1. Treponema pallidum is a spirochete bacterium that causes syphilis. It has four subspecies that can cause different diseases. 2. Syphilis progresses through primary, secondary, latent, and tertiary stages. The primary stage involves painless sores called chancres. Secondary syphilis has a widespread rash. 3. Penicillin is the treatment of choice for syphilis. Early syphilis is treated with benzathine penicillin injections or oral antibiotics.