NEET-PG 2015 - Microbiology PYQs Practice Questions

Q: XDR-TB is defined as resistance to which of the following drug combinations?

Fluoroquinolones plus INH plus rifampicin plus amikacin. **Fluoroquinolones plus INH plus rifampicin plus amikacin** - **Extensively drug-resistant tuberculosis (XDR-TB)** is defined by resistance to the most effective anti-TB drugs: **isoniazid (INH)**, **rifampicin**, any **fluoroquinolone**, and at least one of the three injectable second-line drugs (**amikacin**, **kanamycin**, or **capreomycin**). - This combination signifies a substantial therapeutic challenge due to limited treatment options and a high risk of treatment failure. *INH plus rifampicin* - Resistance to **INH** and **rifampicin** defines **multidrug-resistant tuberculosis (MDR-TB)**, which is a precursor to XDR-TB but not XDR-TB itself. - While serious, MDR-TB is not as extensively resistant as XDR-TB, as it doesn't include resistance to fluoroquinolones and second-line injectables. *Fluoroquinolones plus INH plus amikacin* - This combination is incomplete for the definition of XDR-TB because it omits **rifampicin** from the core definition. - XDR-TB specifically requires resistance to both **INH** and **rifampicin** (defining MDR-TB), in addition to resistance to a fluoroquinolone and one of the injectable second-line drugs. *Fluoroquinolones plus rifampicin plus kanamycin* - This combination is also incomplete for the definition of XDR-TB as it omits **isoniazid (INH)**, which is one of the two most crucial first-line drugs that characterize MDR-TB. - XDR-TB builds upon MDR-TB's resistance to both INH and rifampicin. [Practice more Microbiology PYQs on OnCourse]

Q: Interleukin 2 is produced by

T helper cells 1. ***T helper cells 1*** - **T helper 1 (Th1) cells** are a primary source of **interleukin-2 (IL-2)**, which is crucial for the proliferation and survival of T cells. - IL-2 acts as a **T-cell growth factor**, promoting the expansion of activated T cells, including cytotoxic T lymphocytes. *T helper cells 2* - **T helper 2 (Th2) cells** primarily produce cytokines like **IL-4, IL-5, IL-6, IL-10, and IL-13**, which are involved in humoral immunity and allergic responses. - While Th2 cells are important for immune responses, they are not major producers of IL-2. *Natural killer cells* - **Natural killer (NK) cells** are part of the innate immune system and produce cytokines such as **interferon-gamma (IFN-$\gamma$)** and **tumor necrosis factor-alpha (TNF-$\alpha$)**. - They are not a significant source of IL-2, which is primarily a T-cell derived growth factor. *Basophils* - **Basophils** are granulocytes involved in allergic reactions and anti-parasitic immunity, producing mediators like **histamine** and cytokines such as **IL-4** and **IL-13**. - Basophils do not produce IL-2; their role is distinct in the immune response compared to T cells. [Practice more Microbiology PYQs on OnCourse]

Q: The process by which antigen-specific B lymphocytes are selected and activated to proliferate and produce antibodies is called:

Clonal selection. ***Clonal selection*** - **Clonal selection** is the fundamental process by which an antigen-specific B lymphocyte is **selected** when its B cell receptor (BCR) recognizes and binds to a matching antigen. - This binding triggers the B cell to become **activated**, **proliferate** (undergo clonal expansion), and **differentiate** into plasma cells that produce antibodies specific to that antigen. - This process is the cornerstone of **adaptive immunity**, ensuring that only B cells with receptors matching the encountered antigen are stimulated to respond. *Class switching* - **Class switching** (isotype switching) occurs AFTER clonal selection and activation. - It allows already-activated B cells to change the **antibody class** they produce (from IgM to IgG, IgA, or IgE) while maintaining the **same antigen specificity**. - This process modifies effector functions but does NOT involve the initial selection and activation of antigen-specific B cells. *Group switching* - This is not a recognized term in immunology. - It does not describe any standard process of B cell activation or antibody production. *Hybridisation* - **Hybridization** refers to the formation of double-stranded nucleic acids from complementary strands or the creation of hybrid cells (e.g., hybridomas for monoclonal antibody production). - It is not the physiological process by which B lymphocytes are selected and activated in response to antigen exposure. [Practice more Microbiology PYQs on OnCourse]

