NEET-PG 2013 Practice Questions

Q: Vaccines are available against which types of meningococcus?

Type A, B, C, W, and Y. ***Type A, B, C, W, and Y*** - Vaccines are currently available against **all five major meningococcal serogroups**: A, B, C, W-135, and Y. - **Meningococcal conjugate vaccines (MenACWY)** provide protection against serogroups A, C, W-135, and Y, and are widely used globally. - **Meningococcal B vaccines (MenB)** such as Bexsero and Trumenba specifically target serogroup B, which is a leading cause of meningococcal disease in developed countries. - Combined, these vaccines provide comprehensive coverage against the most epidemiologically important meningococcal serogroups worldwide. *Type A* - While vaccines against **meningococcus type A** do exist (as part of conjugate vaccines), this option is incomplete as it excludes the other important serogroups (B, C, W, Y) for which vaccines are also available. *Type B* - **Type B vaccines** are available and important, particularly in developed countries where serogroup B causes significant disease burden. - However, this option alone is insufficient because vaccines also effectively target other serogroups (A, C, W, Y). *Type A, B, and C* - This option is incomplete because it omits **serogroups W and Y**, for which conjugate vaccines (MenACWY) are readily available and widely used. - The question asks which types vaccines are *available* against, not which are most common, making this an incorrect answer.

Q: Waterhouse-Friderichsen syndrome is seen in:

Neisseria meningitidis. ***Neisseria meningitidis*** - **Waterhouse-Friderichsen syndrome** is a severe complication of **meningococcal sepsis**, predominantly caused by *Neisseria meningitidis* [1]. - It is characterized by **adrenal gland hemorrhage**, leading to acute adrenal insufficiency, hemorrhagic skin rash, and shock [1]. *Pseudomonas* - While *Pseudomonas aeruginosa* can cause severe infections, including sepsis, it is **not typically associated** with Waterhouse-Friderichsen syndrome. - *Pseudomonas* infections often lead to **ecthyma gangrenosum** in immunocompromised patients, a different dermatological manifestation. *Yersinia* - *Yersinia* species can cause various infections, such as **yersiniosis** (gastroenteritis) and **plague** (*Yersinia pestis*). - These infections do not commonly present with the distinct features of **adrenal hemorrhage** and **fulminant sepsis** seen in Waterhouse-Friderichsen syndrome. *Pneumococci* - *Streptococcus pneumoniae* (**pneumococci**) is a common cause of **meningitis** and **sepsis**, especially in children and the elderly. - Although it can lead to severe bloodstream infections, it is **rarely specifically linked** to the adrenal hemorrhage syndrome known as Waterhouse-Friderichsen syndrome.

Q: Which of the following statements about Corynebacterium diphtheriae is NOT true?

Toxin mediated by chromosomal gene. ***Toxin mediated by chromosomal gene*** - The **diphtheria toxin** is encoded by the **tox gene**, which is a lysogenic bacteriophage (cornyphage) gene, not a chromosomal gene. - This **bacteriophage** integrates into the bacterial chromosome, making toxigenic *C. diphtheriae* strains lysogenized. *Has metachromatic granules* - *Corynebacterium diphtheriae* is known for possessing **metachromatic granules** (also called Babes-Ernst bodies), which are inclusions that stain differently from the rest of the cell. - These granules are composed of **polyphosphate reserves** and are important for identification. *Does not invade deeper tissues* - *Corynebacterium diphtheriae* remains **localized** to the mucosal surface of the upper respiratory tract or skin, forming a **pseudomembrane**. - Its pathogenicity is primarily due to the **exotoxin** it produces, which then disseminates systemically. *Toxigenicity demonstrated by elek's test* - The **Elek test** is a standard laboratory assay used to determine the **toxigenicity** of *Corynebacterium diphtheriae* strains by detecting the production of diphtheria toxin. - It works by identifying the **immunoprecipitation lines** formed between antitoxin and toxin in an agar medium.

Q: Pneumococcal vaccine is prepared from ?

Capsular polysaccharide. ***Capsular polysaccharide*** - The **polysaccharide capsule** of *Streptococcus pneumoniae* is the primary virulence factor, protecting the bacteria from phagocytosis. - Vaccines, such as **PCV13** (pneumococcal conjugate vaccine) and **PPSV23** (pneumococcal polysaccharide vaccine), are designed targeting these capsular polysaccharides to elicit a protective immune response. *Cell surface antigen* - While bacteria possess various **cell surface antigens**, not all are immunogenic or provide protective immunity as effectively as the capsular polysaccharides for *S. pneumoniae*. - For pneumococcus, the **capsule** is the most critical surface component for vaccine development due to its role in virulence and serotype specificity. *From exotoxin* - *S. pneumoniae* primarily causes disease through its **polysaccharide capsule** and other bacterial components, not through the production of an **exotoxin** that would be targeted by a vaccine. - Vaccines developed from exotoxins (e.g., diphtheria or tetanus toxoids) target specific toxins, which is not the mechanism for pneumococcal vaccines. *From M protein* - **M protein** is a major virulence factor for *Streptococcus pyogenes* (Group A Strep), not *Streptococcus pneumoniae*. - Vaccines targeting M protein are associated with **Group A Streptococcus** infections, for protection against diseases like rheumatic fever.

