This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Mycobacterial Infections, Subject name: Dental
Buruli ulcer is caused by? 
Select and explain. 
A. M. marinum, B. M. ulcerans, C. M. avium intercellulare, D. M. tuberculosis
B: M. ulcerans
Answer: B: M. ulcerans 
Explanation: Buruli ulcer is caused by Mycobacterium ulcerans. Ulcers may be very deep and involve muscle and bone. Skin test with burulin gives positive response.