NEET-PG 2015 - Microbiology Practice Questions

Q: In the context of diagnosing syphilis, which of the following is an example of a precipitation test?

Kahn test. ***Kahn test*** - The Kahn test is a **flocculation** or **precipitation** test used for diagnosing syphilis. - It detects **reagin antibodies** in the patient's serum that react with a non-treponemal antigen (cardiolipin antigen). *Rose waaler test* - The Rose Waaler test is an **agglutination test** used to detect **rheumatoid factor** in patients with rheumatoid arthritis, not syphilis. - It involves sheep red blood cells sensitized with rabbit anti-sheep erythrocyte antibody. *Widal test* - The Widal test is an **agglutination test** used for the diagnosis of **typhoid fever**, detecting antibodies against *Salmonella* O and H antigens. - It is not used for the diagnosis of syphilis. *Latex agglutination* - Latex agglutination is a general type of **agglutination test** where antigen or antibody is coated onto latex particles. - While used in various diagnoses, it is not a specific precipitation test for syphilis in the context of classic methods like the Kahn test.

Q: Haptens are immunogenic when they covalently bind to which type of carrier?

Protein carrier. ***Protein carrier*** - Haptens are small molecules that are **antigenic** but not **immunogenic** on their own; they acquire immunogenicity when covalently bound to a larger carrier molecule. - **Proteins** are highly effective carriers because their complex structures and multiple epitopes can induce strong T-cell help, which is crucial for a robust antibody response against the hapten. *Lipid carrier* - While some lipids can be antigenic (e.g., glycolipids), they generally do not serve as effective carriers for haptens to induce a strong adaptive immune response, especially T-cell-dependent responses. - **Lipids** are less likely to be processed and presented by MHC molecules in a way that generates potent helper T-cell activation. *Polysaccharide carrier* - Some polysaccharides can be immunogenic themselves (e.g., bacterial capsular polysaccharides) and can induce T-cell-independent antibody responses. - However, for haptens to become immunogenic and induce a **T-cell-dependent antibody response**, a protein carrier is typically required. *None of the above carrier* - This option is incorrect because haptens do require a carrier to become immunogenic, and specific types of carriers are more effective than others. - The type of carrier chosen significantly impacts the **strength and nature of the immune response** to the hapten.

Q: Which human IgG subclass has the highest serum concentration?

IgG1. ***IgG1*** - **IgG1** constitutes approximately **60-70%** of the total IgG in human serum, making it the most abundant subclass. - Its high concentration reflects its crucial role in **neutralizing toxins**, agglutinating viruses, and opsonizing bacteria for phagocytosis. *IgG2* - **IgG2** makes up about **20-30%** of total IgG and is primarily important in protecting against **polysaccharide-encapsulated bacteria**. - While significant, its serum concentration is notably lower than that of IgG1. *IgG3* - **IgG3** is the least abundant IgG subclass, accounting for only **5-8%** of total IgG, and is characterized by a shorter half-life. - Despite its low concentration, it is highly efficient in activating the **complement system** due to its flexible hinge region. *IgG4* - **IgG4** comprises approximately **3-6%** of total IgG and is unique for its ability to undergo **Fab arm exchange**, leading to bispecific antibodies. - It does not activate complement and is often associated with allergy and protection against parasitic infections, but its concentration is significantly less than IgG1.

Q: Which of the following does not stimulate active immunity?

Transplacental antibody transfer in newborn. ***Transplacental antibody transfer in newborn*** - This is a form of **passive immunity**, where pre-formed **antibodies from the mother** are transferred to the newborn, providing immediate but temporary protection. - It does not involve the newborn's own immune system generating an immune response or creating **memory cells**. *Subclinical infection* - Even without overt symptoms, a **natural infection** exposes the immune system to pathogens, triggering an active immune response and generating **memory cells**. - This leads to **long-term immunity** against future exposures to the same pathogen. *Clinical infection* - A **symptomatic natural infection** involves the immune system actively responding to the pathogen, producing antibodies and **memory cells**. - This process is the basis of **naturally acquired active immunity** and provides durable protection. *Vaccination* - Vaccines contain weakened or inactive forms of pathogens, or their components, which stimulate the immune system to produce **antibodies** and **memory cells** without causing disease. - This is an example of **artificially acquired active immunity**, providing long-lasting protection.

Q: Which of the following is a specific feature of acquired immunity?

