NEET-PG 2012 - Microbiology Practice Questions

Q: What is the role of p24 in HIV?

Core antigen of HIV. ***Core antigen of HIV*** - **p24** is a **structural protein** that forms the viral capsid, which is the shell enclosing the genetic material of the virus. - Due to its abundance and immunogenicity, **p24** serves as a crucial **biomarker** for initial **HIV infection** and is targeted in diagnostic tests. *Envelop antigen in HIV* - The **envelope antigens** of HIV are typically **glycoproteins** like **gp120** and **gp41**, which are involved in viral attachment and entry into host cells. - These envelope proteins are distinct from **p24**, which is an internal core protein. *Genome of HIV* - The **genome of HIV** consists of **two copies of single-stranded RNA**, not a protein. - This **RNA genome** is contained within the viral capsid, which is primarily composed of **p24 protein**. *Shell antigen* - While **p24** does form a "shell" (the capsid) around the viral genome, the term **shell antigen** is not a standard specific classification in virology for p24. - The more precise term for its location and function is **core antigen**.

Q: Which of the following statements is true regarding Diphyllobothrium?

The operculated egg is a diagnostic feature. ***The operculated egg is a diagnostic feature*** - *Diphyllobothrium latum*, also known as the **fish tapeworm**, produces characteristic **operculated eggs** that are oval-shaped with an operculum (cap) at one end and a small knob at the other. - The presence of these **unembryonated eggs** in stool samples is the primary diagnostic method for diphyllobothriasis. *Humans are the only definitive host* - While humans are common definitive hosts, other **fish-eating mammals** such as bears, dogs, and cats can also serve as definitive hosts for *Diphyllobothrium latum*. - The definitive host is where the **adult worm resides** and reproduces sexually. *Vitamin B12 deficiency always occurs in infection* - **Vitamin B12 deficiency (megaloblastic anemia)** is a known complication of *Diphyllobothrium latum* infection, as the worm competes for B12 in the host's intestine. - However, it does **not occur in all infected individuals**; it is estimated to affect a significant minority, typically those with heavy worm burdens or prolonged infection, and can be influenced by dietary intake. *Fish are definitive hosts* - Fish (specifically freshwater fish like pike, perch, and salmon) act as **second intermediate hosts** for *Diphyllobothrium latum*, carrying the **plerocercoid larvae**. - **Humans and other fish-eating mammals** are the definitive hosts, where the plerocercoid larvae mature into adult tapeworms in the small intestine.

Q: Influenza virus culture is done on ?

Allantoic cavity. ***Allantoic cavity*** - The **allantoic cavity** of embryonated chicken eggs is the standard and most effective site for isolating and propagating **influenza viruses** for vaccine production and research. - This cavity provides an optimal environment for viral replication, particularly yielding high titers of **hemagglutinin**, a key influenza antigen. *Chorioallantoic membrane* - While embryonated eggs are used for virus culture, the **chorioallantoic membrane (CAM)** is primarily used for cultivating viruses that produce **pocks** (visible lesions), such as Vaccinia and Herpes Simplex Virus. - Influenza virus growth on the CAM is less efficient and typically doesn't produce distinct pocks, making it unsuitable for high-yield propagation compared to the allantoic cavity. *Yolk sac* - The **yolk sac** of embryonated eggs is ideal for growing viruses or bacteria that require a **lipid-rich environment** and replicate intracellularly, such as Chlamydia or Rickettsia. - It is not the preferred site for influenza virus isolation or proliferation due to suboptimal conditions for viral replication and lower viral yields. *All of the options* - While all these sites are components of an embryonated chicken egg, each serves as a host for different types of microorganisms or for specific purposes in virology. - For **influenza virus culture**, the **allantoic cavity** is the specifically utilized site for optimal growth and high viral yield.

Q: Virus quantification is done by-

Plaque assay. ***Plaque assay*** - The **plaque assay** is a widely used and quantitative method to determine the number of **infectious viral particles** in a sample. - It involves infecting a monolayer of host cells with serially diluted virus samples, leading to the formation of visible **plaques** (zones of lysed cells), which are then counted. *Studying virus-cell interactions* - Studying **virus-cell interactions** helps understand the mechanisms of viral entry, replication, and egress but does not directly quantify the number of viral particles. - While critical for understanding viral pathogenesis, this approach is qualitative rather than quantitative in nature. *Visualizing virus particles* - **Visualizing virus particles** (e.g., using electron microscopy) allows for counting individual virions, but it quantifies both infectious and non-infectious particles. - This method provides a total particle count rather than a measure of infectivity. *Virus isolation using eggs* - **Virus isolation using eggs** (e.g., embryonated chicken eggs) is a method for propagating and isolating certain viruses, particularly influenza. - While it can be optimized for relative comparisons, it is not primarily a direct quantitative method like the plaque assay for determining infectious viral titers.

