Clostridium tetani bacteria are infectious but non-contagious, which is otherwise unprecedented among infections preventable by vaccination.
Survival of tetanus does not mean the host organism has developed immunity to tetanus, vaccination via the tetanospasmin toxoid is still required to induce immunity.
The tetanospasmin toxic is unique to C. tetani and serves no purpose benefiting the bacteria.
Tetanospasmin is extremely potent and the only stronger toxins are those of Clostridium botulinum (botulinum toxin - Botulism) and Corynebacterium diphtheriae (diptheria exotoxin - Diptheria).
C. tetani and C. botulinum are very similar organisms and are closer in relation than other bacteria of the Clostrium genus.
It is common misconception that stepping on a rusty nail or wounds caused by rusty objects will cause tetanus. Rusty objects may allow for C. tetani infections given the infection-friendly nature of the wound, but it is not likely that the rusty objects are actually carrying the bacteria to cause the infection resulting in tetanus.
An interesting utility of C. tetani is the continuation of the carbon cycle via biodegradation of dead organic material by the bacteria that allows for carbon to be provided to producer organisms.
If you are looking for more information on Clostridum tetani, I recommend you visit these sites:
Wikipedia: Clostridium tetani
Bacteriology at UW - Madison: Tetanus
Bacteriology at UW - Madison: Pathogenic Clostridia
If you found Clostridum tetani interesting, I recommend you check out these pathogenic bacteria:
Clostridium botulinum
Bacillus anthracis
Mycobacterium tuberculosis
