Examination of a man revealed a protozoan disease that affected brain and caused vision loss. Blood analysis revealed unicellular half-moon-shaped organisms with pointed end. The causative agent of this disease is:

Correct Answer: A

Rationale: The correct answer is A: Toxoplasma. Toxoplasma gondii is a protozoan parasite that can infect the brain and cause vision loss. The description of half-moon-shaped organisms with a pointed end matches the appearance of Toxoplasma under the microscope. Toxoplasma is known to cause a condition called toxoplasmosis, which can lead to neurological symptoms such as vision loss. Leishmania, Lamblia, Amoeba, and Trichomonad are not known to cause brain infections or vision loss, making them incorrect choices.

Correct Answer: C

Rationale: The correct answer is C: Escherichia coli. E. coli is the most common cause of acute cystitis. It typically presents with leukocytes and gram-negative bacilli in the urine. The green pigment production indicates pyocyanin, which is a characteristic of E. coli. Pseudomonas aeruginosa (A) can also produce green pigment, but it is less common in urinary tract infections. Proteus mirabilis (B) is associated with a swarming motility pattern on agar, not mucous colonies. Klebsiella pneumoniae (D) is associated with pneumonia and other respiratory infections, not cystitis.

Correct Answer: A

Rationale: The correct answer is A: Candida. The whitish spots resembling coagulated milk on the mucous membranes are characteristic of oral thrush, a condition caused by Candida species. Candida is a gram-positive oval yeast-like fungus commonly found in the oral cavity. Staphylococci (B) are gram-positive cocci, not yeast-like cells. Diphtheria bacillus (C) causes diphtheria, not oral thrush. Actinomycetes (D) are filamentous bacteria, not yeast-like cells typically seen in oral thrush. Therefore, A is the correct answer based on the clinical presentation and microscopic findings.

Correct Answer: A

Rationale: The correct answer is A: Hemolytic streptococci. Hemolytic streptococci are pathogenic bacteria that can cause severe infections in humans, indicating direct epidemiological danger. Hemolytic streptococci are commonly found in the respiratory tract and can be transmitted through the air, making them a good indicator of pathogenic microorganisms in the air. Summary: - B: Sarcina, molds, yeast, and Micrococci are not typically indicators of direct epidemiological danger related to pathogenic microorganisms in the air. - Hemolytic streptococci, on the other hand, are pathogenic bacteria that can cause serious infections and are commonly transmitted through the air, making them a suitable indicator in this context.