Isolation and characterisation of a novel antibacterial peptide from bovine alpha sub(S1)-casein

Bovine casein was hydrolysed with a range of proteolytic enzymes including pepsin, trypsin, alpha -chymotrypsin and beta -chymotrypsin, and assessed for antibacterial activity. The pepsin digest of bovine casein, which showed antibacterial activity, was fractionated using reverse phase high performance liquid chromatography and the antibacterial peptides isolated were characterised using electrospray ionisation mass spectrometry. Two antibacterial peptides were identified, a novel peptide (Cp1) which corresponded to residues 99-109 of bovine alpha sub(S1)-casein and a previously reported peptide (Cp2) which corresponded to residues 183-207 of bovine alpha sub(S2)-casein. The minimum inhibitory concentration (MIC) of Cp1 and Cp2 were determined against a range of bacterial cultures. Cp1 exhibited an MIC of 125 mu g mL super(-1) against all Gram- positive bacteria tested, and MIC ranging between 125 and >1000 mu g mL super(-1) against the Gram-negative bacteria tested. Cp2 was generally far more potent against the Gram-positive bacteria, exhibiting an MIC of 21 mu g mL super(-1), compared to MICs ranging from 332 to >664 mu g mL super(-1) against most of the Gram- negative bacteria tested.