A patient presents with a history of diarrhea of several weeks duration. Which of the following may be the cause?

Correct Answer: A

Rationale: Rationale: - Yersinia enterocolitica is a common cause of diarrhea due to contaminated food or water. - It typically presents with symptoms such as abdominal pain, fever, and diarrhea. - The other choices are unlikely causes of prolonged diarrhea, as Bordetella pertussis causes whooping cough, Neisseria meningitidis causes meningitis, and Corynebacterium diphtheria causes diphtheria.

Correct Answer: D

Rationale: The correct answer is D: Rubella virus. Rubella virus does not belong to the family Paramyxoviridae because it belongs to the Togaviridae family. The other choices, A (Measles virus), B (Respiratory syncytial virus), and C (Mumps virus) are all members of the Paramyxoviridae family. This classification is based on the genetic and structural characteristics of the viruses. Rubella virus is distinct in its genetic composition and replication cycle compared to the Paramyxoviridae family, making it the correct choice.

Correct Answer: C

Rationale: Legionella pneumophila is a Gram-negative coccobacillus. It is not a coccus (round shape), spiral bacterium, or Gram-positive coccobacillus. The correct answer is C because Legionella pneumophila has a characteristic coccobacillary shape and stains Gram-negative due to its cell wall composition. The other choices are incorrect because they do not accurately describe the morphology or staining characteristics of Legionella pneumophila.

Correct Answer: D

Rationale: Rationale: 1. Rickettsiae are obligate intracellular bacteria, hence they do not form spores, capsules, or flagella. 2. They have a slim glycocalyx layer, aiding in attachment to host cells. 3. Bipolar fimbriae are structures that help in adhesion to host cells. Therefore, all statements (A, B, and C) are true for Rickettsiae, making option D the correct answer. Other choices are incorrect as they do not accurately describe the characteristics of Rickettsiae.

Correct Answer: C

Rationale: The correct answer is C because Leptospira cannot be cultivated on blood and chocolate agar. The bacterium requires specialized media such as Ellinghausen-McCullough-Johnson-Harris (EMJH) medium for growth. Blood and chocolate agar do not provide the necessary nutrients for the bacterium's growth. Leptospira is a fastidious organism that has unique culture requirements. Therefore, the statement that Leptospira can be cultivated on blood and chocolate agar is incorrect. The other choices are correct: A - Leptospirosis is an acute infectious disease with a typical geographic distribution, B - Reservoirs of leptospira are different wild and domestic animals, mainly rodents, and D - Doxycycline and penicillins are drugs of choice for the treatment of leptospirosis.