Internal Medicine
1 questionsWhat is the significance of the absence of Vi-antibody in a patient with typhoid fever?
NEET-PG 2015 - Internal Medicine NEET-PG Practice Questions and MCQs
Question 721: What is the significance of the absence of Vi-antibody in a patient with typhoid fever?
- A. Indicates a poor prognosis
- B. Indicates a favorable prognosis (Correct Answer)
- C. No impact on prognosis
- D. Suggests a negative response to treatment
Explanation: ***Indicates a favorable prognosis*** - The **Vi (Virulence) antigen** is a **polysaccharide capsule** that helps *Salmonella typhi* evade the immune system and is associated with **virulence** and **carrier state development**. - **Absence of Vi-antibody** indicates infection with a **less virulent strain**, successful **immune clearance**, and **lower likelihood** of developing a chronic carrier state. *Indicates a poor prognosis* - The **absence of Vi-antibody** is actually associated with **better outcomes**, not worse prognosis. - **Poor prognosis** in typhoid fever is typically related to complications like **intestinal perforation** or **septic shock**, not Vi-antibody status [1]. *No impact on prognosis* - **Vi-antibody status** is a **recognized prognostic marker** in typhoid fever and does have clinical significance. - The **presence of Vi-antibodies** may indicate **persistent infection** or **carrier state development**, making it a relevant prognostic indicator. *Suggests a negative response to treatment* - **Absence of Vi-antibody** typically indicates **successful treatment response** and **effective clearance** of the organism. - **Negative treatment response** would be evidenced by **persistent fever**, **positive cultures**, or **clinical deterioration** despite appropriate antibiotic therapy.
Microbiology
8 questionsWhich of the following statements about the Widal test is true?
What is the clinical significance of the Vi antigen in Salmonella typhi?
Which of the following is a non-motile bacterium?
Which of the following is non-motile:
Phagocytosis of mycobacterium tuberculosis by macrophages is mainly mediated by:
Which test is used to differentiate staphylococci from micrococci?
Which of the following is NOT true about Corynebacterium hofmannii?
Which of the following statements about Corynebacterium diphtheriae is true?
NEET-PG 2015 - Microbiology NEET-PG Practice Questions and MCQs
Question 721: Which of the following statements about the Widal test is true?
- A. The H-antigen is the most immunogenic.
- B. Felix tubes are not used in the Widal test.
- C. Anti-O antibody persists longer than anti-H antibody.
- D. The O antigen used in the Widal test is from S. typhi. (Correct Answer)
Explanation: ***Correct: The O antigen used in the Widal test is from S. typhi.*** - The Widal test uses **O (somatic) antigens from S. Typhi** to detect anti-O antibodies - It also uses **H (flagellar) antigens from S. Typhi** to detect anti-H antibodies - Additionally, antigens from **S. Paratyphi A and B** are included for comprehensive detection of enteric fever - The statement is correct that O antigen from S. typhi is used (along with antigens from other organisms) *Incorrect: The H-antigen is the most immunogenic.* - The **O antigen** is generally considered more immunogenic than the H antigen in enteric fever - Anti-O antibodies appear earlier and are more specific for acute infection - However, O antibodies disappear faster after recovery *Incorrect: Felix tubes are not used in the Widal test.* - **Dreyer's tubes** (also known as Felix tubes) are traditionally used in the Widal test - These special tubes allow for quantitative antibody titration - They enable observation of agglutination patterns at different serum dilutions *Incorrect: Anti-O antibody persists longer than anti-H antibody.* - This is **backwards** - Anti-H antibodies actually persist longer (can last for years) - **Anti-O antibodies** appear later and disappear relatively quickly after infection resolves - Anti-O antibodies are more indicative of acute/recent infection - Anti-H antibodies are less specific due to their prolonged persistence and possible cross-reactions
Question 722: What is the clinical significance of the Vi antigen in Salmonella typhi?
- A. Stimulates an immune response
- B. Indicates carrier status in individuals (Correct Answer)
- C. Not primarily used in Widal test
- D. Used for diagnosing typhoid fever
Explanation: ***Indicates carrier status in individuals*** - The **Vi (Virulence) antigen** is a **capsular polysaccharide** found on *Salmonella typhi* that helps the bacterium evade immune responses - The presence of persistent **anti-Vi antibodies** is the **hallmark of chronic typhoid carriers**, particularly those harboring bacteria in the **gallbladder** - Vi antibody testing is specifically used for **carrier screening** and identification, as carriers maintain high anti-Vi titers even without active symptoms - This is the **primary clinical significance** of the Vi antigen in diagnostic microbiology *Used for diagnosing typhoid fever* - This is **incorrect** - the Vi antigen is NOT used for diagnosing acute typhoid fever - The standard **Widal test** detects antibodies against **O (somatic)** and **H (flagellar)** antigens, NOT Vi antigen - Acute diagnosis relies on **blood culture** and detection of O and H antibodies, not Vi antibodies - Vi antibodies appear later in infection and persist longer, making them markers of **chronic carriage** rather than acute disease *Stimulates an immune response* - While true that Vi antigen stimulates antibody production, this is not its **clinical significance** - All bacterial antigens stimulate immune responses - this doesn't distinguish Vi antigen's specific clinical utility - The key clinical value lies in its use for **carrier detection**, not merely immunogenicity *Not primarily used in Widal test* - This is a **true statement** but not the answer to what the clinical significance IS - The Widal test uses O and H antigens for acute diagnosis - While accurate, this option describes what Vi antigen is NOT used for, rather than its actual clinical significance as a **carrier marker**
Question 723: Which of the following is a non-motile bacterium?
