenogenesis?

Strongyloides. ***Correct: Strongyloides*** - *Strongyloides stercoralis* is known for its complex life cycle, which includes **parthenogenetic reproduction** in the free-living female generation. - The parasitic females can produce larvae directly through **parthenogenesis (reproduction without fertilization)**, enabling autoinfection. - This unique ability allows the parasite to **reproduce without a male** within and outside the human host, leading to persistent infections and hyperinfection syndrome. *Incorrect: Ascaris* - *Ascaris lumbricoides* reproduces sexually, requiring **both male and female worms** for fertilization and egg production. - There is no evidence of parthenogenetic reproduction in *Ascaris*. *Incorrect: Trichuris* - *Trichuris trichiura* (whipworm) is a **dioecious** (sexually reproducing) nematode where **separate male and female worms** are required for reproduction. - Parthenogenesis is not observed in the life cycle of *Trichuris*. *Incorrect: Ancylostoma* - *Ancylostoma duodenale* (hookworm) reproduces sexually in the human intestine. - Requires **male and female worms** to produce fertilized eggs; parthenogenesis does not occur. [Practice more Microbiology PYQs on OnCourse]

Q: A lady came with yellowish discharge and stain showing gram-negative diplococci. What is the most likely causative organism of her condition?

Neisseria gonorrhoeae. ***Neisseria gonorrhoeae*** - The presence of **yellowish discharge** and **gram-negative diplococci** on a stain is a classic presentation for **gonorrhea**, caused by *Neisseria gonorrhoeae*. - This bacterium is a common cause of **sexually transmitted infections (STIs)**, leading to conditions like cervicitis, urethritis, and pelvic inflammatory disease. *Streptococcus pneumoniae* - This organism is a **gram-positive coccus** and typically causes **respiratory infections** (e.g., pneumonia, otitis media, meningitis), not genital discharge with gram-negative diplococci. - It is not associated with STI-related yellowish genital discharge. *Enterococcus faecalis* - This is a **gram-positive coccus** and a common cause of **urinary tract infections (UTIs)** and **nosocomial infections**, but not typically associated with yellowish genital discharge showing gram-negative diplococci. - It is also not classified as a gram-negative organism. *Both Streptococcus and Enterococcus* - This option is incorrect because both *Streptococcus* and *Enterococcus* are **gram-positive organisms**. - The clinical presentation clearly describes **gram-negative diplococci**, which rules out these bacteria as the primary cause. [Practice more Microbiology PYQs on OnCourse]

Question 1

HBsAg is based on which principle

Accepted Answer

ELISA

Answer

Chemiluminescence

Answer

Immunofluorescence

Answer

Immunochromatography assays

Question 2

A 6-year-old boy presents with fever and chills, cough, rapid breathing, difficulty breathing, and chest pain. A culture from a respiratory sample shows Gram-positive bacteria. What is the most likely organism causing this infection?

Accepted Answer

Streptococcus pneumoniae

Answer

Streptococcus pyogenes

Answer

Staphylococcus aureus

Answer

Propionibacterium acnes

Question 3

What is the best investigation for identifying malaria species?

Accepted Answer

Thin smear with Giemsa

Answer

Thick smear

Answer

QBC

Answer

Thin smear with acridine orange

Question 4

Which of the following organisms show parthenogenesis?

Accepted Answer

Strongyloides

Answer

Ascaris

Answer

Trichuris

Answer

Ancylostoma

Question 5

A lady came with yellowish discharge and stain showing gram-negative diplococci. What is the most likely causative organism of her condition?

Accepted Answer

Neisseria gonorrhoeae

Answer

Streptococcus pneumoniae

Answer

Enterococcus faecalis

Answer

Both Streptococcus and Enterococcus

Question 6

Assertion: Plasmodium falciparum does not show the schizont stage in the peripheral blood. Reason: This is due to cytoadherence of infected RBCs to the vascular endothelium.

Accepted Answer

Assertion is true, reason is true and reason is the correct explanation of the assertion.

Answer

Assertion is true, reason is true but reason is not the correct explanation of the assertion.

Answer

Assertion is true, reason is false.

Answer

Assertion is false, reason is true.

Question 7

A patient presents with fever and retro-orbital pain. Which investigation should be conducted next for confirmation of dengue fever?

Accepted Answer

NS1 antigen test

Answer

Viral culture

Answer

IgM ELISA

Answer

PCR

Question 8

Which of the following organisms does not have a polysaccharide capsule?

Accepted Answer

Hepatitis B

Answer

Haemophilus influenzae type b (Hib)

Answer

Streptococcus pneumoniae (Pneumococcus)

Answer

Neisseria meningitidis

Question 9

Which of the following is not a polysaccharide vaccine?

Accepted Answer

Hepatitis B vaccine

Answer

Pneumococcal vaccine

Answer

Meningococcal vaccine

Answer

H. Influenzae B vaccine

Question 10

Assertion: Myocarditis is seen as a complication in faucial diphtheria. Reason: It is due to the exotoxin produced by Corynebacterium diphtheriae.

Accepted Answer

Assertion is true, reason is true and reason is the correct explanation of the assertion.

Answer

Assertion is false, reason is true.

Answer

Assertion is true, reason is true but reason is not the correct explanation of the assertion.

Answer

Assertion is true, reason is true.

INI-CET 2024 — Microbiology