Correct Answer: D

Rationale: The correct answer is D: All of the above. Neisseria meningitidis, Streptococcus pneumoniae, and Haemophilus influenzae are all common causes of bacterial meningitis. Neisseria meningitidis is often associated with outbreaks in community settings. Streptococcus pneumoniae is a leading cause of bacterial meningitis in adults. Haemophilus influenzae used to be a common cause in children before the introduction of the Hib vaccine. Therefore, since all three bacteria are known to cause bacterial meningitis, the correct answer is D. Choices A, B, and C are incorrect because each bacteria individually can cause bacterial meningitis, making "All of the above" the correct comprehensive answer.

Correct Answer: B

Rationale: The correct answer is B because lysozyme, lactoferrin, interferon, and complement are all humoral factors involved in natural resistance. Lysozyme and lactoferrin are antimicrobial proteins that help defend against pathogens. Interferon is a signaling protein that inhibits viral replication, while complement is a group of proteins that enhance the immune response by promoting inflammation and opsonization. Choices A, C, and D are incorrect: - Choice A mentions only macrophages, which are not humoral factors but rather phagocytic cells. - Choice C lists immune cells involved in adaptive immunity (B and T lymphocytes, NK cells) rather than humoral factors of natural resistance. - Choice D includes immunoglobulins, which are part of adaptive immunity, not natural resistance.

Correct Answer: B

Rationale: The correct answer is B: caliciviruses. Caliciviruses are known to be (+) ssRNA viruses that cause gastroenteritis in a wide range of animals, including birds, cats, dogs, pigs, sheep, cows, and humans. These viruses are highly contagious and can spread through contaminated food or water. Rotaviruses (A) are also a common cause of gastroenteritis, but they are not exclusively isolated from the mentioned animals. Adenoviruses (C) typically cause respiratory or eye infections, not gastroenteritis. Noroviruses (D) are also a major cause of gastroenteritis in humans, but they are not commonly found in animals other than humans.

Correct Answer: B

Rationale: The correct answer is B: EBV. Osteomyelitis is primarily caused by bacteria, not viruses like Epstein-Barr virus (EBV). The main pathogens involved in osteomyelitis are typically Staphylococcus aureus, including Methicillin-resistant Staphylococcus aureus (MRSA), Haemophilus influenzae, and Pseudomonas aeruginosa. EBV is not a causative agent of osteomyelitis. It is crucial to differentiate between bacterial and viral etiologies in infectious diseases to guide appropriate treatment.

Correct Answer: D

Rationale: The correct answer is D: Loefler. This staining method is used for identifying Corynebacterium diphtheriae, the causative agent of diphtheria. It involves using methylene blue and basic fuchsin to stain the bacteria. The yellow bacilli with blue grains at their ends indicate the characteristic appearance of C. diphtheriae when stained using the Loefler method. Choice A: Ziehl-Nielsen is used for acid-fast bacteria like Mycobacterium tuberculosis. Choice B: Kozlovsky is not a standard staining method in microbiology. Choice C: Romanovsky is used for blood smears to identify malaria parasites.