Biol. Pharm. Bull. 29(11) 2160—2167 (2006)

antibiotics with a complex composition and structure and is produced by certain strains of Bacillus licheniformis and Bacillus subtilis. It is mainly active against Gram-positive bacteria. Bc consists of a mixture of structurally similar polypeptides from 12 amino acids (AA). The most important and known component is Bc A (Fig. 1). Other important components are B1, B2 and B3 which together with component A, represent more than 96% of the total antimicrobial activity in commercial products. Bc is often available in the form of a more stable complex with Zn (ZnBc). The basic structure of Bc consists of seven AA membered ring and five amino acids in the side chain. The terminal part of the side chain ends with thiazoline ring, consisting of L-cysteine and L-isoleucine or of L-cysteine and L-valine (Fig. 1). Ikai and co-workers determined the structure, sequence of amino acids and molecular weights of 15 major and minor Bc components using FAB, LC/MS and MS/MS. The above mentioned polypeptide components are structurally very similar and they differ from each other only in the substitution of one to three of L-isoleucines by L-valine in the side chain or in the ring of 7 AA or in the terminal thiazoline ring (Fig. 1). Recently the nomenclature for three minor components D1, D2 and D3 has been changed to C1, C2 and C3 respectively in the PharmEuropa and in the Ph.Eur. 5. Bacterial resistance against antibiotics has become a serious health issue in recent years. However, bacterial resistance to bacitracin is still scarce despite its great and wide use in human and veterinary medicine, as well as in animal feed additives over the past several decades. In general, it is true that resistance to peptide antibiotics occurs 2160 Vol. 29, No. 11