A patient presents with a history of diarrhea of several weeks' duration. Which of the following may be the cause?

Correct Answer: B

Rationale: The correct answer is B: Yersinia enterocolitica. Y. enterocolitica is known to cause gastroenteritis and diarrhea in humans. It is often associated with contaminated food or water. Bordetella pertussis causes whooping cough, not diarrhea. Corynebacterium diphtheria causes respiratory diphtheria. Neisseria meningitidis is associated with meningitis and septicemia, not diarrhea. Therefore, based on the patient's symptoms and history, Y. enterocolitica is the most likely cause of the diarrhea in this case.

Correct Answer: A

Rationale: The correct answer is A because lipophilization is the process of removing water from cells under deep vacuum in a frozen state. Dehydration of the cell at a low temperature helps to preserve the cellular structure and components. Choice B is incorrect as hydration does the opposite of what lipophilization aims to achieve. Choice C is incorrect as lipophilization does not involve enriching cells with proteins. Choice D is incorrect as lipophilization does not involve removing protein content from cells.

Correct Answer: A

Rationale: The correct answer is A: Air. In transmissive infections, the vector refers to the means by which the infectious agent is transmitted from one host to another. Air can carry pathogens such as viruses and bacteria, leading to respiratory infections like the flu or tuberculosis. Airborne transmission occurs when droplets containing the pathogens are inhaled. Objects (B), medical devices (C), and water (D) can also transmit infections, but they are not specifically related to transmissive infections. Objects and medical devices can harbor pathogens, while waterborne infections are transmitted through contaminated water sources. However, in the context of transmissive infections, the primary vector is the air due to its ability to carry infectious agents over distances.

Correct Answer: C

Rationale: Step 1: Chlorhexidine belongs to the group of biguanides, which are commonly used for disinfecting hands, skin, and mucous membranes. Step 2: It is known to have broad-spectrum antimicrobial activity against various pathogens. Step 3: The usage of chlorhexidine in healthcare settings for preoperative skin preparation and surgical hand scrub is well-established. Step 4: The effectiveness and safety profile of chlorhexidine make it a preferred choice for disinfection purposes. Summary: - Option A is incorrect as chlorhexidine is not characterized by strong human toxicity. - Option B is incorrect as chlorhexidine is not classified as an alcohol and is primarily used for disinfecting hands, skin, and mucous membranes. - Option D is incorrect as chlorhexidine has a wide range of applications in disinfection, especially in healthcare settings.

Correct Answer: D

Rationale: The correct answer is D, as all options A, B, and C are determinants of antigenicity. A: Chemical nature influences how the immune system recognizes antigens. B: The size of the antigen affects its ability to be recognized by immune cells. C: Antigens of foreign origin are more likely to trigger an immune response. Therefore, all of these factors together play a crucial role in determining antigenicity.