During a microscopy session, spiral-shaped bacteria with loose coils and pointed ends were observed in a blood smear. What is the most likely diagnosis?

Correct Answer: B

Rationale: The correct answer is B: Leptospirosis. Spiral-shaped bacteria with loose coils and pointed ends are characteristic of Leptospira interrogans, the causative agent of Leptospirosis. This bacterium is typically found in contaminated water or soil and can infect humans through contact with infected animals or water. Syphilis (Choice A) is caused by the spirochete Treponema pallidum, which has a more tightly coiled shape and does not typically appear loose or pointed. Relapsing fever (Choice C) is caused by Borrelia species, which are also spirochetes but do not have the loose coils and pointed ends described. Lyme disease (Choice D) is caused by Borrelia burgdorferi, which, like Relapsing fever, does not match the morphology described.

Correct Answer: A

Rationale: The correct answer is A: Wright's agglutination reaction. For brucellosis diagnosis, this test detects antibodies against Brucella species. Wright's test specifically targets agglutinins, which are produced in response to Brucella infection. The other choices are incorrect because: B: Widal's test is used for typhoid fever caused by Salmonella typhi. C: Ascoli's test is for pneumococcal infections. D: Weigl's test is used for typhus fever caused by Rickettsia prowazekii.

Correct Answer: A

Rationale: The correct answer is A: Escherichia coli. Step-by-step rationale: 1. Gram-negative rods: E. coli is a Gram-negative rod bacterium. 2. Fermented lactose: E. coli is known to ferment lactose. 3. Common cause of diarrhea: E. coli is a common causative agent of infectious diarrhea. Summary: B: Salmonella typhi causes typhoid fever, not typically associated with lactose fermentation. C: Shigella dysenteriae causes dysentery, not known for lactose fermentation. D: Proteus vulgaris is not a common cause of infectious diarrhea and does not typically ferment lactose.

Correct Answer: C

Rationale: Rabbit fever, or tularemia, is caused by Francisella tularensis. This bacterium is known to infect a wide range of animals, including rabbits. The other choices, Bartonella henselae (causes cat scratch fever), Spirillum minus (causes rat bite fever), and Yersinia pestis (causes plague) are not associated with rabbit fever. Therefore, the correct answer is C based on the specific pathogen responsible for causing tularemia.

Correct Answer: A

Rationale: The correct answer is A because significant bacteriuria is defined as having more than 10^5 cells in 1 ml of midstream morning urine. This concentration indicates a true infection rather than contamination. Choice B is incorrect because the amount of urine does not determine significant bacteriuria. Choice C is incorrect because even a single bacterium in urine does not necessarily indicate an infection. Choice D is incorrect because not all statements are correct; only choice A accurately defines significant bacteriuria based on the bacterial concentration in urine samples.