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?
Heating a bacterial sample at 60°C for 30 minutes would isolate which of the following?
Which of the following viruses is a member of the Herpesviridae family?
HIV envelope is formed by:
Which HIV virus is associated with a higher transmission rate and virulence?
Which strain of the Influenza A virus, not of human origin, has the highest pandemic potential?
Which of the following can infect the ovary?
NEET-PG 2015 - Microbiology NEET-PG Practice Questions and MCQs
Question 51: 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 52: 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 53: 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 54: 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.
Question 55: Heating a bacterial sample at 60°C for 30 minutes would isolate which of the following?
- A. Staphylococci
- B. Micrococci
- C. Streptococci
- D. Enterococcus species (Correct Answer)
Explanation: ***Enterococcus species*** - **Enterococcus species** are known for their ability to survive harsh conditions, including temperatures of **60°C for at least 30 minutes**. - This characteristic is often used in laboratories for selective isolation and differentiation from other bacteria like streptococci and staphylococci. *Staphylococci* - While some staphylococci are quite hardy, most species, including *Staphylococcus aureus*, typically do not tolerate **60°C for 30 minutes** as well as enterococci. - Exposure to this temperature would likely significantly reduce the viability of most staphylococcal species, making their isolation difficult. *Micrococci* - **Micrococci** are generally less heat-tolerant than enterococci and would likely be killed or severely inhibited by exposure to **60°C for 30 minutes**. - They are generally susceptible to temperatures that would be survivable for thermoduric bacteria. *Streptococci* - Most **streptococcal species** are not highly resistant to heat and would be inactivated by prolonged exposure to **60°C**. - This heat treatment is often used in laboratory procedures to differentiate enterococci from other streptococci, as enterococci were historically classified as Group D streptococci.
Question 56: Which of the following viruses is a member of the Herpesviridae family?
- A. Variola
- B. Adenovirus
- C. HPV
- D. Herpes Simplex Virus (Correct Answer)
Explanation: ***Herpes Simplex Virus*** - **Herpes Simplex Virus (HSV)** is the type species of the *Herpesviridae* family, which includes other common human pathogens such as **cytomegalovirus** and **Epstein-Barr virus**. - Members of this family are characterized by a **double-stranded DNA genome**, an icosahedral capsid, and an envelope, and they typically cause **latent infections**. *Variola* - **Variola virus** is a member of the *Poxviridae* family, known for causing **smallpox**, a historically devastating disease. - Unlike herpesviruses, poxviruses are **large and complex DNA viruses** that replicate entirely in the cytoplasm of infected cells. *Adenovirus* - **Adenovirus** belongs to the *Adenoviridae* family and is a **non-enveloped DNA virus** known for causing a variety of conditions, including respiratory infections and conjunctivitis. - Its structure and replication cycle differ significantly from the enveloped *Herpesviridae*. *HPV* - **HPV (Human Papillomavirus)** is a member of the *Papillomaviridae* family, which are small **non-enveloped DNA viruses** associated with warts and certain cancers. - It is distinct from herpesviruses in its genomic organization, capsid structure, and disease manifestations.
Question 57: HIV envelope is formed by:
- A. Host cell
- B. Virus
- C. Both (Correct Answer)
- D. None of the options
Explanation: ***Both (Correct Answer)*** - The HIV envelope is a **composite structure** derived from both host and viral components - The **lipid bilayer** is acquired from the **host cell membrane** during viral budding - **Viral glycoproteins (gp120 and gp41)** encoded by the viral genome are inserted into this host-derived membrane - This makes the envelope a true hybrid structure essential for viral infectivity *Host cell (Incomplete)* - While the **lipid bilayer** of the envelope comes from the host cell membrane during budding, this alone does not form a functional envelope - The host cell provides the membrane scaffold but lacks the viral glycoproteins necessary for receptor binding and cell entry - Without viral proteins, the envelope cannot mediate infection *Virus (Incomplete)* - The virus encodes essential **envelope glycoproteins** (gp120 for receptor binding, gp41 for membrane fusion) - However, the virus does **not synthesize the lipid bilayer** itself - The viral genome lacks genes for lipid synthesis; the membrane must be acquired from the host *None of the options* - This is incorrect as the HIV envelope clearly requires contributions from **both** the host cell (lipid membrane) and the virus (glycoproteins)
Question 58: Which HIV virus is associated with a higher transmission rate and virulence?
