Regarding fungal cell wall, all are true except:
Binding of gp120 causes:
What type of test is the Paul-Bunnell reaction?
Which antibody is elevated in parasitic infections?
Which of the following is a member of the kingdom Protista?
Katayama fever is caused by which of the following?
Necrotizing fasciitis is caused by -
The gene encoding cholera toxin is carried on -
Unsegmented eggs are in which parasite?
Which of the following substances is toxic to parasites?
NEET-PG 2012 - Microbiology NEET-PG Practice Questions and MCQs
Question 11: Regarding fungal cell wall, all are true except:
- A. Contains chitin
- B. Prevent osmotic damage
- C. Does not contain peptidoglycan
- D. Azoles act on them (Correct Answer)
Explanation: ***Azoles act on them*** - **Azole antifungals** primarily target the **ergosterol synthesis** pathway, specifically inhibiting the **lanosterol 14-alpha-demethylase** enzyme, which is located in the fungal cell membrane, not the cell wall. - While the cell wall is crucial for fungal viability, agents targeting it (e.g., **echinocandins**) are distinct from azoles. *Contains chitin* - The fungal cell wall is indeed a complex structure composed of various carbohydrates, with **chitin** being a major structural polysaccharide that provides rigidity. - Chitin is a **beta-(1,4)-linked polymer of N-acetylglucosamine** and is a unique component distinguishing fungal cells from animal cells. *Prevent osmotic damage* - The rigid fungal cell wall provides structural support and protects the cell from **environmental stresses**, particularly **osmotic lysis** in hypotonic environments. - It maintains the cell's integrity against internal **turgor pressure**, which is essential for fungal growth and survival. *Does not contain peptidoglycan* - Fungal cell walls are distinct from bacterial cell walls in their composition; they **do not contain peptidoglycan**. - **Peptidoglycan** is a characteristic component of bacterial cell walls, which is targeted by antibiotics like penicillins.
Question 12: Binding of gp120 causes:
- A. Infection of target cell
- B. Facilitation of co-receptor binding (Correct Answer)
- C. Fusing of virus and target cell
- D. None of the options
Explanation: ***Facilitation of co-receptor*** - **gp120** binding to the **CD4 receptor** on target cells induces a conformational change in gp120, which then exposes or creates a binding site for a **chemokine co-receptor** (CCR5 or CXCR4). - This interaction is crucial for the subsequent steps of viral entry, as it allows the virus to make further contact with the cell surface. *Infection of target cell* - While binding of gp120 is the *first step* in infection, it does not directly cause the infection itself. - Infection occurs after a series of events including co-receptor binding, membrane fusion, and reverse transcription. *Fusing of virus and target cell* - **Fusion** of the viral and cellular membranes is primarily mediated by **gp41**, which is part of the gp160 envelope glycoprotein complex alongside gp120. - This fusion event *follows* the binding of gp120 to CD4 and the co-receptor, as gp120 binding initiates the conformational changes that expose and activate gp41. *None of the options* - One of the provided options accurately describes a direct consequence of gp120 binding, making this option incorrect.
Question 13: What type of test is the Paul-Bunnell reaction?
- A. Agglutination (Correct Answer)
- B. CF
- C. Precipitation
- D. Flocculation test
Explanation: ***Agglutination*** - The **Paul-Bunnell reaction** is an **agglutination test** used to detect specific antibodies in infectious mononucleosis. - It identifies **heterophile antibodies** that agglutinate **sheep red blood cells**. *CF* - **Complement Fixation (CF) tests** measure antibody or antigen by observing the *fixation* of complement components. - This method is distinct from the **direct clumping** of cells seen in agglutination. *Precipitation* - **Precipitation reactions** involve soluble antigens and antibodies forming an **insoluble lattice** that settles out of solution. - These reactions detect soluble complexes, not the clumping of cells. *Flocculation test* - **Flocculation tests** are a type of **precipitation reaction** where *finely dispersed particles* form visible clumps (floccules). - While related to precipitation, the Paul-Bunnell reaction specifically involves the *agglutination of red blood cells*.
Question 14: Which antibody is elevated in parasitic infections?
