A 4 year old child had Mantoux test. 60 hours after tuberculin introduction a focal skin hardening and redness 15 mm in diameter appeared. It was regarded as positive test. What type of hypersensitivity reaction is this test based upon?

Correct Answer: A

Rationale: The correct answer is A: Delayed-type hypersensitivity. The Mantoux test is a type IV hypersensitivity reaction, which is also known as delayed-type hypersensitivity. This reaction typically occurs 48-72 hours after exposure to an antigen, such as tuberculin in this case. The focal skin hardening and redness that appeared 60 hours after tuberculin introduction align with the timeline and characteristics of a delayed-type hypersensitivity reaction. Summary: - Choice A (Delayed-type hypersensitivity): Correct, as explained above. - Choice B (Immune complex-mediated hypersensitivity): Incorrect, as this reaction involves immune complexes and typically presents with tissue damage and inflammation. - Choice C (Complement-mediated cytotoxic hypersensitivity): Incorrect, as this reaction involves the activation of complement proteins leading to cell lysis. - Choice D (Immediate hypersensitivity): Incorrect, as this reaction, such as in allergies, occurs within minutes to hours of exposure to an antigen and involves IgE-mediated mast

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: B

Rationale: The correct answer is B: Absence of hemagglutination. In the reaction inhibition of hemagglutination, specific antibodies bind to antigens on red blood cells, preventing their agglutination. This results in the absence of visible clumping of red blood cells, which is known as hemagglutination. Therefore, the presence of specific antibodies is visualized by the absence of hemagglutination. Incorrect Choices: A: Absence of hemolysis - Hemolysis refers to the rupture of red blood cells, which is not relevant in the context of hemagglutination. C: Presence of hemagglutination - This is the opposite of what is expected when specific antibodies are present and inhibiting hemagglutination. D: Presence of hemolysis - Again, hemolysis is not directly related to the inhibition of hemagglutination by specific antibodies.

Correct Answer: D

Rationale: The correct answer is D (4) because biosafety levels range from 1 to 4, each corresponding to the level of containment required when handling different types of organisms. BSL-1 is for low-risk agents, while BSL-4 is for dangerous pathogens. Choice A (1) is incorrect as there are multiple levels, not just one. Choice B (2) and C (3) are incorrect as they do not account for all the levels of biosafety required for handling various organisms. Therefore, D is the correct answer as it encompasses the full range of biosafety levels.

Correct Answer: A

Rationale: The correct answer is A: incidence. Incidence refers to the number of new cases of a disease occurring within a specific time period in relation to the healthy population. It helps in understanding the risk of developing the disease. Prevalence (B) is the total number of existing cases at a given point in time. Virulence (C) is the severity of the disease once contracted. Mortality (D) refers to the number of deaths due to the disease, not the new cases. Therefore, the correct term for new cases is incidence.

Correct Answer: B

Rationale: Transduction is the transfer of genetic material between bacterial cells with the help of a phage (virus). This process involves a phage infecting a bacterial cell, replicating inside it, and then transferring bacterial DNA along with phage DNA to another bacterial cell. This is different from transformation (choice A) which involves the uptake of naked DNA by a bacterial cell and plasmid transfer (choice C) which involves the transfer of small, circular DNA molecules. Therefore, the correct answer is B because it specifically describes the process of transduction in bacteria, while choices A and C describe different mechanisms of genetic transfer.

Correct Answer: B

Rationale: The correct answer is B: Bergey's Manual of Systematic Bacteriology. This manual is a comprehensive and authoritative resource specifically dedicated to bacterial taxonomy, classification, and identification. It provides detailed descriptions and classification schemes for bacteria, aiding in accurate identification and understanding of bacterial species. Gray's Anatomy (choice A) focuses on human anatomy, the WHO Manual (choice C) focuses on global health guidelines, and Darwin's Origin of Species (choice D) discusses evolution and natural selection, none of which are specialized taxonomic resources for bacteria.

Correct Answer: B

Rationale: The correct answer is B: antitoxin. Antitoxin is the specific antidote to botulinum toxin as it helps neutralize the toxin in the body. Sodium bicarbonate (A) is used to treat acidosis, pralidoxime (C) is used for organophosphate poisoning, and naloxone (D) is used for opioid overdose. Antitoxin directly targets and counteracts the botulinum toxin, making it the appropriate antidote in cases of botulism.

Correct Answer: D

Rationale: The correct answer is D: sterols. Eukaryotic cytoplasmic membranes contain sterols, such as cholesterol, which provide stability and regulate fluidity. This is a key characteristic that distinguishes them from prokaryotic membranes. Cellulose (A) is a component of plant cell walls, not the cytoplasmic membrane. Starch (B) is a carbohydrate used for energy storage in plants. Chitin (C) is a component of fungal cell walls and arthropod exoskeletons, not found in eukaryotic cytoplasmic membranes.