Who discovered the malarial parasite?
Which of the following is an enrichment medium for cholera?
Which of the following statements is true regarding Diphyllobothrium?
Cercariae are the infective form of which of the following parasites?
Flame cells are primarily associated with which of the following organisms?
Which of the following is a primary cell line?
Virus quantification is done by-
Which of the following is an enveloped virus?
Which of the following statements about p24 is false?
Which part of bacteria is most antigenic?
NEET-PG 2012 - Microbiology NEET-PG Practice Questions and MCQs
Question 31: Who discovered the malarial parasite?
- A. Ronald Ross
- B. Paul Muller
- C. Charles Louis Alphonse Laveran (Correct Answer)
- D. Pampania
Explanation: ***Charles Louis Alphonse Laveran*** - **Charles Louis Alphonse Laveran** was a French physician who, in **1880**, observed parasites in the blood of a malaria patient. - He was awarded the **Nobel Prize in Physiology or Medicine in 1907** for his discovery of the role of protozoa in causing diseases, specifically recognizing the malarial parasite. *Ronald Ross* - **Ronald Ross** was a British physician who, in **1897**, demonstrated that **malaria is transmitted by mosquitoes**. - While he elucidated the **transmission cycle**, it was Laveran who first identified the parasite itself in human blood. - He received the **Nobel Prize in 1902** for this work. *Paul Muller* - **Paul Muller** was a Swiss chemist who was awarded the **Nobel Prize in Physiology or Medicine in 1948** for his discovery of the insecticidal properties of **DDT (dichlorodiphenyltrichloroethane)**. - His work was significant in combating insect-borne diseases like malaria, but he was not involved in the discovery of the malarial parasite. *Pampania* - This name does not correspond to any recognized figure in the discovery of the malarial parasite or its transmission. - This is a distractor option in the original examination question.
Question 32: Which of the following is an enrichment medium for cholera?
- A. TCBS medium
- B. Cary-Blair medium
- C. Alkaline peptone water (Correct Answer)
- D. MacConkey agar
Explanation: ***Alkaline peptone water*** - This is a commonly used **enrichment broth** for *Vibrio cholerae* due to its **high pH (around 8.6)**, which selectively suppresses the growth of most other intestinal flora. - The alkaline environment provides a favorable condition for the rapid multiplication of *Vibrio cholerae* before subculturing onto selective media. *TCBS medium* - **Thiosulfate citrate bile salts sucrose (TCBS) agar** is a **selective and differential medium** used for the isolation of *Vibrio cholerae*, not an enrichment medium. - It differentiates *Vibrio cholerae* (yellow colonies) from most other *Vibrio* species (blue-green colonies) and inhibits the growth of most non-Vibrio bacteria. *Cary-Blair medium* - This is a **transport medium** designed to maintain the viability of enteric bacterial pathogens, including *Vibrio cholerae*, for extended periods at ambient temperatures. - It prevents overgrowth of commensals and helps preserve the pathogen's concentration, but it does not promote growth. *MacConkey agar* - **MacConkey agar** is a **selective and differential medium** primarily used for the isolation and differentiation of gram-negative enteric bacilli. - It is not specifically designed for *Vibrio cholerae* and its selective properties (bile salts and crystal violet) and differential properties (lactose fermentation) are less optimal for *Vibrio* isolation compared to specialized media.
Question 33: Which of the following statements is true regarding Diphyllobothrium?
- A. Humans are the only definitive host
- B. Vitamin B12 deficiency always occurs in infection
- C. Fish are definitive hosts
- D. The operculated egg is a diagnostic feature (Correct Answer)
Explanation: ***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.
Question 34: Cercariae are the infective form of which of the following parasites?
- A. Schistosoma hematobium (Correct Answer)
- B. Paragonimus westermani
- C. Fasciola hepatica
- D. Taenia solium
Explanation: ***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
Question 35: Flame cells are primarily associated with which of the following organisms?
- A. Protozoa
- B. Nematodes
- C. Trematodes (Correct Answer)
- D. None of the options
Explanation: ***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.
Question 36: Which of the following is a primary cell line?
- A. Chick embryo fibroblasts (Correct Answer)
- B. Hela cells
- C. Vero cells
- D. WI-38
Explanation: ***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.
Question 37: Virus quantification is done by-
- A. Plaque assay (Correct Answer)
- B. Studying virus-cell interactions
- C. Visualizing virus particles
- D. Virus isolation using eggs
Explanation: ***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.
Question 38: Which of the following is an enveloped virus?
- A. Dengue virus (Correct Answer)
- B. Norwalk virus
- C. Hep A virus
- D. Adenovirus
Explanation: ***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.
Question 39: Which of the following statements about p24 is false?
- A. Cannot be detected after seroconversion (Correct Answer)
- B. Cannot be seen in the first week
- C. All of the above
- D. Can be detected after 3 weeks of infection
Explanation: ***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.
Question 40: Which part of bacteria is most antigenic?
- A. Lipopolysaccharide (Correct Answer)
- B. Lipids
- C. Nucleic acid
- D. Protein coat
Explanation: ***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