Which of the following substances is toxic to parasites?
Smallpox belongs to which genus of poxviruses?
When is the prozone phenomenon seen?
A patient with sore throat has a positive Paul Bunnell test, indicating infectious mononucleosis. The causative organism is?
Which of the following statements is true regarding T cell independent antigens?
Acute Infective Endocarditis with abscess formation is most commonly associated with
Most common bacterial cause of acute parotitis -
An 18-year-old girl presents with watery diarrhea. Most likely causative agent -
Ehrlichia chaffeensis is the causative agent of -
Hanging drop method is used for:
NEET-PG 2012 - Microbiology NEET-PG Practice Questions and MCQs
Question 61: Which of the following substances is toxic to parasites?
- A. Peroxidase (Correct Answer)
- B. Interferon-alpha
- C. IL-2 (Interleukin-2)
- D. IL-6 (Interleukin-6)
Explanation: ***Peroxidase*** - **Peroxidase** enzymes, especially those produced by **eosinophils**, generate toxic oxygen metabolites and hypohalous acids that are highly effective at damaging and killing parasites. - This enzyme plays a crucial role in the host's defense against larger parasites, such as **helminths (worms)**. *Interferon-alpha* - **Interferon-alpha** is an important cytokine primarily known for its **antiviral effects** and its role in activating natural killer (NK) cells. - While it modulates immune responses, it does not directly act as a toxic substance to parasites. *IL-2 (Interleukin-2)* - **IL-2** is a growth factor that primarily promotes the **proliferation and differentiation of T cells**, enhancing adaptive immune responses. - It does not directly kill parasites but rather supports the immune cells involved in parasite clearance. *IL-6 (Interleukin-6)* - **IL-6** is a pleiotropic cytokine involved in **inflammation, acute phase responses**, and the differentiation of B cells and T cells. - While it contributes to overall immune regulation, it lacks direct parasiticidal activity.
Question 62: Smallpox belongs to which genus of poxviruses?
- A. Leporipoxvirus
- B. Orthopoxvirus (Correct Answer)
- C. Capripoxvirus
- D. Parapoxvirus
Explanation: ***Orthopoxvirus*** - **Smallpox** (caused by the **variola virus**) is a classic member of the Orthopoxvirus genus. - This genus includes other human pathogens like **monkeypox** and vaccinia virus (used in the smallpox vaccine). *Parapoxvirus* - This genus includes viruses like **Orf virus** (causing contagious pustular dermatitis in sheep and goats) and pseudocowpox virus. - These viruses typically cause milder, localized lesions and are morphologically distinct from orthopoxviruses. *Capripoxvirus* - This genus includes viruses primarily affecting livestock, such as **lumpy skin disease virus**, sheep pox virus, and goat pox virus. - They cause systemic infections and skin lesions in their respective animal hosts and are not associated with human disease like smallpox. *Leporipox virus* - This genus includes viruses that primarily infect rabbits and hares, such as **myxoma virus** and fibroma virus. - These viruses typically cause tumors or severe systemic disease in their rabbit hosts and are not known to infect humans.
Question 63: When is the prozone phenomenon seen?
- A. Same concentration of antibody and antigen
- B. Hyperimmune reaction
- C. In antigen excess to antibody
- D. Antibody excess to antigen (Correct Answer)
Explanation: ***Antibody excess to antigen*** - The **prozone phenomenon** occurs when there is a significant **excess of antibodies** relative to the antigen, leading to inhibition of lattice formation. - In this state, too many antibodies bind to individual antigen sites, preventing cross-linking and thus inhibiting visible **agglutination** or **precipitation**. *Same concentration of antibody and antigen* - This scenario typically represents the **zone of equivalence**, where optimal lattice formation and visible reaction (agglutination or precipitation) occur. - It is where the concentrations of antibody and antigen are balanced, leading to maximum complex formation. *In antigen excess to antibody* - This situation is known as the **postzone phenomenon**, where an excess of antigen prevents the formation of stable antibody-antigen complexes. - The antigen saturates the limited antibody sites, resulting in no or minimal visible reaction. *Hyperimmune reaction* - A hyperimmune reaction refers to an **exaggerated immune response**, often resulting from repeated exposure to an antigen. - While it involves high antibody levels, it is a clinical state rather than a specific phenomenon describing antibody-antigen ratios in *in vitro* tests.
Question 64: A patient with sore throat has a positive Paul Bunnell test, indicating infectious mononucleosis. The causative organism is?
