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 641: 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 questionsWhat is the causative agent of Izumi fever?
Which 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?
NEET-PG 2015 - Microbiology NEET-PG Practice Questions and MCQs
Question 641: What is the causative agent of Izumi fever?
- A. Yersinia pseudotuberculosis (Correct Answer)
- B. Yersinia enterocolitica
- C. Pseudomonas aeruginosa
- D. Pasteurella multocida
Explanation: ***Yersinia pseudotuberculosis*** - Izumi fever (also called **Far East scarlet-like fever**) is caused by Yersinia pseudotuberculosis, particularly referring to outbreaks that occurred in Japan. - This infection presents with **fever, abdominal pain, and a scarlet fever-like rash**, often mimicking appendicitis due to mesenteric lymphadenitis. - Y. pseudotuberculosis is transmitted through **contaminated food and water**, and the Izumi fever variant is characterized by systemic manifestations including erythema and desquamation. *Yersinia enterocolitica* - While this is a closely related species that also causes **gastroenteritis and mesenteric adenitis**, it is NOT the causative agent of Izumi fever. - Y. enterocolitica typically presents with diarrhea, abdominal pain, and fever, but lacks the distinctive scarlet fever-like rash seen in Izumi fever. *Pseudomonas aeruginosa* - This bacterium is an **opportunistic pathogen** often associated with nosocomial infections, especially in immunocompromised individuals. - It causes **pneumonia**, urinary tract infections, and wound infections, but not Izumi fever. *Pasteurella multocida* - This bacterium is common in the **respiratory tracts of animals**, especially cats and dogs, and is a frequent cause of wound infections from animal bites or scratches. - It typically causes localized cellulitis, abscesses, and occasionally severe infections like meningitis or osteomyelitis, not Izumi fever.
Question 642: 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 643: 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 644: 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 645: 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 646: 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 647: 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 648: 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.
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 641: 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**.