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
A 20-year-old male who works as a truck driver presented to the skin and venereal disease OPD with a genital ulcer, which was painless for the last 10 days. He had unprotected sexual contact with a commercial sex worker about 2 weeks previously. On examination the ulcer was found to be circumscribed, indurated and partially healed. The inguinal lymph nodes were enlarged. What would be probable cause of infection on the basis of history and genital lesion? 
Select and explain. 
A. HIV, B. HPV, C. Treponema pallidum, D. HSV-2
C: Treponema pallidum
Answer: C: Treponema pallidum 
Explanation: Ans. is 'c' i.e., Treponema pallidumImage description - Chancre - A primary sore or ulcer at the site of entry of T. pallidum and it begins as a painless papule that rapidly becomes ulcerated, hard and indurated and it is very rich in T. pallidum.