Bacitracin
Bacitracin is a cyclic peptide antibiotic first described in 1945, isolated from Bacillus subtilis. It's mechanism of action is to interrupt the dephosphorylation of C55-isoprenyl pyrophosphate, which is used in the construction of the peptidoglycan component of the bacterial cell wall.
References
- http://science.sciencemag.org/content/102/2650/376