- A. Both have similar risks
- B. It depends on individual factors
- C. HIV-2
- D. HIV-1 (Correct Answer)
Explanation: ***HIV-1*** - **HIV-1** is responsible for the vast majority of HIV infections worldwide and is known for its **higher virulence** and more rapid progression to AIDS. - It also has a **higher transmission rate** compared to HIV-2, contributing to its global prevalence. *HIV-2* - **HIV-2** is less virulent and has a **slower progression** to AIDS compared to HIV-1. - Its transmission rate is **lower** than HIV-1, and it is primarily concentrated in West Africa. *Both have similar risks* - This statement is incorrect because **HIV-1 and HIV-2 differ significantly** in their transmission rates, virulence, and disease progression. - **HIV-1** poses a much greater global health burden due to its higher infectivity and pathology. *It depends on individual factors* - While individual factors can influence disease progression, the intrinsic characteristics of **HIV-1** and **HIV-2** (such as transmissibility and virulence) are distinct and not solely dependent on the host. - The inherent biological differences between the two viruses are the primary determinants of their differential impact.
Question 59: Which strain of the Influenza A virus, not of human origin, has the highest pandemic potential?
- A. H1N1
- B. H9N2
- C. H2N2
- D. H5N1 (Correct Answer)
Explanation: ***H5N1*** - The **H5N1 avian influenza virus** is widely considered to have high pandemic potential due to its ability to cause severe disease and high mortality in humans, despite limited human-to-human transmission. - It circulates extensively in **poultry populations**, providing ample opportunity for zoonotic spillover. *H1N1* - While H1N1 caused the **2009 swine flu pandemic**, the question specifies a strain "not of human origin" with high pandemic potential, and H1N1 is an avian-origin reassortant that adapted to humans. - Current circulating seasonal H1N1 strains already have some human immunity, reducing their pandemic potential. *H2N2* - The **H2N2 strain** caused the 1957 "Asian Flu" pandemic, and current human populations have some immunity due to previous exposure to related strains in circulation. - It is no longer circulating in humans and its pandemic potential is lower compared to novel highly pathogenic avian strains like H5N1. *H9N2* - **H9N2** is a low-pathogenic avian influenza virus that has caused sporadic human infections, primarily in agricultural workers. - While it has zoonotic potential, its infections in humans are typically mild and its capacity for sustained human-to-human transmission remains very limited, indicating lower pandemic potential than H5N1.
Question 60: Which of the following can infect the ovary?
- A. Mumps virus (Correct Answer)
- B. Epstein-Barr Virus (EBV)
- C. Cytomegalovirus (CMV)
- D. Measles virus
Explanation: ***Mumps virus*** - The mumps virus can cause **oophoritis** (inflammation of the ovary) in post-pubertal females, though it is less common than orchitis in males. - Oophoritis typically presents with **lower abdominal pain** and tenderness, often accompanied by fever and other mumps symptoms like parotitis. *Epstein-Barr Virus (EBV)* - While EBV causes **infectious mononucleosis** and is associated with various lymphomas and nasopharyngeal carcinoma, it is not a primary cause of direct ovarian infection. - EBV primarily targets **B lymphocytes** and epithelial cells, and ovarian involvement is not a typical manifestation. *Cytomegalovirus (CMV)* - CMV can cause a wide range of infections, particularly in **immunocompromised individuals** and neonates, leading to congenital abnormalities. - Although CMV can infect many organs, direct infection of the ovary leading to oophoritis is **extremely rare** and not a recognized clinical entity. *Measles virus* - The measles virus primarily causes a systemic infection characterized by a **maculopapular rash**, fever, cough, coryza, and conjunctivitis. - While it can lead to complications such as pneumonia or encephalitis, **ovarian involvement or oophoritis** is not a known or common complication of measles.