Natural reservoirs of legionellae are:

Correct Answer: A

Rationale: The correct answer is A because Legionellae are typically found in natural water sources such as lakes, rivers, and soil. Legionellae thrive in aquatic environments and can also be present in mud. Choice B is incorrect as Legionellae are not limited to infected humans but are also found in the natural environment. Choice C is incorrect as Legionellae are not primarily associated with infected animals. Choice D is incorrect as Legionellae do have natural reservoirs in water and soil.

Correct Answer: D

Rationale: Binary fission is the correct answer for bacterial replication because it is the process by which bacteria divide into two identical daughter cells. During binary fission, the bacterial cell replicates its DNA, forms a septum dividing the cell into two, and eventually splits into two daughter cells. This process is specific to prokaryotic cells such as bacteria and is different from mitosis and meiosis, which are processes specific to eukaryotic cells. Cytokinesis is the final step of cell division in both eukaryotes and prokaryotes, but it is not the primary mechanism of bacterial replication.

Correct Answer: C

Rationale: The correct answer is C: Enhancing virulence by preventing phagocytosis. Bacterial capsules help bacteria evade the immune system by preventing phagocytosis, a process where immune cells engulf and destroy pathogens. This enhances the bacteria's virulence and ability to cause infections. Choices A, B, and D are incorrect because bacterial capsules do not directly contribute to protein synthesis, protect against desiccation, or facilitate motility.

Correct Answer: D

Rationale: The correct answer is D because all three choices, Clostridium botulinum, Morbillivirus morbillorum, and Clostridium tetani, can cause infections of the CNS. Clostridium botulinum can lead to botulism, affecting the nervous system. Morbillivirus morbillorum can cause measles, which can lead to encephalitis. Clostridium tetani can cause tetanus, affecting the central nervous system. Therefore, all three choices can cause infections of the CNS. Choices A, B, and C are incorrect individually because each pathogen can cause CNS infections.

Correct Answer: A

Rationale: The correct answer is A: Human papillomavirus. Genital warts are caused by certain strains of HPV, specifically types 6 and 11. HPV is a sexually transmitted infection that affects the skin and mucous membranes. HPV is directly linked to the development of genital warts through skin-to-skin contact during sexual activity. Herpes simplex virus 2 causes genital herpes, not genital warts. Human immunodeficiency virus (HIV) weakens the immune system but does not directly cause genital warts. Human cytomegalovirus (CMV) is not a common cause of genital warts. Therefore, HPV is the correct and most logical choice for the cause of genital warts.