Correct Answer: A

Rationale: The correct answer is A: Lowestein-Jensen. This is because Lowestein-Jensen medium is specifically designed to cultivate Mycobacterium tuberculosis, providing necessary nutrients and conditions for its growth. Loefller's medium is not optimal for cultivating M. tuberculosis. Choice C (All of the above) is incorrect as not all the options listed are suitable for cultivating M. tuberculosis. Choice D (None of the above) is also incorrect as Lowestein-Jensen is indeed the recommended growth medium for this bacterium.

Correct Answer: D

Rationale: The correct answer is D: Cytoplasmic membrane - essential. The cytoplasmic membrane is a crucial structure in bacteria as it regulates the passage of substances in and out of the cell, provides structural support, and is essential for maintaining cell integrity. Without a functional cytoplasmic membrane, bacteria would not be able to survive. A: Nucleus is incorrect because bacteria do not have a true nucleus. B: Capsule - non-essential is incorrect because while the capsule provides protection and helps in adherence, it is not essential for bacterial survival. C: Mitochondria is incorrect because bacteria do not have mitochondria; they generate energy through other mechanisms. In summary, the cytoplasmic membrane is essential for bacterial survival, making it the correct choice among the options provided.

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: C

Rationale: The correct answer is C: Van Leeuwenhoek. Van Leeuwenhoek was a Dutch scientist known for his pioneering work in microscopy. He was the first to observe microbial life, including bacteria on teeth, using his handmade microscopes in the 17th century. Jenner (choice A) is known for developing the smallpox vaccine, not for microbial observations. Semmelweis (choice B) discovered the importance of handwashing in preventing infections. Pasteur (choice D) is famous for his work on pasteurization and germ theory, but not specifically for observing microbial life on teeth. Van Leeuwenhoek's meticulous observations and groundbreaking discoveries make him the correct choice in this context.

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.