Final answer:
The spore form of Clostridium tetani is the most resistant to disinfection, due to the protective nature of endospores.
Step-by-step explanation:
The form of Clostridium tetani that is most resistant to disinfection is the spore form. Species in the genus Clostridium, including C. tetani, are known for their ability to form endospores, which are incredibly resilient and can survive harsh conditions, including those created by many disinfection processes. These endospores are so hard to kill that special sterilization methods are required to ensure they are destroyed.
It is particularly the Clostridium spp.'s production of endospores that makes them prominent among organic forms of bacteria for their resistance to disinfection.