Q: Which of the following organisms does not enter through abrasions in the skin?

C hominis. ***Chryseobacterium hominis*** - **Chryseobacterium hominis** is primarily a cause of **nosocomial infections**, particularly in immunocompromised patients, and typically enters the body via **medical devices or respiratory route**, not skin abrasions. - It is known to colonize humid environments and medical equipment, leading to **bacteremia**, **meningitis**, or **pneumonia**. - This organism is transmitted through contaminated medical equipment, ventilators, or via the respiratory tract, distinguishing it from the other options. *Erysipelothrix rhusiopathiae* - This organism is a common cause of **erysipelas** or **erysipeloid** in humans, often contracted through contact with infected animals or animal products via **minor skin abrasions**. - The infection typically presents as a **painful, violaceous, spreading skin lesion** at the site of inoculation. - Common in fish handlers, butchers, and veterinarians who sustain occupational skin injuries. *Eikenella corrodens* - **Eikenella corrodens** is a gram-negative rod that is part of the normal oral flora and often causes infections following **human bites** or **fist fights** (clenched-fist injuries), where it enters through **skin abrasions or breaks**. - It is notorious for causing **osteomyelitis** and **abscesses** subsequent to these types of injuries. *Chromobacterium violaceum* - **Chromobacterium violaceum** is a rare but highly pathogenic bacterium found in soil and water in tropical and subtropical regions, entering the body through **breaks in the skin**, such as cuts or abrasions. - Infections are severe and can lead to **sepsis**, **multiple organ abscesses**, and a high mortality rate due to its production of **violacein** and other toxins.

Q: Which of the following viruses is classified as a poxvirus?

Variola. ***Variola virus*** - **Variola virus** is the causative agent of **smallpox**, a historically significant and highly contagious disease. - It belongs to the **Orthopoxvirus** genus within the **Poxviridae family**, characterized by its large, brick-shaped virion and dsDNA genome. *Coxsackie virus* - **Coxsackieviruses** are part of the **Picornaviridae family**, specifically the **Enterovirus** genus. - They are known to cause a range of diseases including **hand-foot-and-mouth disease**, myocarditis, and aseptic meningitis, and are much smaller than poxviruses. *ECHO virus* - **Echoviruses** (Enteric Cytopathic Human Orphan viruses) are also members of the **Picornaviridae family** and the **Enterovirus** genus. - They are associated with diseases such as **aseptic meningitis**, gastroenteritis, and respiratory infections, completely distinct from poxviruses. *HSV (Herpes Simplex Virus)* - **Herpes Simplex Viruses** belong to the **Herpesviridae family**, characterized by a **linear dsDNA genome** and an enveloped icosahedral capsid. - They cause diseases like **oral and genital herpes** and are structurally and genetically distinct from poxviruses.

Q: Which of the following statements about trematodes is true?

Two hosts required. ***Two hosts required (Correct)*** - Trematodes typically require at least **two hosts** to complete their life cycle: an intermediate host (usually a **snail**) and a definitive host (a vertebrate). - This complex lifecycle involving multiple hosts is a characteristic feature of **flukes**. - This is a fundamental distinguishing feature that separates trematodes from some other helminths. *Segmented (Incorrect)* - Trematodes (flukes) have **unsegmented, leaf-shaped or cylindrical bodies**, unlike cestodes (tapeworms) which are segmented. - The absence of body segmentation is a key morphological distinction from other helminths. *Anus present (Incorrect)* - Trematodes have an **incomplete digestive system** with a mouth and an esophagus, but **no anus**. - Waste products are expelled back through the **mouth**. - This blind-ending gut is characteristic of the class Trematoda. *Body cavity present (Incorrect)* - Trematodes are **acoelomates**, meaning they lack a true fluid-filled body cavity (coelom). - Their internal organs are embedded in **parenchymatous tissue** filling the space between body wall and organs.

Q: Which disease is classified as 'multibacillary'?

Leprosy. **Leprosy** - Leprosy, caused by *Mycobacterium leprae*, is classified by the **WHO** into **paucibacillary (PB)** and **multibacillary (MB)** forms based on bacterial load and number of skin lesions. - **Multibacillary leprosy** is defined as having more than 5 skin lesions with positive skin smears, requiring a longer treatment regimen (12 months of multidrug therapy with rifampicin, dapsone, and clofazimine). - This classification is specific to **leprosy** and is crucial for determining appropriate treatment duration and drug combinations. *Tuberculosis* - Tuberculosis is classified by **anatomical location** (pulmonary vs. extrapulmonary), **drug susceptibility** (drug-sensitive vs. drug-resistant), or **smear status** (smear-positive vs. smear-negative). - The term **'multibacillary'** is not used in TB classification, making this an incorrect option. *Trachoma* - Trachoma is a chronic **keratoconjunctivitis** caused by *Chlamydia trachomatis*, classified by **clinical stages** (TF, TI, TS, TT, CO) according to the WHO simplified grading system. - The paucibacillary/multibacillary classification does **not apply** to trachoma. *Tetanus* - Tetanus is a **toxin-mediated disease** caused by *Clostridium tetani*, manifesting as muscle spasms and lockjaw. - Classification is based on **clinical severity** (localized, generalized, cephalic, neonatal), not bacterial load, making the term 'multibacillary' inapplicable.

