How does penicillin treat syphilis?

Syphilis is a systemic disease caused by the spirochete bacterium Treponema pallidum. Penicillin acts as an effective treatment by killing these spirochetes, thereby stopping the progression of the infection at any stage.12

When administered—typically via injection—penicillin targets the bacteria directly, preventing them from reproducing and remaining in the body's tissues. While this treatment is highly successful at eliminating the causative organism, it is important to note that penicillin cannot repair neurological or other physical damage that may have already occurred due to the disease in its late stages. The discovery that penicillin could effectively treat syphilis, first demonstrated in 1943, transformed the condition from a potentially lifelong affliction into a manageable and curable infection.213