Allergy to penicillin is an example of:

Correct Answer: A

Rationale: Step-by-step rationale for choice A being correct: 1. Penicillin allergy involves IgE antibodies binding to penicillin. 2. This triggers mast cell degranulation, releasing histamine. 3. Histamine causes allergic symptoms like rash, swelling. 4. This immune response characterizes Type I hypersensitivity reactions. Summary of other choices: B: Type II reactions involve antibody-mediated cell destruction, not seen in penicillin allergy. C: Type III reactions involve immune complex deposition, not typical in penicillin allergy. D: Type IV reactions are delayed hypersensitivity reactions, not immediate like penicillin allergy.

Correct Answer: B

Rationale: The correct answer is B: All are correct. Candida albicans can cause skin infections such as candidiasis. Staphylococcus aureus and Streptococcus pyogenes are common bacteria that can also cause skin infections. Therefore, choice B is correct as all three microorganisms listed can cause skin infections. Choices A, C, and D are incorrect because individually, each of the microorganisms listed can cause skin infections.

Correct Answer: D

Rationale: The correct answer is D, "None of the above," because viruses like Parotitidis (mumps), Rubella, and Influenza A are not typically associated with reactivation under immunosuppressive therapy. Reactivation is more commonly seen in latent viruses like herpesviruses (e.g., herpes simplex, varicella-zoster), cytomegalovirus, and Epstein-Barr virus. These viruses can remain dormant in the body and reactivate when the immune system is compromised. Therefore, the correct answer is D, as the viruses mentioned in choices A, B, and C do not fit the criteria for reactivation under immunosuppressive therapy.

Correct Answer: D

Rationale: The correct answer is D because smallpox vaccination provides long-lasting immunity, often for a lifetime. Revaccination is not necessary as the initial vaccine confers sufficient protection. Choice A is incorrect because yearly revaccination is unnecessary and excessive. Choice B and C are also incorrect as there is no need for revaccination every second or third year. The key is to understand that smallpox vaccination typically provides lifelong immunity, making ongoing revaccination unnecessary.

Correct Answer: C

Rationale: The correct answer is C because plasmids do not encode essential bacterial properties. They are non-essential, extra-chromosomal DNA molecules that can replicate independently within bacterial cells. Plasmids mainly contain genes for antibiotic resistance, genetic transfer, and other specific functions. Choice A is correct as many plasmids do carry antibiotic resistance genes. Choice B is also accurate as plasmids are indeed smaller, circular, and exist outside the bacterial chromosome. Choice D is true as plasmids can facilitate bacterial conjugation, allowing the transfer of genetic material between bacteria.