- A. Clostridium perfringens (Correct Answer)
- B. Vibrio
- C. Legionella
- D. Clostridium septicum
Explanation: ***Clostridium perfringens*** - *Clostridium perfringens* is unique among the *Clostridium* species for being **non-motile**, lacking flagella. - This immotility distinguishes it from other closely related bacteria and is an important characteristic in its identification. *Vibrio* - *Vibrio* species are **highly motile**, possessing a single **polar flagellum** that enables rapid movement in liquid environments. - Their motility is crucial for their survival and pathogenesis, particularly in aquatic habitats and the human intestine. *Legionella* - *Legionella* species, including *Legionella pneumophila*, are **motile** by means of one or more **polar flagella**. - Their motility is important for disseminating within water systems and for infecting macrophages. *Clostridium septicum* - *Clostridium septicum* is a **motile** bacterium, possessing **peritrichous flagella** that allow it to move through tissues. - Its motility contributes to its ability to spread rapidly in infected hosts, often causing severe gas gangrene.
Question 724: Which of the following is non-motile:
- A. Pseudomonas aeruginosa
- B. Burkholderia mallei (Correct Answer)
- C. Burkholderia pseudomallei
- D. None of the options
Explanation: ***Burkholderia mallei*** - This bacterium is notably **non-motile**, lacking flagella, which is a key characteristic differentiating it from other members of its genus. - It is a **facultative intracellular pathogen** capable of surviving within host cells, primarily causing **glanders** in equids and occasional human infections. - Its immobility is a significant feature in its identification and pathogenesis. *Pseudomonas aeruginosa* - This bacterium is highly **motile** due to the presence of **polar flagella**. - Its motility contributes to its ability to colonize and invade host tissues, common in opportunistic infections. *Burkholderia pseudomallei* - This species is known to be **motile** by means of flagella, which aids its survival and dissemination in diverse environments and within a host. - It is the causative agent of **melioidosis**, a severe infectious disease. *None of the options* - This option is incorrect because **Burkholderia mallei** is indeed non-motile, making it a correct choice among the provided options. - The other specified bacteria, *Pseudomonas aeruginosa* and *Burkholderia pseudomallei*, are motile.
Question 725: Phagocytosis of mycobacterium tuberculosis by macrophages is mainly mediated by:
- A. Interleukin 6
- B. Interleukin 3
- C. Interleukin 12
- D. Interferon Gamma (Correct Answer)
Explanation: ***Interferon Gamma*** - **Interferon gamma (IFN-γ)** is the most critical cytokine for **macrophage activation** in tuberculosis, enabling effective phagocytosis and intracellular killing of **Mycobacterium tuberculosis**. - IFN-γ (produced by **Th1 cells** and **NK cells**) primes macrophages by: - Enhancing **phagosome-lysosome fusion** - Increasing expression of **Fc receptors** and **complement receptors** for better opsonization - Stimulating production of **reactive oxygen species (ROS)** and **nitric oxide (NO)** - Upregulating **MHC class II** for improved antigen presentation - Without IFN-γ, macrophages cannot effectively control intracellular mycobacterial growth (as seen in **IFN-γ or IL-12 receptor deficiencies** leading to disseminated mycobacterial infections). *Interleukin 6* - **IL-6** is a pro-inflammatory cytokine involved in **acute-phase responses**, fever induction, and B-cell differentiation. - While it contributes to systemic inflammatory responses in TB, it does not directly activate macrophages for mycobacterial phagocytosis and killing. *Interleukin 3* - **IL-3** is a **hematopoietic growth factor** that promotes proliferation and differentiation of myeloid and lymphoid progenitor cells in bone marrow. - It plays no direct role in the effector functions of mature macrophages against *M. tuberculosis*. *Interleukin 12* - **IL-12** (produced by macrophages and dendritic cells) is essential for initiating **Th1 immunity** by promoting differentiation of naive CD4+ T cells into **Th1 cells** that produce IFN-γ. - IL-12 acts **upstream** of IFN-γ in the immune cascade but does not directly mediate macrophage phagocytic function. - The **IL-12/IFN-γ axis** is critical for TB immunity, but IFN-γ is the direct macrophage activator.
Question 726: Which test is used to differentiate staphylococci from micrococci?
