INI-CET 2022 - Microbiology PYQs Practice Questions

Q: Affinity maturation of antibodies is because of _____ .

Somatic hypermutation. ***Somatic hypermutation*** - **Somatic hypermutation** is a process that introduces point mutations in the **variable regions** of immunoglobulin genes, primarily in B cells. - These mutations lead to the production of B cells with slightly altered **antibody affinities**, allowing for selection of those with higher affinity for the antigen. *Gene rearrangements* - **Gene rearrangements**, specifically **V(D)J recombination**, are responsible for the initial diversity of antibody specificities in immature B cells. - This process determines the basic antigen-binding site but does not fine-tune the **affinity** after initial antigen exposure. *CD40* - **CD40** is a co-stimulatory molecule on B cells that binds to **CD40L** on T cells, crucial for B cell activation, **isotype switching**, and germinal center formation. - While essential for antibody responses and germinal center reactions where affinity maturation occurs, **CD40** itself does not directly cause the molecular changes that lead to affinity maturation. *Differential mRNA processing* - **Differential mRNA processing** (or alternative splicing) primarily controls the production of different protein isoforms from a single gene. - In the context of antibodies, it can determine whether a B cell produces **membrane-bound** or **secreted** forms of antibodies, but it does not enhance the antigen-binding affinity. [Practice more Microbiology PYQs on OnCourse]

Q: Antigen presented on MHC class I molecules activates which of the following cells?

Cytotoxic T cells. ***Cytotoxic T cells*** - **MHC class I** molecules present **intracellular antigens** (e.g., viral or tumor antigens) to **CD8+ T cells** (cytotoxic T cells). - This binding activates the cytotoxic T cells, leading to the destruction of the **infected** or **abnormal host cell**. *NK cells* - **Natural Killer (NK) cells** recognize and kill target cells that have **reduced or absent MHC class I** expression, which often occurs in virally infected or tumor cells, not cells presenting antigens on MHC class I. - They are part of the **innate immune system** and do not require prior sensitization or MHC-peptide presentation for activation. *Helper cells* - **Helper T cells** (CD4+ T cells) recognize antigens presented on **MHC class II** molecules, typically expressed by **antigen-presenting cells** (APCs) like macrophages, B cells, and dendritic cells. - Their primary role is to **orchestrate immune responses** by releasing cytokines. *B cells* - **B cells** are primarily involved in **humoral immunity**, producing antibodies after recognizing specific antigens directly via their B cell receptors or with T cell help. - While they can present antigens on **MHC class II** to helper T cells, direct antigen binding to **MHC class I** does not activate B cells. [Practice more Microbiology PYQs on OnCourse]

Q: Which of the following statements regarding the given image is correct?

Majority of infections are asymptomatic in humans. ***Majority of infections are asymptomatic in humans*** - The image depicts an egg of *Hymenolepis nana*, also known as the **dwarf tapeworm**, identifiable by its characteristic **polar filaments** and **polar thickenings** on the inner membrane. - While heavy infections can cause symptoms, most *Hymenolepis nana* infections are **asymptomatic** or present with only mild, nonspecific gastrointestinal complaints. *Infection is acquired by ingestion of undercooked freshwater fish* - Infection with *Hymenolepis nana* is typically acquired through the **ingestion of eggs** directly from contaminated food or water, or via **fecally-contaminated hands**. - Ingestion of undercooked freshwater fish is associated with trematode (fluke) infections like **Clonorchis sinensis** or **Opisthorchis viverrini**, not *Hymenolepis nana*. *Albendazole is the drug of choice* - The drug of choice for *Hymenolepis nana* infection is **Praziquantel**, given as a single dose. - While albendazole might be used for some helminth infections, it is **less effective** than praziquantel for *Hymenolepis nana*. *It is the largest tapeworm infecting humans* - *Hymenolepis nana* is known as the **dwarf tapeworm** and is generally the **smallest tapeworm** that infects humans, typically measuring a few centimeters in length. - The largest tapeworm infecting humans is *Diphyllobothrium latum* (fish tapeworm), which can reach lengths of several meters. [Practice more Microbiology PYQs on OnCourse]