Q: What component is included in the vaccine against N-meningitidis?

Capsular polysaccharide (polysaccharide vaccine). ***Capsular polysaccharide (polysaccharide vaccine)*** - *Neisseria meningitidis* vaccines commonly include **capsular polysaccharides** from different serogroups (A, C, Y, W-135) to elicit a protective immune response. - These polysaccharides act as antigens, stimulating the production of **antibodies** that can neutralize the bacteria. - **Conjugate vaccines** combine polysaccharides with carrier proteins to improve immunogenicity, especially in infants and young children. *Killed whole-cell vaccine* - **Killed whole-cell vaccines** are not used for *N. meningitidis* due to potential reactogenicity and the availability of more effective targeted antigens. - **Polysaccharide and conjugate vaccines** are the established formulations for meningococcal disease prevention. *Outer membrane protein (OMP)* - **Outer membrane proteins (OMPs)** are specifically used in **serogroup B vaccines** (e.g., Bexsero, Trumenba) due to the poor immunogenicity of the serogroup B polysaccharide capsule. - However, for serogroups A, C, Y, and W-135, **capsular polysaccharide** remains the primary vaccine component. *Live attenuated vaccine* - **Live attenuated vaccines** are not used for *N. meningitidis* as they pose risks of reversion to virulence and are unnecessary given the effectiveness of polysaccharide-based vaccines. - Meningococcal vaccines rely on **subunit approaches** (polysaccharides, conjugates, OMPs) rather than live organisms.

Q: Which organism is responsible for producing Draughtsman (Concentric Rings) on culture?

Bacillus anthracis. ***Bacillus anthracis*** - *Bacillus anthracis* is the organism responsible for producing the characteristic **"Draughtsman" or "Concentric Rings"** pattern on culture media - On blood agar, colonies show a **"Medusa head"** appearance with **concentric rings** and **comma-shaped projections** radiating outward from the center - This distinctive morphology results from chains of bacilli growing in parallel alignment, creating the characteristic pattern - The colonies are typically **non-hemolytic, grey-white, and have irregular edges** *H. ducreyi* - *Haemophilus ducreyi* causes **chancroid** and is difficult to culture - Colonies appear as **small, grey-yellow, translucent** with a **cohesive ("school of fish")** appearance when pushed across the agar - Does not produce concentric rings *B. pertussis* - *Bordetella pertussis* grows on **Bordet-Gengou agar** or **Regan-Lowe medium** - Colonies have a characteristic **"mercury droplet"** or **"bisected pearl"** appearance due to their smooth, shiny, convex morphology - This is completely different from the Draughtsman pattern *Pneumococci* - *Streptococcus pneumoniae* produces **alpha-hemolytic colonies** on blood agar - Colonies are **small, dome-shaped, mucoid** with a **central umbilication** (draughtsman or checker-piece appearance refers to the depression, not concentric rings) - The "draughtsman" term when applied to pneumococci refers to the flattened checker-piece shape, not the concentric ring pattern of *B. anthracis*

Q: What is the primary use of the Hybridoma technique?

Monoclonal antibodies. ***Monoclonal antibodies*** - The **hybridoma technique** is primarily used to produce **monoclonal antibodies (MAbs)**, which are highly specific antibodies derived from a single B-cell clone. - These antibodies recognize a **single epitope** on an antigen, providing exceptional specificity and uniformity. - The technique involves **fusing a B-lymphocyte** (antibody-producing cell) with a **myeloma cell** (immortal cancer cell) to create a hybridoma that continuously produces identical antibodies. - This is the **gold standard** for producing large quantities of identical, highly specific antibodies for diagnostic and therapeutic use. *Specific antibodies* - While monoclonal antibodies are indeed specific, this term is **too vague** and could refer to any antibody with specificity, including polyclonal antibodies. - **Polyclonal antibodies** are also specific but are produced through conventional immunization, not the hybridoma technique. - The defining characteristic of the hybridoma technique is that it produces **monoclonal** (single clone) antibodies, not just "specific" ones. *Antigen* - An **antigen** is a molecule that elicits an immune response and is used to immunize animals during antibody production. - However, antigens are the **input** for antibody production, not the **product** of the hybridoma technique. *Cytokines* - **Cytokines** are signaling molecules involved in immune cell communication and regulation. - They are not produced by the hybridoma technique, which is specifically designed for **antibody production**.

Q: Which MRSA strain type is most commonly associated with hospital-acquired infections?

