Final answer:
Lyme disease and syphilis are caused by spirochetes, which are spiral or corkscrew-shaped bacteria. Borrelia burgdorferi causes Lyme disease and Treponema pallidum causes syphilis.
Step-by-step explanation:
Lyme disease and syphilis are caused by spiral or corkscrew bacteria called spirochetes.
These bacteria belong to the genus Borrelia and Treponema. B. burgdorferi, a species of spirochete, causes Lyme disease, while T. pallidum, another species of spirochete, causes syphilis.