River blindness is caused by?
What is required for precipitation in comparison to agglutination?
Which of the following statements about the VDRL test is LEAST accurate?
In the context of diagnosing syphilis, which of the following is an example of a precipitation test?
Haptens are immunogenic when they covalently bind to which type of carrier?
Which human IgG subclass has the highest serum concentration?
Which of the following does not stimulate active immunity?
Which of the following is a specific feature of acquired immunity?
Lattice phenomenon is seen in which of the following?
Which microorganism is the most common cause of pyogenic osteomyelitis?
NEET-PG 2015 - Microbiology NEET-PG Practice Questions and MCQs
Question 71: River blindness is caused by?
- A. Loa loa
- B. Ascaris
- C. B. malayi
- D. Onchocerca volvulus (Correct Answer)
Explanation: ***Onchocerca volvulus*** - **River blindness**, or **onchocerciasis**, is caused by the parasitic nematode *Onchocerca volvulus*. - This parasite is transmitted by the bite of infected **blackflies** (genus *Simulium*), which breed in fast-flowing rivers. *Loa loa* - *Loa loa* causes **Loiasis**, also known as African eye worm disease. - While it can manifest as an eye worm and cause itching and swelling, it does not typically lead to permanent blindness or the widespread skin lesions associated with river blindness. *Ascaris* - *Ascaris lumbricoides* causes **ascariasis**, an intestinal infection. - Symptoms are primarily gastrointestinal, such as abdominal pain, malnutrition, and, in severe cases, intestinal obstruction; it does not affect the eyes or cause blindness. *B. malayi* - *Brugia malayi* is one of the causes of **lymphatic filariasis**, also known as **elephantiasis**. - This disease primarily affects the lymphatic system, causing severe swelling in the limbs and genitals, but it does not cause blindness.
Question 72: What is required for precipitation in comparison to agglutination?
- A. Soluble antigen (Correct Answer)
- B. Increased temperature
- C. Specific cofactor
- D. Lower pH
Explanation: ***Soluble antigen*** - **Precipitation reactions** involve the interaction of antibodies with **soluble antigens** to form a detectable precipitate. - Unlike **agglutination**, which involves particulate antigens (e.g., cells), precipitation requires the antigen to be dissolved in a solution. *Increased temperature* - Most immunologic reactions, including precipitation and agglutination, are typically performed at **physiological temperatures** (e.g., 37°C) or room temperature. - An **increased temperature** is not a specific requirement that differentiates precipitation from agglutination. *Specific cofactor* - While some complex immunologic reactions might require **cofactors**, neither precipitation nor agglutination inherently requires a specific cofactor to occur. - The primary components are **antigen** and **antibody**. *Lower pH* - Both precipitation and agglutination reactions are sensitive to pH and typically occur within a **narrow pH range** close to neutral (e.g., pH 7.0-7.4). - A **lower pH** (acidic environment) could lead to antibody denaturation or non-specific aggregation, ultimately hindering the reaction rather than being a requirement.
Question 73: Which of the following statements about the VDRL test is LEAST accurate?
- A. VDRL is a treponemal-specific test with high specificity (Correct Answer)
- B. RPR is better than VDRL for monitoring drug therapy
- C. VDRL is a non-treponemal test and can give false positive results
- D. VDRL is a slide flocculation test for syphilis
Explanation: ***VDRL is a treponemal-specific test with high specificity*** - This statement is inaccurate because the **VDRL test** is a **non-treponemal** test, meaning it detects antibodies to cardiolipin, a lipid released from damaged host cells, rather than directly detecting antibodies to *Treponema pallidum*. - Non-treponemal tests like VDRL are known for their potential to produce **false-positive results** due to various conditions. *VDRL is a non-treponemal test and can give false positive results* - The **VDRL test** is indeed a **non-treponemal** test, detecting antibodies against cardiolipin, cholesterol, and lecithin. - Since it detects host-derived antibodies rather than specific *Treponema pallidum* antibodies, it is prone to **false-positive results** in conditions like autoimmune diseases, infections, and pregnancy. *RPR is better than VDRL for monitoring drug therapy* - Both **RPR (Rapid Plasma Reagin)** and VDRL are used to monitor response to therapy in syphilis, but **RPR is sometimes preferred** due to its ease of use (no need for a microscope), stability of reagents, and clearer macroscopic end-point. - The **titers of both VDRL and RPR typically decrease** after successful treatment, indicating a good response to therapy. *VDRL is a slide flocculation test for syphilis* - The **VDRL test** is a **flocculation test** where cardiolipin antigen mixed with a patient's serum (containing reagin antibodies) results in visible clumping or flocculation under a microscope. - It is used as a screening test for **syphilis**, caused by *Treponema pallidum*.
Question 74: In the context of diagnosing syphilis, which of the following is an example of a precipitation test?
- A. Rose waaler test
- B. Widal test
- C. Latex agglutination
- D. Kahn test (Correct Answer)
Explanation: ***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.
Question 75: Haptens are immunogenic when they covalently bind to which type of carrier?
- A. Lipid carrier
- B. Polysaccharide carrier
- C. Protein carrier (Correct Answer)
- D. None of the above carrier
Explanation: ***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.
Question 76: Which human IgG subclass has the highest serum concentration?
- A. IgG1 (Correct Answer)
- B. IgG2
- C. IgG3
- D. IgG4
Explanation: ***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.
Question 77: Which of the following does not stimulate active immunity?
- A. Clinical infection
- B. Vaccination
- C. Transplacental antibody transfer in newborn (Correct Answer)
- D. Subclinical infection
Explanation: ***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.
Question 78: Which of the following is a specific feature of acquired immunity?
- A. Immunological memory (Correct Answer)
- B. Affected by genetic makeup
- C. No antigen exposure
- D. Immediate response
Explanation: ***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.
Question 79: Lattice phenomenon is seen in which of the following?
- A. Complement fixation test
- B. Precipitation test (Correct Answer)
- C. None of the options
- D. Neutralization reaction
Explanation: ***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.
Question 80: Which microorganism is the most common cause of pyogenic osteomyelitis?
- A. S. aureus (Correct Answer)
- B. Streptococcus spp.
- C. Corynebacterium spp.
- D. Neisseria gonorrhoeae (gonococcus)
Explanation: ***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_**.