Phage type 80/81. ***Phage type 80/81*** - This **phage type**, particularly **epidemic methicillin-resistant *Staphylococcus aureus* (EMRSA) 15 and 16**, is historically and currently the most common cause of **hospital-acquired MRSA infections** worldwide. - It rapidly diversified and spread globally, becoming a significant nosocomial pathogen. *Phage type 83A* - While this phage type has been associated with **MRSA outbreaks**, it is not the most common strain type globally for hospital-acquired infections. - Its prevalence is more regional and sporadic compared to the widespread dominance of EMRSA 15/16. *Phage type 84* - **Phage type 84** is not widely recognized as a predominant strain associated with the majority of **hospital-acquired MRSA infections**. - Other, more virulent and successful clonal types have outcompeted it to become the most prevalent. *Phage type 85* - Similar to other less common types, **phage type 85** does not represent the major lineage responsible for the bulk of **hospital-acquired MRSA cases**. - The landscape of MRSA epidemiology is dominated by a few highly successful clonal complexes, of which 80/81 is a prime example.

Q: Which of the following stimulate adenylate cyclase with G-protein coupled action ?

Cholera toxin. ***Cholera toxin*** - Cholera toxin is a **G-protein-activating toxin** that irreversibly activates **adenylate cyclase**. - This leads to increased intracellular levels of **cAMP**, causing excessive fluid secretion into the intestinal lumen and severe diarrhea. *Shiga toxin* - Shiga toxin acts by inactivating the **60S ribosomal subunit**, thereby inhibiting protein synthesis in eukaryotic cells. - Its primary effect is **cytotoxicity**, not direct stimulation of adenylate cyclase. *Diphtheria toxin* - Diphtheria toxin inhibits **protein synthesis** by inactivating **elongation factor-2 (EF-2)** through ADP-ribosylation. - This toxin specifically targets host cells, leading to cellular death and tissue damage. *Pseudomonas toxin* - **Exotoxin A** produced by *Pseudomonas aeruginosa* also inhibits **protein synthesis** by ADP-ribosylating and inactivating **EF-2**, similar to diphtheria toxin. - It does not directly affect adenylate cyclase activity.

Q: Patient came from Nagaland and shows positive test with OXK antigen. Diagnosis is?

Scrub typhus. ***Scrub typhus*** - A **positive Weil-Felix test** for the **OXK antigen** is highly suggestive of scrub typhus, particularly if the patient is from an endemic region like Nagaland. - Scrub typhus is caused by **_Orientia tsutsugamushi_**, transmitted by **chiggers** (larval mites), often presenting with fever and an **eschar**. *Trench fever* - Caused by **_Bartonella quintana_** and transmitted by the **human body louse**. - It does not typically show a positive Weil-Felix test for the OXK antigen. *Endemic typhus* - Also known as **murine typhus**, it is caused by **_Rickettsia typhi_** and transmitted by **fleas** (e.g., rat flea). - While it causes a positive Weil-Felix test, it usually involves the **OX19 antigen**, not OXK. *Epidemic typhus* - Caused by **_Rickettsia prowazekii_** and transmitted by the **human body louse**. - It yields a positive Weil-Felix test for the **OX19 and OX2 antigens**, but typically not for OXK.

Question 1

Vaccines are available against which types of meningococcus?

Accepted Answer

Type A, B, C, W, and Y

Answer

Type A

Answer

Type B

Answer

Type A, B, and C

Question 2

Waterhouse-Friderichsen syndrome is seen in:

Accepted Answer

Neisseria meningitidis

Answer

Yersinia

Answer

Pseudomonas

Answer

Pneumococci

Question 3

Which of the following statements about Corynebacterium diphtheriae is NOT true?

Accepted Answer

Toxin mediated by chromosomal gene

Answer

Has metachromatic granules

Answer

Toxigenicity demonstrated by elek's test

Answer

Does not invade deeper tissues

Question 4

Pneumococcal vaccine is prepared from ?

Accepted Answer

Capsular polysaccharide

Answer

Cell surface antigen

Answer

Exotoxin

Answer

M protein

Question 5

What component is included in the vaccine against N-meningitidis?

Accepted Answer

Capsular polysaccharide (polysaccharide vaccine)

Answer

Killed whole-cell vaccine

Answer

Outer membrane protein (OMP)

Answer

Live attenuated vaccine

Question 6

Which organism is responsible for producing Draughtsman (Concentric Rings) on culture?

Accepted Answer

Bacillus anthracis

Answer

B. pertussis

Answer

H. ducreyi

Answer

Pneumococci

Question 7

What is the primary use of the Hybridoma technique?

Accepted Answer

Monoclonal antibodies

Answer

Antigen

Answer

Specific antibodies

Answer

Cytokines

Question 8

Which MRSA strain type is most commonly associated with hospital-acquired infections?

Accepted Answer

Phage type 80/81

Answer

Phage type 83A

Answer

Phage type 85

Answer

Phage type 84

Question 9

Which of the following stimulate adenylate cyclase with G-protein coupled action ?

Accepted Answer

Cholera toxin

Answer

Shiga toxin

Answer

Diphtheria toxin

Answer

Pseudomonas toxin

Question 10

Patient came from Nagaland and shows positive test with OXK antigen. Diagnosis is?

Accepted Answer

Scrub typhus

Answer

Trench fever

Answer

Endemic typhus

Answer

Epidemic typhus

NEET-PG 2013

Community Medicine

Internal Medicine

Microbiology