Correct Answer: A

Rationale: The correct answer is A: Entamoeba histolytica. This protozoon is known to cause amoebic dysentery, presenting symptoms of weakness, intestinal pain, and indigestion. The presence of microbial cysts with four nuclei in fecal samples is characteristic of Entamoeba histolytica. These cysts are the infective form of the parasite and can cause severe invasive disease in the intestines. Incorrect choices: B: Entamoeba coli does not typically cause invasive disease or severe symptoms like those described in the question. C: Balantidium is a ciliated protozoan that causes balantidiasis, which presents differently from the symptoms described in the question. D: Trichomonad is a flagellated protozoan that typically infects the urogenital tract, not the intestine, and does not form cysts with four nuclei. In summary, the key clues in the question were the symptoms of weakness, intestinal pain,

Correct Answer: A

Rationale: The correct answer is A: Clostridium tetani. Clostridium tetani is responsible for causing tetanus due to its production of tetanospasmin toxin. This neurotoxin leads to muscle stiffness and spasms characteristic of tetanus. Clostridium perfringens is associated with gas gangrene, not tetanus. Streptococcus pyogenes causes strep throat and skin infections, not tetanus. Escherichia coli is a common gut bacteria and is not responsible for tetanus. Therefore, choice A is the correct answer for causing tetanus.

Correct Answer: A

Rationale: The correct answer is A: Neisseria meningitidis. This bacterium is a Gram-negative diplococcus commonly associated with meningitis. The patient's symptoms of fever, headache, and neck stiffness are classic signs of meningococcal meningitis. Neisseria meningitidis is known to cause outbreaks in crowded settings. Streptococcus pneumoniae (Choice B) is a common cause of bacterial meningitis but typically appears as Gram-positive cocci. Haemophilus influenzae (Choice C) can also cause meningitis but is more commonly seen in unvaccinated children. Klebsiella pneumoniae (Choice D) is a Gram-negative bacterium but is not a typical causative agent of meningitis.

Correct Answer: A

Rationale: The correct answer is A: Alexander Fleming. He discovered the antibiotic properties of Penicillium in 1928. Fleming observed that a mold called Penicillium notatum inhibited the growth of bacteria, leading to the discovery of penicillin. Louis Pasteur is known for his work on pasteurization and microbiology, not penicillin. Joseph Lister is known for pioneering antiseptic surgery techniques. Edward Jenner is known for developing the smallpox vaccine, not penicillin. Fleming's discovery revolutionized medicine by introducing the first antibiotic, penicillin, which has saved countless lives.

Correct Answer: A

Rationale: The correct answer is A: Wasserman test, IFT. The patient's symptoms of diffuse alopecia and Pinkus' sign are suggestive of secondary syphilis. The Wasserman test and Immunofluorescence Test (IFT) are used to detect antibodies against Treponema pallidum, the bacterium causing syphilis. This would confirm or rule out syphilis as the underlying cause of the patient's symptoms. Choice B (T.pallidum Immobilization Test) is similar to the Wasserman test but less commonly used. Choice C (Detection of the nasal mucous membrane for M.leprae) is irrelevant as leprosy does not present with the described symptoms. Choice D (Consultation of neuropathist) is premature without ruling out syphilis first. Thus, the Wasserman test, IFT should be the initial examination to investigate the likely cause of the patient's symptoms.