Bacitracin is a complex of cyclic peptides isolated from Bacillus licheniformis, first published in 1945 as active against Gram-positive bacteria, including β-haemolytic streptococci, gonococci and meningococci. The structure of the bacitracins was finally elucidated in 1995. Bacitracin forms a complex with C55-isoprenyl pyrophosphate and a metal ion to inhibit dephosphorylation and transport of polysaccharides, peptidoglycans and lipopolysaccharides to the growing cell wall. Bacitracin is used clinically as a topical treatment for skin infections.