Six major tyrocidines, purified from the antibiotic tyrothricin complex produced by Bacillus aneurinolyticus, showed significant lytic and growth inhibitory activity towards the gram+ bacteria, Micrococcus luteus and Listeria monocytogenes, but not against the gram- bacterium, Escherichia coli. The isolated natural tyrocidines were in particular more active against the leucocin A (antimicrobial peptide) resistant strain, L. monocytogenes B73-MR1, than the sensitive L. monocytogenes B73 strain. Remarkably similar structure-activity trends toward the three gram+ bacteria were found between growth inhibition and different physicochemical parameters (solution amphipathicity, theoretical lipophilicity, side-chain surface area and mass-over-charge ratio).