A child cut his leg with a piece of glass while playing and was brought to the clinic for the injection of tetanus toxoid. In order to prevent the development of anaphylactic shock the serum was administered by Bezredka method. What mechanism underlies this method of desensitization of the body?

Correct Answer: A

Rationale: The correct answer is A: Binding of IgE fixed to the mast cells. The Bezredka method involves injecting small, gradually increasing doses of the antigen (tetanus toxoid) to desensitize the body and prevent anaphylactic shock. This process works by binding the IgE antibodies fixed to mast cells, thereby reducing the release of allergic mediators like histamine. This prevents the cascade of events that lead to anaphylactic shock. Choice B (Blocking the mediator synthesis in the mast cells) is incorrect because the Bezredka method does not block mediator synthesis but rather prevents the release of mediators by binding IgE. Choice C (Stimulation of immune tolerance to the antigen) is incorrect as the Bezredka method does not primarily focus on inducing immune tolerance but rather on preventing anaphylactic reactions. Choice D (Stimulation of the synthesis of antigen-specific IgG) is incorrect because the Bezredka method targets IgE antibodies on mast cells

Correct Answer: D

Rationale: The correct answer is D: iatrogenic infections. Iatrogenic infections refer to infections caused by medical or surgical treatment, including procedures that introduce microorganisms into the body. In this case, infections of the reproductive tract caused by medical procedures fall under this category. A: Chronic infections do not specifically refer to infections caused by medical procedures. B: Endogenous infections arise from organisms already present in or on the body, not introduced through medical procedures. C: Systemic infections affect the entire body, not specific to infections caused by medical procedures. Therefore, the term "iatrogenic infections" is the most appropriate choice in this context.

Correct Answer: A

Rationale: The correct answer is A: Balantidium coli. This large ciliated protozoa with a kidney-shaped macronucleus is characteristic of Balantidium coli, an intestinal parasite known to cause foul-smelling diarrhea in humans. Balantidium coli is the only option among the choices that fits this specific description. Entamoeba histolytica causes amoebic dysentery, Giardia lamblia causes giardiasis, and Trichomonas hominis is a non-pathogenic protozoa found in the intestinal tract. Therefore, based on the morphology described in the question, Balantidium coli is the correct causative agent.

Correct Answer: B

Rationale: The correct answer is B: Shigellosis. Shigellosis is caused by the bacteria Shigella, commonly transmitted through contaminated food and water. The bacteria can spread easily in unsanitary conditions. Mumps (A) is a viral infection spread through respiratory droplets. Legionellosis (C) is caused by the Legionella bacteria found in water sources like cooling towers. Tuberculosis (D) is a bacterial infection transmitted through the air. Therefore, the correct answer is B as it directly relates to contaminated food transmission.

Correct Answer: A

Rationale: The correct answer is A: Clostridia. Fusiform spore-forming microorganisms that stain violet-blue with Gram's stain are characteristic of Clostridia. Clostridia are anaerobic, rod-shaped bacteria known for their ability to form spores and cause diseases such as tetanus and botulism. Summary of other choices: B: Streptococci are spherical, not fusiform, and typically do not form spores. C: Spirochaete are spiral-shaped bacteria and do not typically form spores. D: Actinomycete are filamentous bacteria that do not typically form spores and do not stain violet-blue with Gram's stain.