Abstract: The present invention relates generally to the field of health promoting agents, in particular antimicrobial agents and provides antimicrobial peptides and bacterial strains that provide the antimicrobial peptides. In one aspect, the invention provides a biologically pure culture of Lactobacillus acidophilus, strain DPC6026, a sample of which has been deposited at the National Collection of Industrial and Marine Bacteria, Aberdeen, Scotland on 18th Nov. 2005 under the accession number NCIMB 41354, or a derivative or mutant thereof capable of producing from milk or a milk product, peptides having antimicrobial activity.