Correct Answer: C

Rationale: Toxoplasma gondii is a protozoan parasite known to cause toxoplasmosis. It belongs to the group of eukaryotic organisms called protozoans because it is a single-celled organism with complex cellular structures. Protozoans are characterized by their ability to move and perform essential functions independently. Algae (choice A) are photosynthetic eukaryotic organisms, fungi (choice B) are non-photosynthetic eukaryotes that include molds and yeasts, and helminths (choice D) are multicellular parasitic worms. Therefore, the correct answer is C because Toxoplasma gondii is a protozoan parasite.

Correct Answer: A

Rationale: The correct answer is A: Anatoxin. An anatoxin is a preparation that contains inactivated toxins produced by the anthrax-causing bacteria. By administering anatoxin, the population can develop immunity against the toxin without being exposed to the live bacteria. This specific prophylaxis approach helps prevent the development of anthrax infection by targeting the toxin itself. Summary: - Choice B (Inactivated vaccine) is incorrect because an inactivated vaccine typically contains killed or inactivated whole bacteria, not just the toxins. - Choice C (Chemical vaccine) is incorrect as there is no such thing as a chemical vaccine; vaccines are biological preparations. - Choice D (Genetically engineered vaccine) is incorrect because while vaccines can be genetically engineered, the specific term "genetically engineered vaccine" does not accurately describe the prophylaxis used against anthrax in this scenario.

Correct Answer: B

Rationale: The correct answer is B: pertussis toxin. This toxin is the most important virulence factor of Bordetella pertussis because it plays a key role in causing the characteristic symptoms of whooping cough. Pertussis toxin interferes with the host's immune response, leading to inflammation and tissue damage in the respiratory tract. The other choices (A: the flagellum, C: P fimbriae, D: mannose-resistant adhesins) are important for bacterial attachment and colonization, but they do not directly contribute to the severity of the disease like pertussis toxin does.

Correct Answer: D

Rationale: The correct answer is D, "All of the above." Bacterial meningitis can be caused by Neisseria meningitidis, Haemophilus influenzae, and Streptococcus pneumoniae. These bacteria are common pathogens associated with meningitis. Each of them can lead to serious infections in the brain and spinal cord. Neisseria meningitidis is known for causing meningococcal meningitis, Haemophilus influenzae is a common cause of H. influenzae meningitis, and Streptococcus pneumoniae is responsible for pneumococcal meningitis. Therefore, since all three bacteria can cause bacterial meningitis, the correct answer is D. Choices A, B, and C are incorrect because each of these bacteria individually can cause bacterial meningitis; it is not limited to just one specific type.

Correct Answer: C

Rationale: Rationale: 1. Pseudomonas aeruginosa is commonly found in hospital environments. 2. It is an opportunistic pathogen causing various nosocomial infections. 3. Its ability to develop resistance to antibiotics makes it a significant threat. 4. Corynebacterium diphtheriae causes diphtheria, not common nosocomial infections. 5. Shigella sonnei causes foodborne illness, not typically nosocomial infections. 6. "None of the above" is incorrect as Pseudomonas is indeed commonly associated with nosocomial infections.