Which of the following bacteria is responsible for producing a neurotoxin that causes tetanus?

Correct Answer: B

Rationale: The correct answer is B: Clostridium tetani. Clostridium tetani produces tetanospasmin, a neurotoxin causing tetanus. It enters the body through wounds and affects the nervous system. A: Clostridium botulinum produces botulinum toxin causing botulism, not tetanus. C: Streptococcus pneumoniae causes pneumonia, not tetanus. D: Mycobacterium tuberculosis causes tuberculosis, not tetanus.

Correct Answer: D

Rationale: The correct answer is D: Binary fission. Binary fission is a method of bacterial cell division, not a method of acquiring genetic material. Transformation, conjugation, and transduction are mechanisms through which bacteria can acquire genetic material from other sources. Transformation involves the uptake of naked DNA from the environment, conjugation is the transfer of genetic material through direct cell-to-cell contact, and transduction is the transfer of genetic material via bacteriophages. Therefore, binary fission is the only option that does not involve the acquisition of new genetic material.

Correct Answer: B

Rationale: The correct answer is B because antigenic drift is not caused by the exchange of genetic information between animal and human influenza viruses. Antigenic drift is actually due to point mutations in the genes that encode for the surface proteins of the virus, leading to small changes in the antigens. These mutations can affect the hemagglutinin of both type A and B influenza viruses, making choices A and C correct. Choice D is incorrect because antigenic drift can occur in both type A and B influenza viruses, with type B being less prone to drift compared to type A.

Correct Answer: A

Rationale: Step-by-step rationale: 1. Anopheles mosquitoes are the primary vectors for transmitting malaria. 2. They prefer stagnant water for breeding, common in tropical regions. 3. Culex mosquitoes primarily spread diseases like West Nile virus. 4. Aedes mosquitoes transmit diseases like Zika and dengue fever. 5. Mansonia mosquitoes are known for transmitting filarial diseases. Therefore, the correct answer is A (Anopheles), as they are specifically associated with spreading malaria.

Correct Answer: A

Rationale: The correct answer is A: Bacteria. Urinary tract infections (UTIs) are primarily caused by the invasion of bacteria into the urinary tract. Bacteria, especially Escherichia coli (E. coli), are the most common culprits. They enter the urinary tract through the urethra and can multiply in the bladder, leading to infection. Viruses (choice B) and fungi (choice C) are not typical causes of UTIs. "None of the above" (choice D) is incorrect as bacteria are indeed the main cause of UTIs.

Correct Answer: B

Rationale: The correct answer is B because anaerobic bacteria can grow in environments without oxygen. Anaerobic bacteria do not require oxygen for their metabolism and energy production. They can thrive in oxygen-deprived conditions by using alternative electron acceptors. Choice A is incorrect because anaerobic bacteria do not require oxygen to survive. Choice C is incorrect because anaerobic bacteria typically cannot survive in the presence of high concentrations of oxygen. Choice D is incorrect because anaerobic bacteria do not perform photosynthesis.

Correct Answer: D

Rationale: The correct answer is D because enveloped viruses have a lipid bilayer envelope derived from the host cell membrane, which is a complex structure, not exhibiting any specific symmetry. Choice A (cubic symmetry) is incorrect as enveloped viruses do not have any specific geometric shape. Choice B (spiral symmetry) is incorrect as this type of symmetry is typically seen in non-enveloped viruses like helical viruses. Choice C (complex symmetry) is also incorrect as enveloped viruses do not exhibit a specific symmetrical pattern. Therefore, the correct answer is D because enveloped viruses do not have a defined symmetry and can vary in shape and structure.

Correct Answer: B

Rationale: The correct answer is B: Within 24 hours. Rabies post-exposure prophylaxis should ideally be initiated as soon as possible after a potentially infectious bite to prevent the virus from spreading and causing symptoms. Immediate treatment is crucial to prevent the virus from reaching the central nervous system. Waiting beyond 24 hours increases the risk of the virus reaching the brain and becoming fatal. Choices A, C, and D are incorrect because waiting for 6 months, a week, or 2 weeks respectively would significantly delay treatment, allowing the virus to progress and potentially become untreatable.

Correct Answer: B

Rationale: Step 1: Gram-negative, comma-shaped bacterium suggests a curved rod morphology, typical of Campylobacter jejuni. Step 2: Motility is a characteristic of Campylobacter species. Step 3: Campylobacter jejuni is a common cause of bacterial diarrhea in humans. Step 4: Vibrio cholerae causes cholera, not typically associated with comma-shaped morphology. Shigella dysenteriae and Escherichia coli are not comma-shaped.