Immunological memory. ***Immunological memory*** - A key characteristic of **acquired immunity** is the ability to "remember" previous encounters with specific pathogens. - This memory leads to a more rapid and robust immune response upon subsequent exposure to the same pathogen. - This is the **defining feature** that distinguishes acquired immunity from innate immunity. *Affected by genetic makeup* - While genetic makeup can influence the *efficiency* of the acquired immune system, it is not a **specific feature** that distinguishes it from innate immunity. - **Both innate and acquired immunity** are affected by genetic factors, determining baseline resistance and immune response capability. *No antigen exposure* - **Acquired immunity** is specifically characterized by its *dependence* on antigen exposure to develop specific responses. - The phrase "no antigen exposure" describes how the **innate immune system** functions, providing immediate, non-specific protection without prior contact with a pathogen. *Immediate response* - **Innate immunity** provides an immediate, non-specific response to pathogens. - **Acquired immunity** takes time to develop (days to weeks) after initial antigen exposure, but provides a faster response upon re-exposure due to immunological memory.

Q: Lattice phenomenon is seen in which of the following?

Precipitation test. ***Precipitation test*** - The **lattice phenomenon** describes the formation of an interconnected network of antigen-antibody complexes, which is essential for visible precipitation to occur. - This phenomenon dictates that optimal precipitation requires a specific **antigen-to-antibody ratio**; an excess of either can lead to false-negative results due to soluble immune complexes (prozone or postzone effects). *Complement fixation test* - This test relies on the **binding of complement** to antigen-antibody complexes, leading to the lysis of indicator red blood cells if complement is not fixed. - It is a **two-stage test** that measures the consumption of complement, not the direct observation of a lattice. *None of the options* - This option is incorrect because the **precipitation test** clearly demonstrates the lattice phenomenon. - The formation of a visible precipitate is a direct result of antigen-antibody lattice formation. *Neutralization reaction* - Neutralization involves antibodies binding to toxins or viruses, **blocking their biological activity** rather than forming a visible precipitate. - It is a **functional assay** that measures the ability of antibodies to inhibit harmful effects, not the formation of large immune complexes.

Q: To which part of an antigen do monoclonal antibodies specifically bind?

Specific epitope on the antigen. ***Specific epitope on the antigen*** - Monoclonal antibodies are designed to recognize and bind to a **unique, specific region** on an antigen, known as an **epitope**. - This high specificity is crucial for their clinical applications, such as targeted therapies and diagnostic tests. *Both the epitope and the paratope* - The **epitope** is the part of the antigen, while the **paratope** is the part of the antibody that binds to the epitope. - An antibody binds to an epitope, not to both itself and its own binding site. *None of the options* - This option is incorrect because there is a correct answer among the choices provided, which accurately describes the binding site of monoclonal antibodies. *Part of the antibody that binds to the epitope* - This describes the **paratope**, which is the antigen-binding site on the antibody, not the part of the antigen to which the antibody binds. - The question specifically asks about the part of the antigen.

Q: What type of immunity is primarily associated with the administration of transfer factor?

Adoptive immunity. ***Adoptive immunity (Correct)*** - **Transfer factor** consists of small, dialyzable molecules extracted from immune T lymphocytes of an immune donor - Its administration transfers **cell-mediated immunity** from donor to recipient, which defines adoptive immunity - This represents transfer of **immune cells or their products** (not antibodies), providing antigen-specific cellular immunity - Also called **adoptive immunotherapy** or adoptive transfer *Artificial passive immunity (Incorrect)* - Involves the **transfer of pre-formed antibodies** (e.g., antitoxins, immunoglobulins, antiserum) from an immune individual or animal - Provides **immediate but temporary humoral protection** - Does NOT transfer cellular immunity - this is the key distinction from adoptive immunity - Examples: Anti-rabies immunoglobulin, anti-tetanus serum *Natural active immunity (Incorrect)* - Occurs when an individual is **naturally exposed to an antigen** (infection) and produces their own antibodies and immune cells - The host's own immune system **actively responds** to develop long-lasting immunity - Example: Immunity after recovering from measles or chickenpox *Artificial active immunity (Incorrect)* - Achieved through **vaccination** with attenuated, inactivated, or subunit antigens - The recipient's body is **actively stimulated** to produce protective immunity - Provides long-lasting protection through immunological memory

Q: Which of the following tests is not classified as an in vivo test?