- A. IgA
- B. IgE (Correct Answer)
- C. IgG
- D. IgM
Explanation: **Correct: IgE** - **IgE** is centrally involved in the immune response to **parasitic infections**, particularly helminths. - This antibody promotes the release of inflammatory mediators from **mast cells** and **basophils**, leading to the expulsion of parasites. - Elevated IgE is a **characteristic finding** in helminthic infections and is used diagnostically. *Incorrect: IgA* - **IgA** is primarily found in **mucosal secretions** and plays a key role in protecting against pathogens at mucosal surfaces. - While it has a role in general immunity, it is **not the primary antibody** involved in the systemic response to parasitic infections. *Incorrect: IgG* - **IgG** is the most abundant antibody in serum and provides **long-term immunity** against many pathogens. - While IgG levels may rise in response to chronic parasitic infections, it is **not the characteristic or primary antibody** elevated in active or initial parasitic responses. *Incorrect: IgM* - **IgM** is the first antibody produced during a **primary immune response** and is important for activating the complement system. - While it indicates an early infection, it is **less specific** for parasitic infections compared to IgE.
Question 15: Which of the following is a member of the kingdom Protista?
- A. Fungi
- B. Protozoa (Correct Answer)
- C. Bacteria
- D. Virus
Explanation: ***Protozoa*** - **Protozoa** are single-celled eukaryotic organisms that are heterotrophic and typically motile, fitting the classification within the kingdom Protista. - Protista is a **diverse kingdom** encompassing various eukaryotic organisms that are not animals, plants, or fungi, and protozoa represent the animal-like protists. - Examples include **Amoeba, Plasmodium, Giardia**, and Entamoeba. *Virus* - **Viruses** are not classified within any kingdom as they are **acellular** (not made of cells). - They are obligate intracellular parasites that require a host cell to replicate. - Lack cellular machinery and metabolic processes that define living organisms. *Fungi* - **Fungi** belong to their own distinct kingdom, Fungi, and are not classified under Protista. - They are **heterotrophic eukaryotes** that absorb nutrients and have cell walls made of chitin. - Examples include yeasts, molds, and mushrooms. *Bacteria* - **Bacteria** are prokaryotic organisms, meaning they lack a membrane-bound nucleus and other membrane-bound organelles. - They belong to the kingdom **Monera** (or domain Bacteria in modern classification), separate from eukaryotic kingdoms like Protista. - They have peptidoglycan cell walls and reproduce by binary fission.
Question 16: Katayama fever is caused by which of the following?
- A. F. hepatica
- B. C. sinensis
- C. A. lumbricoides
- D. S. japonicum (Correct Answer)
Explanation: ***Correct: S. japonicum*** - Katayama fever, also known as **acute schistosomiasis**, is a systemic hypersensitivity reaction to the migrating schistosomula and oviposition of eggs that primarily occurs in infections with **_Schistosoma japonicum_** or _S. mansoni_. - It presents with fever, chills, cough, diarrhea, abdominal pain, hepatosplenomegaly, and eosinophilia, typically 2-8 weeks after exposure to contaminated water. - S. japonicum tends to cause the most severe form of Katayama fever. *Incorrect: F. hepatica* - **_Fasciola hepatica_** causes fascioliasis, an infection of the bile ducts and liver, which can present with fever and eosinophilia, but it does not typically cause the acute systemic reaction known as Katayama fever. - The disease is usually acquired by ingesting **metacercariae** on aquatic vegetation or in contaminated water. *Incorrect: C. sinensis* - **_Clonorchis sinensis_** is the Chinese liver fluke, causing clonorchiasis, an infection primarily of the bile ducts. - Symptoms are often mild or asymptomatic but can include abdominal pain, indigestion, diarrhea, and jaundice in heavy infections, without the distinct acute systemic syndrome of Katayama fever. *Incorrect: A. lumbricoides* - **_Ascaris lumbricoides_** is a roundworm that causes ascariasis, primarily affecting the gastrointestinal tract. - While it can cause pulmonary symptoms during larval migration (Löffler's syndrome), it does not cause Katayama fever, which is specific to schistosomiasis.
