NEET-PG 2012 - Microbiology Practice Questions

Q: Which type of vaccine is used for chicken pox?

Live vaccine. ***Live vaccine*** - The chickenpox vaccine (Varicella vaccine) is a **live-attenuated vaccine**, meaning it contains a weakened form of the **Varicella-zoster virus** (Oka strain). - This weakened virus can still replicate in the body, stimulating a strong and long-lasting immune response similar to natural infection but without causing severe disease. *Killed vaccine* - **Killed (inactivated) vaccines** use viruses or bacteria that have been inactivated through heat or chemicals, making them unable to replicate. - While effective for some diseases (e.g., inactivated polio, influenza), they typically require **multiple doses** and might provide less durable immunity compared to live vaccines. *Conjugated vaccine* - **Conjugated vaccines** are designed to improve the immune response to polysaccharide antigens (e.g., bacterial capsules) by linking them to a carrier protein. - This technology is primarily used for **bacterial infections** like *Haemophilus influenzae* type b (Hib) or pneumococcal disease, not viral illnesses like chickenpox. *Toxoid vaccine* - **Toxoid vaccines** contain inactivated bacterial toxins (toxoids) rather than the whole organism. - Examples include **tetanus and diphtheria vaccines**, which protect against diseases caused by bacterial toxins, not viral infections like chickenpox.

Q: Which of the following statements is false regarding yersiniosis?

Caused by Yersinia pestis. ***Caused by Yersinia pestis*** - **Yersinia pestis** is the causative agent of **plague**, not typical yersiniosis affecting the gastrointestinal tract. - Yersiniosis generally refers to infections caused by other *Yersinia* species like *Y. enterocolitica* and *Y. pseudotuberculosis*. *Gram-negative bacillus* - *Yersinia* species, including *Y. enterocolitica* and *Y. pseudotuberculosis*, are indeed **Gram-negative bacilli**. - This characteristic is fundamental to their classification and bacterial structure. *Caused by Yersinia pseudotuberculosis* - **Yersinia pseudotuberculosis** is a recognized cause of **yersiniosis**, particularly affecting children. - It can cause symptoms such as **abdominal pain** and **mesenteric lymphadenitis**, mimicking appendicitis. *Caused by Yersinia enterocolitica* - **Yersinia enterocolitica** is the **most common cause of yersiniosis** in humans. - It is responsible for a range of symptoms including **gastroenteritis**, **acute enteritis**, and **mesenteric lymphadenitis**.

Q: Which part of bacteria is most antigenic?

Lipopolysaccharide. ***Lipopolysaccharide (LPS)*** - The **O antigen** (polysaccharide component of LPS) in Gram-negative bacteria is one of the **most antigenic** bacterial components - Highly **immunogenic**, inducing strong antibody responses (both IgM and IgG) - Used as the basis for **serological typing** of Gram-negative bacteria (e.g., E. coli O157:H7) - The polysaccharide chains are structurally diverse with multiple epitopes, creating strain-specific immunity - While lipid A component has endotoxin activity, the polysaccharide portion is the primary antigenic determinant *Protein coat* - Bacterial **surface proteins** (flagella, pili, outer membrane proteins) are indeed antigenic - However, **polysaccharides** (including capsular polysaccharides and LPS) are classically considered more potent antigens - The term "protein coat" is also somewhat non-specific in bacteriology *Nucleic acid* - **Nucleic acids** (DNA, RNA) are generally **poor antigens** on their own - Not readily accessible to antibodies as they are intracellular - Can act as pathogen-associated molecular patterns (PAMPs) for innate immunity via TLRs, but are not major antibody targets *Lipids* - **Lipids** alone are generally **non-immunogenic** due to lack of structural complexity - Too small and lack sufficient epitopes to stimulate B cell responses effectively - May act as **haptens** requiring conjugation to carrier proteins

Q: Cercariae are the infective form of which of the following parasites?

