NEET-PG 2015 - Microbiology Practice Questions

Q: What is a common characteristic of the H5N1 and H7N7 strains of influenza?

Strains of avian influenza. ***Strains of avian influenza*** - Both **H5N1** and **H7N7** are well-known subtypes of the **influenza A virus** that primarily infect birds. - While they can infect humans, their natural reservoir and main hosts are **avian species**. *Frequent endemic infection in man* - These strains are not endemic in humans; human infections are typically **sporadic** and associated with close contact with infected birds. - They lack efficient **human-to-human transmission**, which prevents them from becoming endemic in the human population. *Have same frequency of antigenic variation* - Although both undergo **antigenic variation**, the specific frequency and patterns can differ between strains and are influenced by various factors, including their host range and circulation dynamics. - It is inaccurate to assume identical frequencies of **antigenic drift** and **shift** for different viral subtypes. *None of the options* - This option is incorrect because "Strains of avian influenza" is a correct and common characteristic shared by both H5N1 and H7N7.

Q: Capsular polysaccharide derived vaccine is available for all meningococci except?

Group B. ***Group B*** - The capsular polysaccharide of **Group B meningococci** is composed of **polysialic acid**, which is poorly immunogenic in humans because it structurally mimics human neural cell adhesion molecules. - Due to its **poor immunogenicity** and risk of autoantibody production, traditional polysaccharide vaccines are ineffective against Group B. *Group A* - Polysaccharide vaccines for **Group A meningococci** (e.g., in Menactra, Menveo) are effective in inducing a protective immune response. - Group A is a major cause of meningococcal disease, particularly in the **"meningitis belt"** of sub-Saharan Africa. *Group C* - **Capsular polysaccharide vaccines** are available and effective against Group C meningococcal disease, often included in quadrivalent formulations. - These vaccines elicit a robust **antibody response** against the Group C polysaccharide. *Group Y* - Vaccines containing the **capsular polysaccharide** of Group Y meningococci are effective and commonly included in quadrivalent vaccines. - Group Y is a significant cause of meningococcal disease, particularly in **North America and Europe**.

Q: A woman traveling from Bihar to Delhi is suspected to have Kala-azar. Suitable investigation is?

Rk-39 test. ***Rk-39 test*** - The **Rk-39 test** is a rapid diagnostic test highly sensitive and specific for detecting antibodies against the **kinesin-related protein K39** of *Leishmania donovani*, the causative agent of **Kala-azar (visceral leishmaniasis)**. - It is particularly useful in **endemic regions** like Bihar for quick and accurate diagnosis, especially in patients with suspected Kala-azar presenting with fever, splenomegaly, and pancytopenia. *P24 antigen* - **P24 antigen** testing is primarily used for the diagnosis of **HIV infection**. - It detects the **core protein p24** of the HIV virus, which is not relevant for the diagnosis of Kala-azar. *Combo RDT* - A **Combo RDT** (Rapid Diagnostic Test), without further specification, typically refers to tests for **malaria**, which detect antigens like **HRP-2** and **aldolase**. - While RDTs are used for parasitic diseases, this general term does not specifically refer to a test for **Kala-azar**. *HRP-2 antigen* - **HRP-2 (Histidine-rich protein 2) antigen** is a specific marker for **Plasmodium falciparum**, used in the diagnosis of **malaria**. - It is not associated with the diagnosis of **Kala-azar**, which is caused by *Leishmania donovani*.

Q: Which organism is considered the PRIMARY prototype for Ziehl-Neelsen (acid-fast) staining identification?

Mycobacterium tuberculosis. ***Mycobacterium tuberculosis*** - The **Ziehl-Neelsen (ZN) stain** is the classic **acid-fast staining** technique used to identify **Mycobacterium species**, particularly **M. tuberculosis** - **Mycobacteria** possess high content of **mycolic acid** (60-90 carbon fatty acids) in their cell wall, making them resistant to decolorization by acid-alcohol - After staining with **carbol fuchsin** (heated), acid-fast bacilli retain the **red/pink color** while non-acid-fast organisms are decolorized and counterstained blue - M. tuberculosis is the **prototype organism** for acid-fast staining and remains the primary clinical application of ZN stain - **Note:** Modified ZN stain (using weaker 1% H2SO4) is used for **weakly acid-fast organisms** like Nocardia and Cryptosporidium *Streptococcus pneumoniae* - This is a **Gram-positive coccus** identified by **Gram staining**, not acid-fast staining - Appears as lancet-shaped diplococci on Gram stain - Lacks mycolic acid in cell wall and cannot retain carbol fuchsin after acid-alcohol decolorization *Escherichia coli* - This is a **Gram-negative bacillus** with thin peptidoglycan layer and outer membrane - Identified by **Gram staining** (appears pink/red) and biochemical tests - Not acid-fast and would be completely decolorized in ZN staining procedure *Clostridium difficile* - This is an **anaerobic, Gram-positive, spore-forming bacillus** - Identified by **Gram staining** and anaerobic culture - Lacks mycolic acid and acid-fast properties, making it unsuitable for ZN staining

