In which of the following GIT infections, the bacteria adhere to the intestine wall and produce toxins:

Correct Answer: B

Rationale: Rationale: 1. Enteropathogenic E.coli (EPEC) adheres to the intestinal wall using bundle-forming pili. 2. EPEC produces toxins that disrupt cell structure and function, leading to diarrhea. 3. Shigella spp. invade intestinal cells, Salmonella spp. invade and multiply within cells, and Vibrio cholerae produces cholera toxin causing profuse watery diarrhea. Summary: A, C, and D choices are incorrect because they do not specifically adhere to the intestine wall and produce toxins like EPEC does.

Correct Answer: D

Rationale: The correct answer is D: IgM. IgM antibodies are the first type of antibodies produced by the immune system in response to an acute infection, such as Parvovirus B19. During the first 10-14 days of the infection, IgM antibodies are usually detectable in the blood, indicating a recent or ongoing infection. IgG antibodies (choice A) are produced later in the immune response and indicate past infection or immunity. IgA (choice B) is more commonly associated with mucosal immunity and may not be as prominent in the early stages of systemic infections. IgD (choice C) is primarily found on the surface of B cells and is involved in B cell activation but is not typically used as a marker for acute infections like IgM.

Correct Answer: D

Rationale: The correct answer is D: All of the above. The cytoplasmic membrane of prokaryotes consists of phospholipids which form a lipid bilayer, providing structure and selective permeability. Proteins are embedded in this membrane, serving various functions like transport and signaling. Carbohydrates may also be present on the surface for cell recognition. Therefore, all three components (phospholipids, proteins, and carbohydrates) are essential parts of the prokaryotic cytoplasmic membrane. Option A, B, and C individually do not fully encapsulate the complexity and composition of the prokaryotic cytoplasmic membrane.

Correct Answer: A

Rationale: The correct answer is A: Β-lactamase. In ELISA, enzymes like alkaline phosphatase, horseradish peroxidase, and Β-galactosidase are commonly used as labels to detect the presence of specific molecules. Β-lactamase is not typically used in ELISA as it is an enzyme used to hydrolyze β-lactam antibiotics. Therefore, it does not serve the purpose of detecting specific molecules in ELISA. Alkaline phosphatase, horseradish peroxidase, and Β-galactosidase are preferred enzymes in ELISA due to their ability to produce a detectable signal when bound to specific molecules.

Correct Answer: C

Rationale: The pertussis toxin inhibits the adenylate cyclase-mediated conversion of ATP to cyclic AMP, leading to decreased levels of cyclic AMP in the cell. This disrupts important cellular signaling pathways, affecting immune response and causing symptoms of pertussis. Choices A, B, and D are incorrect because the pertussis toxin does not directly affect protein synthesis, provoke overproduction of mucus in tracheal cells, or provoke release of electrolytes.