- A. EBV (Correct Answer)
- B. Adenovirus
- C. CMV
- D. HSV (Herpes Simplex Virus)
Explanation: ***Correct: EBV*** - The **Paul-Bunnell test** (monospot test) detects **heterophile antibodies**, which are characteristic of acute **Epstein-Barr virus (EBV)** infection. - **EBV** is the primary causative agent of **infectious mononucleosis**, commonly known as "mono." *Incorrect: Adenovirus* - **Adenoviruses** can cause various infections, including **pharyngitis** and **conjunctivitis**, but are not associated with a positive **Paul-Bunnell test** or heterophile antibodies. - While it can cause sore throat, the presence of a **positive Paul-Bunnell test** differentiates it from EBV. *Incorrect: CMV* - **Cytomegalovirus (CMV)** can cause a mononucleosis-like syndrome, but it typically results in a **negative Paul-Bunnell test** (i.e., it is heterophile antibody-negative). - CMV mononucleosis is often seen in individuals who are **immunocompromised** or in infants as a congenital infection. *Incorrect: HSV (Herpes Simplex Virus)* - **Herpes simplex virus (HSV)** causes infections such as **oral herpes (cold sores)** and **genital herpes**, and in some cases, **pharyngitis**. - HSV infection is not associated with a positive **Paul-Bunnell test** or the production of heterophile antibodies.
Question 65: Which of the following statements is true regarding T cell independent antigens?
- A. They primarily activate T-cells.
- B. They primarily activate B-cells. (Correct Answer)
- C. They primarily activate macrophages.
- D. They primarily activate CD8+ T cells.
Explanation: ***Correct: They primarily activate B-cells*** - T-cell independent antigens are typically **polysaccharides** (TI-2) or **lipopolysaccharides** (TI-1) with repeating epitopes that can directly cross-link B cell receptors (BCRs) - This direct binding and cross-linking provide a strong enough signal to activate B cells and induce **antibody production** (mainly IgM) without the need for T cell help - They induce a rapid but limited immune response with minimal memory formation *Incorrect: They primarily activate T-cells* - T-cell independent antigens do not require processing and presentation by **MHC molecules**, which is essential for T cell activation - T cells recognize processed peptides presented by MHC, a mechanism not utilized by T-cell independent antigens - By definition, these antigens activate B cells **without** T cell involvement *Incorrect: They primarily activate macrophages* - While macrophages are antigen-presenting cells, their primary role in adaptive immunity is to process and present antigens to T cells - Macrophages are involved in **phagocytosis** and antigen processing, but are not the primary target cells for T-independent antigens - The key feature of TI antigens is direct B cell activation, not macrophage activation *Incorrect: They primarily activate CD8+ T cells* - **CD8+ T cells** are activated by processed antigens presented on **MHC class I molecules**, typically derived from intracellular pathogens - T-cell independent antigens do not utilize this pathway and are primarily involved in **humoral immunity** through direct B cell activation - TI antigens cannot activate CD8+ T cells as they bypass the T cell-dependent pathway entirely
Question 66: Acute Infective Endocarditis with abscess formation is most commonly associated with
- A. Listeria
- B. Staphylococcus (Correct Answer)
- C. Streptococcus
- D. Enterococcus
Explanation: ***Staphylococcus*** - **_Staphylococcus aureus_** is the most common cause of **acute infective endocarditis (AIE)** and is particularly virulent, leading to rapid valve destruction and **abscess formation**. - Its ability to adhere to damaged endothelium and produce various toxins contributes to its high pathogenicity and propensity for complicated infections. *Listeria* - **_Listeria monocytogenes_** is a gram-positive rod known to cause meningitis and gastrointestinal infections, especially in immunocompromised individuals. - While it can rarely cause endocarditis, it is not typically associated with the majority of AIE cases or abscess formation. *Streptococcus* - **_Streptococcus_ species**, particularly **_Viridans streptococci_**, are commonly associated with **subacute infective endocarditis (SIE)** on previously damaged valves. - They generally cause a more indolent course and are less frequently linked to rapid valve destruction or abscess formation compared to _Staphylococcus aureus_. *Enterococcus* - **_Enterococcus_ species** are a common cause of endocarditis, especially in older patients, those with healthcare-associated infections, or urinary tract procedures. - While they can cause serious infections, **_Staphylococcus aureus_** remains the predominant pathogen for acute infective endocarditis with abscess formation.
