This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bacteriology, Subject name: Medicine
[{'content': 'Reactive arthritis is usually caused by - \nSelect and explain. \nA. Shigella flexneri, B. Shigella boydii, C. Shigela shiga, D. Shigela dysentriae', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e.. Shigella Flexneri o Organisms that have been associated with Reiter Arthritis include the follow ing:C trachomatis (L2b serotype)Ureaplasma urealyticumNeisseria gonorrhoeaeShigella flexneriSalmonella enterica serovars TyphimuriumMycoplasma pneumoniaeMycobacterium tuberculosisYersinia enterocolitica and pseudotuberculosisCampylobacter jejuniClostridium difficileBeta-hemolytic (example, group A) and viridans streptococci", 'role': 'assistant'}]