A bacteriological laboratory tests canned meat for botulinum toxin. Extract of the tested material and ABE botulinum antitoxin serum was introduced into the test group of mice; a control group of mice received the extract without antibotulinic serum. What serological reaction was used?

Correct Answer: A

Rationale: The correct answer is A: Neutralization. In this experiment, the ABE botulinum antitoxin serum is introduced along with the extract to neutralize the botulinum toxin. This is a specific type of serological reaction where the antitoxin serum binds to and neutralizes the toxin, preventing it from causing harm. Summary: - B: Precipitation involves the formation of visible insoluble complexes, which is not the case in this experiment. - C: Complement binding involves the activation of complement proteins, which is not the main mechanism at play here. - D: Double immunodiffusion is a technique to detect the presence of specific antigens or antibodies, but it is not directly related to the neutralization of toxins as seen in this experiment.

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: Gram-positive rod-shaped bacterium. Campylobacter fetus is actually a Gram-negative bacterium. This is because it has a thin peptidoglycan layer in its cell wall, which does not retain the crystal violet stain used in the Gram-staining technique. It appears red or pink under a microscope after counterstaining with safranin. Therefore, statement A is incorrect. B: Optimal temperature for cultivation 35-37C - Correct, as Campylobacter fetus thrives at this temperature range. C: Opportunistic pathogen causes infections usually in newborns, immunocompromised patients, and cancer - Correct, as Campylobacter fetus can cause infections in these populations. D: Fastidious, microaerophile - Correct, as Campylobacter fetus is fastidious and requires specific growth conditions, including low oxygen levels.

Correct Answer: D

Rationale: The correct answer is D: rRNA. Bacterial ribosomes consist mainly of ribosomal RNA (rRNA), which plays a crucial role in protein synthesis. Ribosomes are composed of rRNA and proteins, with rRNA being the major component. rRNA serves as the structural and catalytic component of the ribosome, aiding in the binding of mRNA and tRNA during translation. Carbohydrates (A) and lipids (B) are not primary components of ribosomes, and DNA (C) is not found in ribosomes as they are involved in storing genetic information, not in protein synthesis.

Correct Answer: B

Rationale: The correct answer is B: mycorrhizae. Mycorrhizae are symbiotic fungi that form a mutualistic relationship with plant roots, aiding in the absorption of minerals and water. They enhance the plant's nutrient uptake capacity, promoting plant growth and health. Decomposers (A) break down dead organic matter, yeasts (C) are single-celled fungi used in fermentation, and molds (D) are fungi that grow in multicellular filaments. These options do not specifically assist plant roots in mineral and water absorption like mycorrhizae do.

Correct Answer: B

Rationale: The correct answer is B: Azotobacter species. Azotobacter are known for their ability to fix nitrogen through the process of nitrogen fixation, converting atmospheric nitrogen into a form that plants can use. Bacillus cereus is not known for nitrogen fixation. Clostridium botulinum is a bacterium that causes botulism and does not fix nitrogen. Escherichia coli is a common gut bacterium but does not have the ability to fix nitrogen. Thus, Azotobacter species is the correct choice based on its unique ability to fix nitrogen.

Correct Answer: D

Rationale: The correct answer is D because a fourfold increase in titer in the second serum sample indicates a significant rise in specific antibodies, which is crucial for diagnosing viral infections accurately. This increase is considered significant in serologic reactions as it shows a strong antibody response to the virus. A: A threshold increase may not be substantial enough to confirm a diagnostic antibody response. B: Dismissing the increase in titer would overlook important diagnostic information. C: A twofold increase may not be as indicative of a strong antibody response compared to a fourfold increase.

Correct Answer: A

Rationale: The correct answer is A: Facultative anaerobes. Facultative anaerobes can survive in both aerobic and anaerobic conditions because they have the metabolic flexibility to switch between utilizing oxygen for respiration in aerobic conditions and using fermentation in anaerobic conditions. Obligate aerobes (B) require oxygen for survival, obligate anaerobes (C) cannot survive in the presence of oxygen, and microaerophiles (D) require low levels of oxygen to grow effectively. Therefore, the ability of facultative anaerobes to adapt to varying oxygen levels makes them the correct choice for this question.

Correct Answer: A

Rationale: The correct answer is A: Type 1 hypersensitivity reaction. In this type of reaction, allergens trigger the production of IgE antibodies, leading to mast cell and basophil degranulation and release of inflammatory mediators like histamine. This causes immediate allergic symptoms. Seafood and eggs are common allergens that can elicit this response. B: Type 2 hypersensitivity reaction involves antibodies targeting cell surface or extracellular matrix antigens, leading to cell destruction or dysfunction. This is not the mechanism in seafood or egg allergies. C: Type 3 hypersensitivity reaction involves immune complex deposition in tissues, leading to inflammation and tissue damage. This is not the mechanism in seafood or egg allergies. D: Type 4 hypersensitivity reaction is cell-mediated and involves T cells causing inflammation and tissue damage. This is not the mechanism in seafood or egg allergies.