Treponema pallidum

Treponema pallidum is a parasitic spirochaete bacterium. There are different kinds of "Treponema pallidum", which cause diseases like syphilis, bejel, pinta and yaws.
The most common disease caused by "Treponema pallidum" is syphilis, a serious sexually transmitted infection. 
Syphilis is treated and cured by taking antibiotics. Usually, the first treatment used is penicillin. Antibiotic resistance has developed to a number of agents. Ceftriaxone, a third-generation cephalosporin antibiotic, may be as effective as penicillin-based treatment.
Pennicilin is still effective, but "the potential of this spirochete to develop additional antibiotic resistance could seriously compromise syphilis treatment and control".