Schistosoma hematobium. ***Schistosoma hematobium*** - **Cercariae** are the motile, free-swimming larval stage of **Schistosoma** species, including *S. hematobium* - They **actively penetrate human skin** to initiate infection, making cercariae the infective form for humans *Paragonimus westermani* - The infective form for humans is **metacercariae**, which are ingested by consuming insufficiently cooked **crabs or crayfish** - Cercariae develop into metacercariae in secondary intermediate hosts (crustaceans) *Fasciola hepatica* - Humans are infected by ingesting **metacercariae** present on aquatic vegetation, such as **watercress** - Cercariae encyst on plants to form metacercariae, not directly infective *Taenia solium* - The infective forms are **cysticerci** in undercooked pork (for adult tapeworm) or **embryonated eggs** (causing cysticercosis) - This cestode has a different life cycle and does **not** involve cercariae

Q: Flame cells are primarily associated with which of the following organisms?

Trematodes. ***Correct: Trematodes*** - **Flame cells** are specialized **excretory/osmoregulatory structures** found in **Platyhelminthes (flatworms)**, which include **Trematodes** (flukes) and Cestodes (tapeworms). - These cells have a **tuft of cilia** that beat in a flickering motion (resembling a flame), driving fluid through tubules for waste removal and osmoregulation. - **Trematodes** are the most appropriate answer among the given options as they are medically important flatworms with flame cells. *Incorrect: Protozoa* - Protozoa are **single-celled organisms** that use **contractile vacuoles** for osmoregulation, not flame cells. - Examples include Entamoeba, Giardia, and Plasmodium species. *Incorrect: Nematodes* - **Nematodes** (roundworms) belong to phylum Nematoda and possess a distinct excretory system with **renette cells** or **H-shaped/tubular excretory canals**, not flame cells. - Examples include Ascaris, Enterobius, and hookworms. *Incorrect: None of the options* - This is incorrect because **Trematodes** do possess flame cells and is the correct answer among the choices provided.

Q: Which of the following is a primary cell line?

Chick embryo fibroblasts. ***Chick embryo fibroblasts*** - Primary cell lines are directly derived from **tissues** and have a limited lifespan in culture before undergoing senescence. - **Chick embryo fibroblasts** are isolated directly from chick embryos and propagated for a limited number of passages, making them a true primary cell culture. *Hela cells* - HeLa cells are a well-known example of a **continuous cell line**, meaning they can be cultured indefinitely. - They were originally derived from a cervical cancer patient and are considered **immortalized**. *Vero cells* - Vero cells are an **immortalized cell line** derived from the kidney of an African green monkey. - They are used extensively in virology and vaccine production due to their ability to be propagated for many passages. *WI-38* - WI-38 is a **diploid human cell strain** derived from lung tissue. - While they have a finite lifespan similar to primary cells, they represent a **cell strain** that has been subcultured and characterized, with more homogeneous growth characteristics than fresh primary cultures.

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 is an enveloped virus?

Dengue virus. ***Dengue virus*** - The **Dengue virus** is a member of the **Flaviviridae** family, which are known to be **enveloped viruses**. - Its outer lipid envelope, derived from the host cell, is crucial for its entry into host cells and evading the immune system. *Norwalk virus* - The **Norwalk virus**, also known as **Norovirus**, is a **non-enveloped RNA virus** belonging to the **Caliciviridae** family. - Its lack of an envelope makes it more resistant to disinfectants and environmental stresses, contributing to its high infectivity and ability to cause outbreaks of gastroenteritis. *Hep A virus* - **Hepatitis A virus (HAV)** is a **non-enveloped RNA virus** of the **Picornaviridae** family. - Its non-enveloped nature contributes to its stability in the environment and resistance to gastric acid, facilitating its fecal-oral transmission. *Adenovirus* - **Adenoviruses** are **non-enveloped DNA viruses** known for causing a variety of clinical manifestations, including respiratory infections, conjunctivitis, and gastroenteritis. - Their lack of an outer lipid envelope helps them survive in harsh environmental conditions and makes them highly stable.

Q: Which of the following statements about p24 is false?