Q: Viral DNA is integrated into Bacterial DNA in:

Lysogenic cycle. ***Lysogenic cycle*** - In the **lysogenic cycle**, the **bacteriophage DNA integrates** into the host bacterial chromosome, becoming a **prophage**. - This integration allows the viral genome to be **replicated along with the host DNA** without immediately lysing the cell. *Bacterial transduction* - **Transduction** involves the transfer of **bacterial DNA** from one bacterium to another via a bacteriophage, not the integration of viral DNA into the host genome. - While phages are involved, the primary event is the accidental packaging and transfer of bacterial genes, not viral integration into the host for replication. *Bacterial transformation* - **Transformation** is the process where bacteria take up **naked DNA from their environment** and incorporate it into their own genome. - This DNA is typically from another bacterium or is artificially introduced, not viral DNA undergoing a natural integration process within the cell. *Bacterial conjugation* - **Conjugation** is the transfer of genetic material (usually a **plasmid**) between bacteria through direct cell-to-cell contact, mediated by a **pilus**. - This process involves the transfer of bacterial or plasmid DNA, not the integration of a viral genome into the host chromosome.

Q: Brill-Zinsser disease is a recrudescent form of which infection?

Recrudescence of R prowazekii infection. **Recrudescence of R prowazekii infection** - Brill-Zinsser disease is a **late-onset complication** of **epidemic typhus**, caused by *Rickettsia prowazekii*. - It occurs years after the initial infection, due to **reactivation of dormant bacteria** in the body. *Recrudescence of R typhi infection* - *Rickettsia typhi* causes **murine typhus**, but its recrudescent form is not referred to as Brill-Zinsser disease. - Murine typhus is typically a **milder disease** compared to epidemic typhus. *Recrudescence of Coxiella burnetii infection* - *Coxiella burnetii* causes **Q fever**, which can have a chronic form but is not a recrudescence of a typhus infection. - Q fever presents with different clinical manifestations, such as **endocarditis** or **hepatitis**, not typically a rash or neurological symptoms seen in typhus. *None of the options* - This option is incorrect because the specific recrudescent form described in the question clearly points to *Rickettsia prowazekii*.

Q: Primary complex of M bovis involves:

Tonsil and intestine. ***Tonsil and intestine*** - *Mycobacterium bovis* is primarily transmitted through **consumption of contaminated milk and dairy products**, making the **alimentary tract** the main route of infection - The primary complex (Ghon complex) involves the **initial site of infection plus regional lymph nodes** - In alimentary tuberculosis, the organisms enter through the **intestinal mucosa** (Peyer's patches) or **tonsillar tissue**, creating foci with associated mesenteric or cervical lymphadenopathy - Both tonsils and intestines are part of the **alimentary system**, representing the typical primary complex for M. bovis in humans *Tonsil and lung* - This incorrectly combines **two different routes of entry** (alimentary and respiratory) - A primary complex involves a **single portal of entry**, not multiple unrelated organ systems - While M. bovis can rarely cause pulmonary TB through inhalation, this would create a separate lung + hilar node complex, not a combined tonsil-lung complex *Tonsil and skin* - **Skin involvement** requires direct inoculation through cuts or abrasions and does not form a primary complex with tonsillar infection - These represent different portals of entry and would not occur together as a primary complex *Skin and Intestine* - **Skin infection** by M. bovis is rare and requires occupational exposure with direct inoculation (e.g., veterinarians, butchers) - This incorrectly pairs two different routes of infection that would not form a single primary complex

Q: Salmonella and Shigella can be differentiated from other Enterobacteriaceae members by isolation on:

XLD agar. ***XLD agar*** - **Xylose Lysine Deoxycholate (XLD) agar** is a selective and differential medium used to isolate and identify *Salmonella* and *Shigella* species from other Enterobacteriaceae. - It differentiates *Salmonella* and *Shigella* based on their ability to ferment **xylose**, decarboxylate **lysine**, and produce **hydrogen sulfide (H2S)**. *MacConkey agar* - **MacConkey agar** is a selective and differential medium used to isolate Gram-negative bacteria and differentiate them based on **lactose fermentation**. - While it can grow *Salmonella* and *Shigella* (which are non-lactose fermenters), it does not specifically differentiate them from other non-lactose fermenting Enterobacteriaceae. *Mannitol salt agar* - **Mannitol salt agar (MSA)** is a selective and differential medium primarily used for the isolation of **staphylococci**. - It is highly selective due to its high salt concentration and differentiates staphylococci based on their ability to ferment **mannitol**. *BCYE medium* - **Buffered Charcoal Yeast Extract (BCYE) medium** is a specialized enrichment medium used for the isolation of **Legionella species**. - It provides specific nutrients required for the growth of *Legionella* and is not suitable for differentiating *Salmonella* and *Shigella* from other Enterobacteriaceae.