Q: Which of the following statements about interferons is true?

Interferons inhibit viral replication in host cells.. **Interferons inhibit viral replication in host cells.** - Interferons are a crucial part of the **innate immune response** against viral infections. - They work by inducing an **antiviral state** in neighboring uninfected cells, preventing viral replication. - Interferons are **non-specific** antiviral cytokines with broad-spectrum activity. *Interferons are specific for particular viruses.* - This is incorrect. Interferons are **virus-non-specific** in their antiviral action. - While their production is triggered by viral infection, they can inhibit replication of various different viruses. - This broad-spectrum activity is a key feature distinguishing them from antibodies (which are specific). *Interferons have no effect on viral infections.* - This is false. Interferons are potent **antiviral cytokines** essential for host defense against viruses. - They activate immune cells (NK cells, macrophages) and induce expression of genes that inhibit viral processes. *Interferons are synthetic antiviral agents.* - This is incorrect. Interferons are **naturally produced proteins** by the body's cells (leukocytes, fibroblasts, dendritic cells) in response to viral infections. - While recombinant interferons are used therapeutically, interferons are biological molecules, not synthetic drugs.

Q: What is the primary function of the Nef gene in HIV?

Enhancing viral pathogenesis. ***Enhancing viral pathogenesis*** - The **Nef protein** is critical for efficient viral replication and disease progression in HIV-infected individuals, significantly increasing **viral load** and contributing to immune evasion. - It achieves this by downregulating **CD4** and **MHC class I** molecules on the surface of infected cells, thereby preventing immune recognition and increasing viral infectivity. *Enhancing the expression of host genes* - While Nef interacts with various host proteins, its primary function is not to globally enhance the expression of host genes but rather to modulate specific host pathways to favor viral replication. - Instead, Nef often leads to **downregulation** of specific host proteins important for immune response, such as CD4 and MHC class I. *Decreasing viral replication* - Nef's role is to **increase**, not decrease, viral replication and spread within the host. - Viruses lacking a functional Nef gene show **attenuated replication** in vivo and often reduced pathogenicity. *Promoting host cell apoptosis* - While Nef can influence cellular processes, its direct and primary function is not to promote host cell apoptosis. - In fact, Nef can sometimes prevent early apoptosis of infected cells, allowing more time for virus production and release, thereby contributing to viral persistence.

Question 1

What is the role of p24 in HIV?

Accepted Answer

Core antigen of HIV

Answer

Envelope antigen in HIV

Answer

Genome of HIV

Answer

Shell antigen

Question 2

Which of the following statements is true regarding Diphyllobothrium?

Accepted Answer

The operculated egg is a diagnostic feature

Answer

Humans are the only definitive host

Answer

Vitamin B12 deficiency always occurs in infection

Answer

Fish are definitive hosts

Question 3

Influenza virus culture is done on ?

Accepted Answer

Allantoic cavity

Answer

Chorioallantoic membrane

Answer

Yolk sac

Answer

All of the options

Question 4

Virus quantification is done by-

Accepted Answer

Plaque assay

Answer

Studying virus-cell interactions

Answer

Visualizing virus particles

Answer

Virus isolation using eggs

Question 5

Which of the following organisms does not enter through abrasions in the skin?

Accepted Answer

C hominis

Answer

E rhusiopathiae

Answer

E corrodens

Answer

C violaceum

Question 6

Which of the following viruses is classified as a poxvirus?

Accepted Answer

Variola

Answer

Coxsackie

Answer

ECHO

Answer

HSV

Question 7

Which of the following statements about trematodes is true?

Accepted Answer

Two hosts required

Answer

Segmented

Answer

Anus present

Answer

Body cavity present

Question 8

Which disease is classified as 'multibacillary'?

Accepted Answer

Leprosy

Answer

Tuberculosis

Answer

Trachoma

Answer

Tetanus

Question 9

Which of the following statements about interferons is true?

Accepted Answer

Interferons inhibit viral replication in host cells.

Answer

Interferons are specific for particular viruses.

Answer

Interferons have no effect on viral infections.

Answer

Interferons are synthetic antiviral agents.

Question 10

What is the primary function of the Nef gene in HIV?

Accepted Answer

Enhancing viral pathogenesis

Answer

Enhancing the expression of host genes

Answer

Decreasing viral replication

Answer

Promoting host cell apoptosis

NEET-PG 2012 — Microbiology