Q: IFN-gamma is produced by

T-cells. ***T-cells*** - **Interferon-gamma (IFN-γ)** is a crucial cytokine primarily produced by **activated T-lymphocytes**, especially **Th1 cells** and **cytotoxic T lymphocytes (CTLs)**. - Natural killer (NK) cells also produce **IFN-γ**, which plays a key role in **antiviral** and **antitumor immunity**, as well as in promoting **Type 1 immune responses**. *Macrophages* - While macrophages are **responsive to IFN-γ** (e.g., becoming activated), they are not the primary producers of this cytokine. - Macrophages primarily produce other cytokines such as **IL-1, IL-6, TNF-alpha**, and **IL-12** in response to infection or inflammation. *Neutrophils* - **Neutrophils** are key phagocytes in the innate immune system and are primarily involved in engulfing and killing pathogens. - They are not known to be a significant source of **IFN-γ** production; their main defensive mechanisms involve **phagocytosis**, **degranulation**, and **NETosis**. *B-cells* - **B-cells** are central to humoral immunity, specializing in **antibody production** and acting as **antigen-presenting cells**. - They generally do not produce **IFN-γ**; instead, their cytokine repertoire includes **IL-10**, **IL-6**, and **lymphotoxin**. [Practice more Microbiology PYQs on OnCourse]

Q: "Citron bodies" are boat- or leaf-shaped pleomorphic organisms found in exudates. This is a characteristic feature of which organism?

Cl. septicum. ***Cl. septicum*** - *Clostridium septicum* characteristically forms **"Citron bodies"** - boat-shaped or leaf-shaped pleomorphic organisms in exudates - These spindle-shaped, cigar-like forms are a **distinctive morphological feature** of this organism - Associated with **gas gangrene** and spontaneous myonecrosis, particularly in patients with underlying malignancy or neutropenia - The pleomorphic morphology distinguishes it from other clostridial species *Cl. welchii* - *Clostridium perfringens* (formerly *Cl. welchii*) appears as **large, rectangular, "boxcar-shaped" Gram-positive rods** - Does **not** form citron bodies or show the characteristic boat/leaf-shaped pleomorphism - Most common cause of gas gangrene but has different morphological appearance *Cl. edematiens* - *Clostridium oedematiens* (now *Clostridium novyi*) appears as **large, Gram-positive rods** with subterminal spores - Does not form citron bodies - Associated with gas gangrene but lacks the pleomorphic morphology described *Cl. tetani* - *Clostridium tetani* has characteristic **terminal spores** giving a "drumstick" or "tennis racket" appearance - Does not form citron bodies or pleomorphic shapes - Morphologically distinct with its terminal spore appearance [Practice more Microbiology PYQs on OnCourse]

Question 1

XDR-TB is defined as resistance to which of the following drug combinations?

Accepted Answer

Fluoroquinolones plus INH plus rifampicin plus amikacin

Answer

INH plus rifampicin

Answer

Fluoroquinolones plus INH plus amikacin

Answer

Fluoroquinolones plus rifampicin plus kanamycin

Question 2

Interleukin 2 is produced by

Accepted Answer

T helper cells 1

Answer

T helper cells 2

Answer

Natural killer cells

Answer

Basophils

Question 3

The process by which antigen-specific B lymphocytes are selected and activated to proliferate and produce antibodies is called:

Accepted Answer

Clonal selection

Answer

Class switching

Answer

Group switching

Answer

Hybridisation

Question 4

IFN-gamma is produced by

Accepted Answer

T-cells

Answer

Macrophages

Answer

Neutrophils

Answer

B-cells

Question 5

"Citron bodies" are boat- or leaf-shaped pleomorphic organisms found in exudates. This is a characteristic feature of which organism?

Accepted Answer

Cl. septicum

Answer

Cl. edematiens

Answer

Cl. tetani

Answer

Cl. welchii

Question 6

In the context of immune response, which of the following cell types does not express MHC class II molecules?

Accepted Answer

NK cells

Answer

Cortical macrophages

Answer

Neutrophils

Answer

Medullary macrophages

Question 7

What is the Hib conjugate vaccine made of?

Accepted Answer

Capsular polysaccharide with carrier

Answer

Capsular polysaccharide

Answer

Purified protein with carrier

Answer

Cell wall polysaccharide

Question 8

Capsular polysaccharide derived vaccine is available for all meningococci except?

Accepted Answer

Group B

Answer

Group C

Answer

Group Y

Answer

Group A

Question 9

Most common route of nosocomial infection [Hospital-acquired infection]?

Accepted Answer

Direct contact

Answer

Droplet transmission

Answer

Indirect contact

Answer

Vehicle transmission

Question 10

In Rideal-Walker method, plates are incubated for?

Accepted Answer

2-3 days

Answer

Less than 2 days

Answer

6 to 8 days

Answer

More than 10 days

NEET-PG 2015 — Microbiology