Q: Which of the following statements about anthrax toxin is false?

Inhibits protein synthesis. ***Inhibits protein synthesis*** - Anthrax toxin, specifically the **lethal factor (LF)**, is a **zinc-dependent metalloprotease** that cleaves and inactivates **mitogen-activated protein kinase kinase (MAPKKs)**, leading to cell death, not directly inhibiting protein synthesis. - The **edema factor (EF)** component of the toxin is an **adenylate cyclase** that increases **intracellular cyclic AMP (cAMP)**, which also does not directly inhibit protein synthesis. *Has three components* - Anthrax toxin is indeed composed of three distinct proteins: **protective antigen (PA)**, **edema factor (EF)**, and **lethal factor (LF)**. - PA is necessary for EF and LF to enter host cells, while EF causes edema and LF is responsible for cytotoxicity. *Increase cAMP* - The **edema factor (EF)** component of anthrax toxin is a **calmodulin-dependent adenylate cyclase**. - Once inside the cell, EF converts **ATP to cyclic AMP (cAMP)**, leading to increased intracellular cAMP levels, which disrupts water homeostasis and causes edema. *Coded by plasmid* - The genes encoding the anthrax toxin components (PA, EF, and LF) are located on a large plasmid known as **pXO1**. - This plasmid, along with another plasmid (pXO2) carrying genes for the capsule, is crucial for the full virulence of *Bacillus anthracis*.

Q: Naegler's reaction is due to:

Lecithinase. ***Lecithinase*** - The **Naegler reaction** is a bacterial identification test used to detect the production of **lecithinase** (also known as alpha-toxin) by certain bacteria, particularly *Clostridium perfringens*. - This enzyme hydrolyzes **lecithin** (a lipid found in egg yolk), resulting in a visible opaque precipitate around the bacterial colonies on egg yolk agar. *Coagulase* - **Coagulase** is an enzyme produced by some bacteria (e.g., *Staphylococcus aureus*) that causes the coagulation of blood plasma. - While it is an important virulence factor, it is not involved in the **Naegler reaction**. *Hyaluronidase* - **Hyaluronidase** is an enzyme that breaks down **hyaluronic acid**, a component of connective tissue, facilitating the spread of bacteria. - It is often referred to as a **spreading factor** but is not detected by the **Naegler reaction**. *None of the options* - This option is incorrect because **Lecithinase** is directly responsible for the **Naegler reaction**.

Question 1

What is a common characteristic of the H5N1 and H7N7 strains of influenza?

Accepted Answer

Strains of avian influenza

Answer

Frequent endemic infection in man

Answer

Have same frequency of antigenic variation

Answer

None of the options

Question 2

Capsular polysaccharide derived vaccine is available for all meningococci except?

Accepted Answer

Group B

Answer

Group C

Answer

Group Y

Answer

Group A

Question 3

A woman traveling from Bihar to Delhi is suspected to have Kala-azar. Suitable investigation is?

Accepted Answer

Rk-39 test

Answer

P24 antigen

Answer

Combo RDT

Answer

HRP-2 antigen

Question 4

Which organism is considered the PRIMARY prototype for Ziehl-Neelsen (acid-fast) staining identification?

Accepted Answer

Mycobacterium tuberculosis

Answer

Escherichia coli

Answer

Streptococcus pneumoniae

Answer

Clostridium difficile

Question 5

Viral DNA is integrated into Bacterial DNA in:

Accepted Answer

Lysogenic cycle

Answer

Bacterial transduction

Answer

Bacterial transformation

Answer

Bacterial conjugation

Question 6

Brill-Zinsser disease is a recrudescent form of which infection?

Accepted Answer

Recrudescence of R prowazekii infection

Answer

Recrudescence of R typhi infection

Answer

None of the options

Answer

Recrudescence of Coxiella burnetii infection

Question 7

Primary complex of M bovis involves:

Accepted Answer

Tonsil and intestine

Answer

Tonsil and skin

Answer

Tonsil and lung

Answer

Skin and Intestine

Question 8

Salmonella and Shigella can be differentiated from other Enterobacteriaceae members by isolation on:

Accepted Answer

XLD agar

Answer

MacConkey agar

Answer

Mannitol salt agar

Answer

BCYE medium

Question 9

Which of the following statements about anthrax toxin is false?

Accepted Answer

Inhibits protein synthesis

Answer

Increase cAMP

Answer

Has three components

Answer

Coded by plasmid

Question 10

Naegler's reaction is due to:

Accepted Answer

Lecithinase

Answer

Coagulase

Answer

Hyaluronidase

Answer

None of the options

NEET-PG 2015 — Microbiology