Question 17: Necrotizing fasciitis is caused by -
- A. Beta hemolytic streptococci (Correct Answer)
- B. Pneumococcus
- C. Staphylococcus aureus
- D. Clostridium perfringens
Explanation: ***Beta hemolytic streptococci*** - **Group A Streptococcus (GAS)**, specifically *Streptococcus pyogenes*, is the most common cause of **Type II necrotizing fasciitis**. - Its virulence factors, like **exotoxins**, contribute to rapid tissue destruction and systemic toxicity. *Staphylococcus aureus* - While *S. aureus* can cause severe skin and soft tissue infections, it is more commonly associated with **cellulitis**, **abscesses**, and **septic arthritis**. - It can be a co-pathogen in **polymicrobial (Type I) necrotizing fasciitis** but is less frequent as a sole cause compared to GAS for Type II. *Pneumococcus* - *Streptococcus pneumoniae* (Pneumococcus) is primarily known for causing respiratory infections like **pneumonia**, **otitis media**, and **meningitis**. - It is not a typical causative agent of necrotizing fasciitis. *Clostridium perfringens* - This bacterium is the primary cause of **gas gangrene** (clostridial myonecrosis), a severe form of necrotizing soft tissue infection involving muscle tissue. - While also a flesh-eating bacterium, its clinical presentation and typical affected tissues differ from those of necrotizing fasciitis caused by streptococci.
Question 18: The gene encoding cholera toxin is carried on -
- A. Chromosomal DNA
- B. Extrachromosomal plasmid
- C. Bacteriophage (Correct Answer)
- D. Transposon
Explanation: ***Bacteriophage*** - The gene encoding **cholera toxin (ctxA and ctxB)** is carried on the genome of a **lysogenic bacteriophage** known as CTXf. - This phage integrates its DNA into the *Vibrio cholerae* chromosome, allowing for toxin production. *Chromosomal DNA* - While the **phage DNA (containing the cholera toxin gene)** integrates into the *Vibrio cholerae* chromosome, the toxin itself is **not directly encoded by the core bacterial chromosomal DNA** but by the integrated phage DNA. - Many bacterial virulence factors are encoded on the main chromosome, but cholera toxin is a specific exception. *Extrachromosomal plasmid* - **Plasmids** are extrachromosomal DNA molecules that can carry virulence genes, but the cholera toxin gene is **not typically found on a plasmid** in *Vibrio cholerae*. - Examples of plasmid-encoded toxins include some enterotoxins in *E. coli*. *Transposon* - **Transposons** are "jumping genes" that can move within and between DNA molecules, but they are generally **mobile genetic elements** that carry genes, not the direct source of the cholera toxin gene. - While transposons can sometimes contribute to the movement of virulence genes, the cholera toxin gene specifically originates from a bacteriophage.
Question 19: Unsegmented eggs are in which parasite?
- A. Ancylostoma
- B. Necator americanus
- C. Dracunculus
- D. Trichuris trichiura (Correct Answer)
Explanation: ***Trichuris trichiura*** - *Trichuris trichiura* (whipworm) eggs are typically **unembryonated** or **unsegmented** when passed in feces. - Upon defecation, the eggs require a period of **development in soil** to become infective. *Ancylostoma* - **Hookworm (Ancylostoma)** eggs are typically **segmented** (possessing a 2-8 cell stage) when passed in feces. - They develop into **rhabditiform larvae** in the soil. *Necator americanus* - **Hookworm (Necator americanus)** eggs are also typically **segmented** (possessing a 2-8 cell stage) when passed in feces. - Like *Ancylostoma*, they require further development in soil to become infective. *Dracunculus* - *Dracunculus medinensis* (Guinea worm) does not lay eggs; instead, it releases **larvae** from the skin blister of the host into water. - The larvae are then ingested by **cyclops** (copepods) to continue their life cycle.
Question 20: Which of the following substances is toxic to parasites?
- A. Peroxidase (Correct Answer)
- B. Interferon-alpha
- C. IL-2 (Interleukin-2)
- D. IL-6 (Interleukin-6)
Explanation: ***Peroxidase*** - **Peroxidase** enzymes, especially those produced by **eosinophils**, generate toxic oxygen metabolites and hypohalous acids that are highly effective at damaging and killing parasites. - This enzyme plays a crucial role in the host's defense against larger parasites, such as **helminths (worms)**. *Interferon-alpha* - **Interferon-alpha** is an important cytokine primarily known for its **antiviral effects** and its role in activating natural killer (NK) cells. - While it modulates immune responses, it does not directly act as a toxic substance to parasites. *IL-2 (Interleukin-2)* - **IL-2** is a growth factor that primarily promotes the **proliferation and differentiation of T cells**, enhancing adaptive immune responses. - It does not directly kill parasites but rather supports the immune cells involved in parasite clearance. *IL-6 (Interleukin-6)* - **IL-6** is a pleiotropic cytokine involved in **inflammation, acute phase responses**, and the differentiation of B cells and T cells. - While it contributes to overall immune regulation, it lacks direct parasiticidal activity.