Final answer:
Syphilis cannot be contracted from a toilet seat because its causative agent, Treponema pallidum, is inactivated in dry environments and is transmitted through direct contact with infectious sores.
Step-by-step explanation:
A client who has syphilis cannot contract it from a toilet seat because the causative agent of syphilis, the bacterium Treponema pallidum, is inactivated when exposed to a dry environment. Syphilis is transmitted from person to person by direct contact with a syphilitic sore, known as a chancre, which can occur on the genitals, mouth, or anus. It cannot survive on surfaces like toilet seats because the bacterium requires a wet environment to remain viable and is rapidly inactivated in the absence of moisture and human body contact.