Elek's gel precipitation test. ***Elek's gel precipitation test*** - This test is an **in vitro** method used to detect the production of **diphtheria toxin** by *Corynebacterium diphtheriae* strains in a lab setting, not within a living organism. - It involves the precipitation of toxin and antitoxin in an agar gel, forming visible lines. *Schick test* - The Schick test is an **in vivo** test used to determine susceptibility to **diphtheria** by injecting diphtheria toxin subcutaneously and observing for a localized inflammatory reaction. - A positive reaction (inflammation) indicates a lack of protective antitoxin antibodies. *Lepromin test* - The Lepromin test is an **in vivo** test used to assess the type of **leprosy** a patient has and to evaluate their cell-mediated immune response to *Mycobacterium leprae*. - It involves the intradermal injection of lepromin antigen and observing for a delayed hypersensitivity reaction. *Tuberculin test* - Also known as the **Mantoux test**, this is an **in vivo** test used to screen for exposure to **tuberculosis** by injecting purified protein derivative (PPD) intradermally. - A positive reaction indicates a **cell-mediated immune response** to *Mycobacterium tuberculosis*.

Q: Which microorganism is the most common cause of pyogenic osteomyelitis?

S. aureus. ***Staph aureus*** - **_Staphylococcus aureus_** is the most frequent cause of **pyogenic osteomyelitis** across all age groups and routes of infection. - Its ability to adhere to bone, form biofilms, and produce toxins contributes to its prevalence in bone infections. *Streptococcus spp.* - While various **_Streptococcus_** species can cause infections, they are less common causes of pyogenic osteomyelitis compared to **_Staphylococcus aureus_**. - **Group A _Streptococcus_** can cause severe invasive infections but rarely involves primary bone infection. *Corynebacterium spp.* - **_Corynebacterium_** species, particularly **_Corynebacterium striatum_**, are increasingly recognized as opportunistic pathogens, especially in immunocompromised individuals or those with foreign bodies. - However, they are not the most common cause of osteomyelitis in the general population. *Neisseria gonorrhoeae (gonococcus)* - **_Neisseria gonorrhoeae_** can cause **disseminated gonococcal infection (DGI)**, which may include joint involvement (**septic arthritis**). - While it can lead to bone pain and swelling, it primarily affects joints and is a less common cause of direct **pyogenic osteomyelitis** than **_S. aureus_**.

Question 1

In the context of diagnosing syphilis, which of the following is an example of a precipitation test?

Accepted Answer

Kahn test

Answer

Rose waaler test

Answer

Widal test

Answer

Latex agglutination

Question 2

Haptens are immunogenic when they covalently bind to which type of carrier?

Accepted Answer

Protein carrier

Answer

Lipid carrier

Answer

Polysaccharide carrier

Answer

None of the above carrier

Question 3

Which human IgG subclass has the highest serum concentration?

Accepted Answer

IgG1

Answer

IgG2

Answer

IgG3

Answer

IgG4

Question 4

Which of the following does not stimulate active immunity?

Accepted Answer

Transplacental antibody transfer in newborn

Answer

Clinical infection

Answer

Vaccination

Answer

Subclinical infection

Question 5

Which of the following is a specific feature of acquired immunity?

Accepted Answer

Immunological memory

Answer

Affected by genetic makeup

Answer

No antigen exposure

Answer

Immediate response

Question 6

Lattice phenomenon is seen in which of the following?

Accepted Answer

Precipitation test

Answer

Complement fixation test

Answer

None of the options

Answer

Neutralization reaction

Question 7

To which part of an antigen do monoclonal antibodies specifically bind?

Accepted Answer

Specific epitope on the antigen

Answer

None of the options

Answer

Both the epitope and the paratope

Answer

Part of the antibody that binds to the epitope

Question 8

What type of immunity is primarily associated with the administration of transfer factor?

Accepted Answer

Adoptive immunity

Answer

Natural active immunity

Answer

Artificial active immunity

Answer

Artificial passive immunity

Question 9

Which of the following tests is not classified as an in vivo test?

Accepted Answer

Elek's gel precipitation test

Answer

Schick test

Answer

Tuberculin test

Answer

Lepromin test

Question 10

Which microorganism is the most common cause of pyogenic osteomyelitis?

Accepted Answer

S. aureus

Answer

Streptococcus spp.

Answer

Corynebacterium spp.

Answer

Neisseria gonorrhoeae (gonococcus)

NEET-PG 2015 — Microbiology