Correct Answer: D

Rationale: The correct answer is D: scanning electron microscope. A scanning electron microscope provides a three-dimensional image of a specimen by scanning a focused electron beam across the surface of the specimen, detecting the electrons that are emitted from the surface, and creating a detailed image. This is achieved through the detection of secondary electrons, backscattered electrons, and X-rays emitted from the specimen surface. A dark-field microscope (choice A) utilizes oblique lighting to enhance contrast and is not specifically designed to provide a 3D image. A transmission electron microscope (choice B) uses a beam of electrons transmitted through a specimen to create a 2D image at high magnification. A bright-field microscope (choice C) is a basic microscope that illuminates a specimen with uniform light and does not provide a 3D image like a scanning electron microscope does.

Correct Answer: C

Rationale: Step 1: Antitetanus serum is crucial for patients with open maxillofacial trauma to prevent tetanus infection from contaminated wounds. Step 2: Antibiotics are needed to prevent infection in the wound. Step 3: Antitetanus serum provides immediate passive immunity while antibiotics help combat potential infections. Step 4: Antitetanus immunoglobulin is not mentioned in the question and is not typically used for prophylaxis. Step 5: Anticonvulsive drugs are not preventive medications for maxillofacial trauma. Step 6: Diphtheria, tetanus, and pertussis vaccines are not specifically indicated for immediate prevention in this scenario.

Correct Answer: C

Rationale: The correct answer is C: Staphylococcus saprophyticus. The rationale is that Staphylococcus saprophyticus is the only one among the listed species that is known to be resistant to novobiocin. This resistance is due to the specific mechanism of action of novobiocin, which targets DNA gyrase, and Staphylococcus saprophyticus possesses an altered DNA gyrase enzyme that renders it resistant to the antibiotic. Staphylococcus aureus and Staphylococcus epidermidis are susceptible to novobiocin, making choices A and B incorrect. Choice D, "none of the listed," is also incorrect as Staphylococcus saprophyticus is indeed resistant to novobiocin.

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: B

Rationale: The correct answer is B because the main target of the toxin produced by Vibrio cholerae is the epithelial cells of the small intestine. This toxin, known as cholera toxin, binds to the surface of these cells and disrupts their normal function, leading to the characteristic watery diarrhea seen in cholera. The other choices are incorrect because macrophages are not the main target, RBCs are not directly affected by the toxin, and the stomach epithelial cells are not specifically targeted by Vibrio cholerae toxin.