The specific binding of HIV to the CD4 surface molecules of the target cells is brought about by:

Correct Answer: A

Rationale: The correct answer is A: Gp120. Gp120 is a glycoprotein on the surface of the HIV virus that specifically binds to the CD4 receptor on target cells. This binding is essential for the virus to enter the host cell and initiate the infection process. Gp41 is another glycoprotein on the virus that helps with membrane fusion, not binding to CD4. Gp32 and Gp55 are not involved in the specific binding of HIV to CD4 molecules. So, A is correct as it directly plays a key role in the initial attachment of HIV to target cells.

Correct Answer: A

Rationale: The correct answer is A: Acid resistance. The Ziehl-Neelsen staining technique is specifically used to detect acid-fast bacteria like Mycobacterium tuberculosis, which is resistant to acid decolorization. This property allows the tuberculosis bacillus to retain the stain even after exposure to acid-alcohol, appearing red under the microscope. Explanation of incorrect choices: B: Alkali resistance - This property is not relevant in the context of Ziehl-Neelsen staining for acid-fast bacteria. C: Alcohol resistance - While alcohol resistance is related to acid-fastness, it is not the specific property highlighted by Ziehl-Neelsen staining. D: Capsule formation - Capsule formation is a different characteristic and not directly related to the staining behavior of acid-fast bacteria in the Ziehl-Neelsen technique.

Correct Answer: C

Rationale: Sterilization refers to the complete elimination of all microorganisms, including their spores, which are the most resistant form of microbial life. Spores have a tough outer coating that protects them from harsh conditions, making them more difficult to destroy compared to vegetative cells, viruses, and protozoa. Therefore, the correct answer is C because sterilization targets and eliminates all forms of microorganisms, including spores. Choices A, B, and D are incorrect because sterilization goes beyond just targeting vegetative cells, viruses, or protozoa; it aims to eliminate all microorganisms present.

Correct Answer: C

Rationale: Rationale: Both Clostridium botulinum and Clostridium tetani produce neurotoxins. Botulinum toxin affects the nervous system by blocking neurotransmitter release, causing paralysis. Tetanus toxin affects the nervous system by interfering with neurotransmitter release, leading to muscle stiffness and spasms. Therefore, Choice C is correct. Choices A and B alone are incorrect because they only mention one of the bacteria that produces a neurotoxin. Choice D is incorrect because both bacteria mentioned in Choices A and B produce neurotoxins.

Correct Answer: A

Rationale: The correct answer is A: Tetanus. Tetanus is caused by the bacterium Clostridium tetani, which produces a toxin affecting the nervous system. Symptoms such as malaise, irritability, muscular twitching, and high body temperature are characteristic of tetanus due to muscle spasms and rigidity. The 15-day incubation period after trauma aligns with the typical onset of tetanus symptoms. Incorrect choices: B: Anaerobic gas gangrene - This condition usually presents with localized tissue necrosis and gas bubbles in the affected area, not systemic symptoms like malaise and headache. C: Erysipelas - This is a bacterial skin infection presenting with red, swollen patches, not the neurological symptoms seen in tetanus. D: Acute thrombophlebitis - This is a blood clot in a vein causing pain and swelling, not associated with the systemic symptoms and muscle twitching seen in tetanus.

Correct Answer: A

Rationale: The correct answer is A: Staphylococcus aureus. 1. Gram-positive cocci in clusters suggest staphylococci. 2. Catalase-positive indicates staphylococci since streptococci are catalase-negative. 3. Coagulase-positive further confirms Staphylococcus aureus, distinguishing it from other staphylococci. Summary: B is incorrect as Streptococcus pyogenes is catalase-negative. C is incorrect as Micrococcus luteus is catalase-negative and coagulase-negative. D is incorrect as Enterococcus faecalis is catalase-negative and coagulase-negative.

Correct Answer: B

Rationale: The correct answer is B: prostatitis. Prostatitis is the most common bacterial infection affecting the male reproductive system. It is characterized by inflammation of the prostate gland due to bacterial infection. Symptoms include pain in the pelvic area, difficulty urinating, and fever. Cystitis (A) is a bladder infection, not specific to the male reproductive system. Mastitis (C) is inflammation of the breast tissue, which is not related to the male reproductive system. Nephritis (D) is inflammation of the kidneys, which is also not specific to the male reproductive system.

Correct Answer: A

Rationale: The correct answer is A: Actinomycosis. This is supported by the presence of purulent foci with druses consisting of short rod-like elements attached to a homogenous center, which is characteristic of Actinomyces species. Actinomycosis commonly presents with granulation tissue and connective tissue formation. B: Tuberculosis does not typically present with druses containing short rod-like elements. C: Syphilis does not typically present with purulent foci or druses. D: Candidosis does not typically present with the described features of purulent fluxing and druses with short rod-like elements.

Correct Answer: A

Rationale: The correct answer is A: Shigella dysenteriae. This bacteria produces the Shiga toxin, which inhibits protein synthesis by interfering with the ribosomes. Shigella dysenteriae causes severe gastrointestinal illness. The other choices, B: Clostridium botulinum, produces a neurotoxin that blocks neurotransmitter release. C: Streptococcus pneumoniae causes pneumonia and other respiratory infections. D: Mycobacterium tuberculosis causes tuberculosis by infecting the lungs. Thus, based on the toxin production and mode of action, Shigella dysenteriae is the correct answer.