This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bacteria, Subject name: Microbiology
[{'content': 'Most virulent variety of shigellosis is caused by: \nSelect and explain. \nA. S. dysentriae, B. S. sonnei, C. S. flexneri, D. S. boydii', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Shigella dysenteriae(Ref: Ananthanarayan, 8th/e, p. 286 and 9th/e, p. 2851)Complications are most often seen in infection with Sh. dysenteriae type I and include arthritis, toxic neuritis, conjunctivitis, parotitis and in children, intussusception. HUS may occur in severe cases.", 'role': 'assistant'}]