This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
[{'content': 'All of the following proteus species forms indole EXCEPT: September 2004 \nSelect and explain. \nA. P. mirabilis, B. P. vulgaris, C. P. rettgeri, D. P. morganii', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. A i.e. P. mirabilis', 'role': 'assistant'}]