Cannot be detected after seroconversion. ***Cannot be detected after seroconversion*** - This statement is **FALSE** and is the correct answer to this question. - **p24 antigen levels do decrease** after seroconversion due to immune complex formation with antibodies, but p24 can still be detected using modern assays. - In **advanced HIV disease** with declining CD4 counts, p24 antigen often becomes detectable again due to high viral loads. - Fourth-generation HIV tests detect both antibodies and p24 antigen throughout the infection course. *Cannot be seen in the first week* - This statement is **TRUE** (not the answer). - p24 antigen typically appears around **10-14 days** (1.5-2 weeks) after infection, which is after the first week (days 1-7). - The eclipse period (first 7-10 days) precedes p24 detection. *Can be detected after 3 weeks of infection* - This statement is **TRUE** (not the answer). - p24 antigen is consistently detectable at 3 weeks post-infection during the acute viremic phase. - Peak p24 levels occur around **2-4 weeks** after infection. *All of the above* - This is a distractor option and is incorrect since only one statement is false.

Q: Which of the following statements about Mycoplasma is correct?

Mycoplasma pneumoniae can cause lung infections.. ***Mycoplasma pneumoniae can cause lung infections.*** - **_Mycoplasma pneumoniae_** is a well-known cause of **atypical pneumonia**, often referred to as "walking pneumonia." - It infects the respiratory tract, leading to symptoms like **cough**, **fever**, and **sore throat**. - It is one of the most common causes of community-acquired pneumonia, especially in young adults and children. *Penicillin is effective against Mycoplasma.* - **Penicillin** and other beta-lactam antibiotics target bacterial **cell wall synthesis**. - **_Mycoplasma_** species inherently **lack a cell wall**, rendering these antibiotics ineffective. - Treatment requires antibiotics that target other mechanisms like protein synthesis (macrolides, tetracyclines). *Mycoplasma has a thick cell wall.* - **_Mycoplasma_** species are unique among bacteria because they **completely lack a cell wall**, making them pleomorphic (variable in shape). - This absence of a cell wall is a key characteristic that distinguishes them from most other bacteria. - The lack of cell wall makes them resistant to beta-lactam antibiotics and allows them to pass through bacterial filters. *Mycoplasma can be easily cultured on standard blood agar.* - **_Mycoplasma_** species are extremely **fastidious organisms** that require **specialized culture media** such as PPLO (pleuropneumonia-like organism) agar enriched with serum and yeast extract. - They cannot grow on standard blood agar or routine bacterial culture media. - Colonies are very small ("fried egg" appearance) and may take **1-3 weeks** to grow, making culture challenging.

Question 1

Which type of vaccine is used for chicken pox?

Accepted Answer

Live vaccine

Answer

Killed vaccine

Answer

Conjugated vaccine

Answer

Toxoid vaccine

Question 2

Which of the following statements is false regarding yersiniosis?

Accepted Answer

Caused by Yersinia pestis

Answer

Gram-negative bacillus

Answer

Caused by Yersinia pseudotuberculosis

Answer

Caused by Yersinia enterocolitica

Question 3

Which part of bacteria is most antigenic?

Accepted Answer

Lipopolysaccharide

Answer

Lipids

Answer

Nucleic acid

Answer

Protein coat

Question 4

Cercariae are the infective form of which of the following parasites?

Accepted Answer

Schistosoma hematobium

Answer

Paragonimus westermani

Answer

Fasciola hepatica

Answer

Taenia solium

Question 5

Flame cells are primarily associated with which of the following organisms?

Accepted Answer

Trematodes

Answer

Protozoa

Answer

Nematodes

Answer

None of the options

Question 6

Which of the following is a primary cell line?

Accepted Answer

Chick embryo fibroblasts

Answer

Hela cells

Answer

Vero cells

Answer

WI-38

Question 7

Virus quantification is done by-

Accepted Answer

Plaque assay

Answer

Studying virus-cell interactions

Answer

Visualizing virus particles

Answer

Virus isolation using eggs

Question 8

Which of the following is an enveloped virus?

Accepted Answer

Dengue virus

Answer

Norwalk virus

Answer

Hep A virus

Answer

Adenovirus

Question 9

Which of the following statements about p24 is false?

Accepted Answer

Cannot be detected after seroconversion

Answer

Cannot be seen in the first week

Answer

All of the above

Answer

Can be detected after 3 weeks of infection

Question 10

Which of the following statements about Mycoplasma is correct?

Accepted Answer

Mycoplasma pneumoniae can cause lung infections.

Answer

Penicillin is effective against Mycoplasma.

Answer

Mycoplasma has a thick cell wall.

Answer

Mycoplasma can be easily cultured on standard blood agar.

NEET-PG 2012 — Microbiology