- A. Coagulase test
- B. Oxidation-Fermentation (O/F) test (Correct Answer)
- C. Novobiocin sensitivity
- D. Catalase test
Explanation: ***Oxidation-Fermentation (O/F) test*** - The **oxidation-fermentation (O/F) test** is used to determine whether an organism metabolizes carbohydrates strictly oxidatively, fermentatively, or both. - **Staphylococci** are facultative anaerobes that ferment glucose, while **micrococci** are strict aerobes that metabolize glucose oxidatively, making this test key for differentiation. *Catalase test* - The catalase test differentiates **catalase-positive** organisms (like both Staphylococci and Micrococci) from **catalase-negative** organisms (like Streptococci). - Since both Staphylococci and Micrococci are catalase-positive, this test cannot differentiate between them. *Coagulase test* - The coagulase test differentiates **Staphylococcus aureus** (coagulase-positive) from other **coagulase-negative Staphylococci (CoNS)**. - This test is specific for distinguishing within the Staphylococcus genus and does not apply to Micrococci. *Novobiocin sensitivity* - Novobiocin sensitivity is primarily used to differentiate **Staphylococcus saprophyticus** (resistant) from other **coagulase-negative Staphylococci** (sensitive). - It is not used to distinguish between the genera Staphylococci and Micrococci.
Question 727: Which of the following is NOT true about Corynebacterium hofmannii?
- A. Commonly found in the normal flora of the throat
- B. A diphtheroid
- C. Non-pathogenic saprophyte
- D. Toxigenic (Correct Answer)
Explanation: ***Toxigenic*** - *Corynebacterium hofmannii* is a **non-toxigenic** species and does not produce **diphtheria toxin**, unlike *C. diphtheriae*. - Its clinical significance primarily relates to its potential role in opportunistic infections, not toxin-mediated diseases. - This is the **correct answer** as C. hofmannii being toxigenic is NOT true. *A diphtheroid* - **Diphtheroid** refers to gram-positive, rod-shaped bacteria morphologically similar to *Corynebacterium diphtheriae*. - *C. hofmannii* fits this description due to its characteristic morphology and belongs to the Corynebacterium genus. - This statement is TRUE. *Non-pathogenic saprophyte* - *C. hofmannii* is commonly found as a **commensal organism** on human skin and mucous membranes as part of normal flora. - While generally non-pathogenic, it can cause opportunistic infections in immunocompromised individuals. - This statement is TRUE. *Commonly found in the normal flora of the throat* - *C. hofmannii* is indeed found as part of the **normal respiratory tract flora**, including the throat and upper respiratory passages. - It is a common colonizer and generally harmless commensal. - This statement is TRUE.
Question 728: Which of the following statements about Corynebacterium diphtheriae is true?
- A. All strains produce toxin
- B. Toxin production is dependent on iron concentration (Correct Answer)
- C. The toxin is heat stable
- D. It inhibits cAMP
Explanation: ***Toxin production is dependent on iron concentration*** - The production of **diphtheria toxin** by *Corynebacterium diphtheriae* is directly regulated by the iron concentration in the environment. - When **iron levels are low**, the diphtheria toxin repressor (DTxR) is inactivated, leading to increased toxin production. *All strains produce toxin* - Not all strains of *Corynebacterium diphtheriae* produce the diphtheria toxin; only those strains that are **lysogenized by a bacteriophage carrying the tox gene** are toxigenic. - Non-toxigenic strains can cause other infections but do not produce the classic diphtheria disease. *The toxin is heat stable* - The **diphtheria toxin** is a **heat-labile** protein, meaning its activity can be destroyed by heat. - Heating diphtheria toxin to 60°C for 30 minutes can inactivate its pathogenic effects. *It inhibits cAMP* - The diphtheria toxin does not inhibit **cAMP**; instead, it acts by **ADP-ribosylating and inactivating elongation factor-2 (EF-2)**, thereby inhibiting protein synthesis in eukaryotic cells. - Inhibition of EF-2 ultimately leads to cell death.
Pharmacology
1 questionsWhich of the following is not true about the Vi polysaccharide vaccine for typhoid?
NEET-PG 2015 - Pharmacology NEET-PG Practice Questions and MCQs
Question 721: Which of the following is not true about the Vi polysaccharide vaccine for typhoid?
- A. Given intramuscularly
- B. Given at birth (Correct Answer)
- C. Revaccination at 3 years
- D. Single dose is given
Explanation: ***Given at birth*** - The **typhoid Vi polysaccharide vaccine is not administered at birth**. It is recommended for individuals **2 years of age**. - Vaccines given at birth protect against diseases with significant **neonatal risk**, such as Hepatitis B and BCG (tuberculosis). - This is the **FALSE** statement, making it the correct answer to this "not true" question. *Single dose is given* - The Vi polysaccharide vaccine is administered as a **single 0.5 mL dose**. - This single dose provides protection against *Salmonella typhi* for approximately 3 years. - This statement is **TRUE**. *Revaccination at 3 years* - For ongoing protection, **revaccination is recommended every 3 years** for individuals at continued risk of typhoid exposure. - The booster dose maintains adequate protective antibody levels. - This statement is **TRUE**. *Given intramuscularly* - The Vi polysaccharide vaccine is administered via the **intramuscular (IM) route**, typically in the deltoid muscle. - This is the standard recommended route of administration. - This statement is **TRUE**.