In a 35 year old man which is most likely organism causing infection of epididymis-

Chlamydial urethritis may be followed by acute epididymitis, but this condition is rare, generally occurring in sexually active patients <35 years of age; in older men, epididymitis is usually associated with gram-negative bacterial infection and/or instrumentation procedures. It is estimated that 50-70% of cases of acute epididymitis are caused by C. trachomatis . The condition usually presents as unilateral scrotal pain with tenderness, swelling, and fever in a young man, often occurring in association with chlamydial urethritis. The illness may be mild enough to treat with oral antibiotics. (Harrison's Principles of internal medicine,20 th edition, page 1423)