Question 67: Most common bacterial cause of acute parotitis -
- A. Staphylococcus Aureus (Correct Answer)
- B. Klebsiella
- C. Streptococcus Viridans
- D. Streptococcus Pneumoniae
Explanation: ***Staphylococcus Aureus*** - **_Staphylococcus aureus_** is the most frequent bacterial pathogen isolated in cases of **acute bacterial parotitis**. [2] - It often causes ascending infection from the oral cavity, leading to inflammation and suppuration of the parotid gland. [1] *Streptococcus Pneumonia* - While **_Streptococcus pneumoniae_** can cause various infections, it is not the primary cause of acute bacterial parotitis. - Its infections more commonly manifest as **pneumonia**, otitis media, or meningitis. *Klebsiella* - **_Klebsiella_** species are typically associated with **nosocomial infections**, particularly urinary tract infections and pneumonia. - They are a relatively uncommon cause of acute parotitis compared to _S. aureus_. *Streptococcus Viridans* - **_Streptococcus viridans_** group bacteria are common commensal organisms of the oral cavity and are often implicated in **dental caries** and **endocarditis**. - They are not a usual cause of acute bacterial parotitis.
Question 68: An 18-year-old girl presents with watery diarrhea. Most likely causative agent -
- A. Rotavirus
- B. V. cholerae (Correct Answer)
- C. Salmonella
- D. Shigella
Explanation: ***V. cholerae*** - *Vibrio cholerae* is a classic cause of **acute, severe watery diarrhea** that can lead to rapid dehydration. - While other agents can cause watery diarrhea, *V. cholerae* is primarily associated with large-scale outbreaks of this symptom. *Rota virus* - While rotavirus causes **watery diarrhea**, it primarily affects **infants and young children** and is less common as the most likely cause in an 18-year-old in many settings due to widespread vaccination programs. - The diarrhea, though watery, is often accompanied by **fever and vomiting**. *Salmonella* - *Salmonella* typically causes **inflammatory diarrhea** (dysentery-like symptoms with blood/mucus in stool) or **food poisoning**, with diarrhea that may be watery but is often not as profuse or severe as cholera. - It is more commonly associated with **fever and abdominal cramps**. *Shigella* - *Shigella* causes **bacillary dysentery**, characterized by **bloody, mucoid stools**, abdominal cramps, and fever. - It is not typically associated with solely profuse watery diarrhea.
Question 69: Ehrlichia chaffeensis is the causative agent of -
- A. HME (Correct Answer)
- B. Glandular fever
- C. HGE
- D. None of the options
Explanation: ***HME (Human Monocytic Ehrlichiosis)*** - **Ehrlichia chaffeensis** is the primary causative agent of **Human Monocytic Ehrlichiosis**, a tick-borne illness. - This bacterium primarily infects **monocytes** and macrophages, leading to characteristic intracellular inclusions called **morulae**. *Glandular fever* - Glandular fever, also known as **infectious mononucleosis**, is predominantly caused by the **Epstein-Barr virus (EBV)**. - It is characterized by fever, sore throat, lymphadenopathy, and fatigue, and is not caused by bacteria. *HGE (Human Granulocytic Ehrlichiosis)* - **Human Granulocytic Ehrlichiosis (HGE)** is caused by **Anaplasma phagocytophilum**, not *Ehrlichia chaffeensis*. - HGE primarily targets **neutrophils** (granulocytes), differentiating it from HME which targets monocytes. *None of the options* - This option is incorrect because *Ehrlichia chaffeensis* is indeed the causative agent of HME, as described above.
Question 70: Hanging drop method is used for:
- A. Toxoplasma
- B. Cryptosporidium
- C. Trichomonas (Correct Answer)
- D. Plasmodium
Explanation: ***Trichomonas*** - The **hanging drop method** is a highly effective technique for visualizing the characteristic **motility** of *Trichomonas vaginalis*. - This method allows for the observation of living, unstained organisms directly from clinical samples, making it valuable for rapid diagnosis. *Toxoplasma* - **Toxoplasma gondii** is an intracellular parasite best identified through serological tests for **antibodies** or molecular diagnostics like **PCR**. - It does not exhibit characteristic motility in a hanging drop preparation that would aid in its direct identification. *Cryptosporidium* - **Cryptosporidium** species are typically identified by detecting **oocysts** in stool samples, often using **acid-fast staining** or **immunofluorescence assays**. - Their small size and lack of distinctive motility under a hanging drop method make this technique unsuitable for their diagnosis. *Plasmodium* - **Plasmodium** species, the causative agents of malaria, are diagnosed by visualizing **parasites within red blood cells** on **Giemsa-stained blood smears**. - The hanging drop method would not effectively identify these intracellular parasites for malaria diagnosis.