Q: Which of the following are acid-fast staining organisms? 1. Nocardia 2. Mycobacterium leprae 3. Actinomyces 4. Cryptosporidium parvum 5. Isospora belli

1,2,4,5. ***1,2,4,5*** - **Nocardia**, **Mycobacterium leprae**, **Cryptosporidium parvum**, and **Isospora belli** all exhibit acid-fast properties, meaning they retain carbolfuchsin stain even after decolorization with acid alcohol due to the presence of mycolic acid in their cell walls or unique cyst structures. - This characteristic is crucial for their identification in clinical microbiology and distinguishes them from many other microorganisms. *1,2,3* - This option incorrectly includes **Actinomyces** as an acid-fast organism. **Actinomyces** are Gram-positive, filamentous bacteria that are **not acid-fast**. - While Nocardia and Mycobacterium leprae are acid-fast, the inclusion of Actinomyces makes this choice incorrect. *1,2,3,4,5* - This option is incorrect because it includes **Actinomyces** as an acid-fast organism, which is not true. - **Actinomyces** are Gram-positive, non-acid-fast bacteria, differentiating them from the other listed organisms that do possess acid-fast properties. *3,4,5* - This option is incorrect because it excludes **Nocardia** and **Mycobacterium leprae**, both of which are prominent acid-fast organisms. - While Cryptosporidium parvum and Isospora belli are acid-fast, the omission of Nocardia and Mycobacterium leprae makes this answer incomplete and incorrect. [Practice more Microbiology PYQs on OnCourse]

Question 1

Affinity maturation of antibodies is because of _____ .

Accepted Answer

Somatic hypermutation

Answer

Gene rearrangements

Answer

CD40

Answer

Differential mRNA processing

Question 2

Antigen presented on MHC class I molecules activates which of the following cells?

Accepted Answer

Cytotoxic T cells

Answer

NK cells

Answer

Helper cells

Answer

B cells

Question 3

Which of the following is true about anti-CMV IgG antibodies?

Accepted Answer

IgG avidity assay helps in differentiating past and primary infection

Answer

Denotes latent CMV infection

Answer

Denotes chronic CMV infection with immunity to other serotypes

Answer

Indicates acute CMV infection

Question 4

Which of the following statements regarding the given image is correct?

Accepted Answer

Majority of infections are asymptomatic in humans

Answer

Albendazole is the drug of choice

Answer

Infection is acquired by ingestion of undercooked freshwater fish

Answer

It is the largest tapeworm infecting humans

Question 5

Which of the following are acid-fast staining organisms?

1. Nocardia
2. Mycobacterium leprae
3. Actinomyces
4. Cryptosporidium parvum
5. Isospora belli

Accepted Answer

1,2,4,5

Answer

1,2,3

Answer

1,2,3,4,5

Answer

3,4,5

Question 6

A young man presents with skin lesions as shown in the image below. All of the following organisms can spread through dermal and subcutaneous lymphatics, except

Accepted Answer

Staphylococcus aureus

Answer

Sporothrix schenckii

Answer

Nocardia asteroides

Answer

Mycobacterium marinum

Question 7

Which virus can be identified by a PCR method and is endemic to India?

Accepted Answer

Chikungunya virus

Answer

Ebola virus

Answer

Yellow fever

Answer

Hendra virus

Question 8

Which of the following is a gram-positive organism that shows the following appearance on Ziehl-Neelsen staining?

Accepted Answer

Nocardia

Answer

Mycobacterium tuberculosis

Answer

Actinomyces

Answer

Rhodococcus

Question 9

A forest worker developed skin lesions over the forearm, which initially started as macules but then became nodules. Histology of the nodule shows the following findings. Which of the following is true regarding this condition?

Accepted Answer

It is a dematiaceous fungus

Answer

Angioinvasion is common especially in people with hemolytic anemia

Answer

These bodies are formed by engulfment of the dead fungi by the macrophages

Answer

Infection commonly spreads to involve tendon, muscle and bone

Question 10

The viruses of the Filoviridae family like Ebola and Marburg resemble which of the following morphologies?

Accepted Answer

Filamentous

Answer

Brick shaped

Answer

Bullet shaped

Answer

Spherical

INI-CET 2022 — Microbiology