Of >500 bacterial isolates from seaweed, namely Fucus serratus, algae (Halimeda sp, Sargassum sp), sponges (Siphonochalina sp, Leucetta 'chgosensis), sea cucumber, (Holothuria atra), star fish (Acanthaster planci), mangrove (Avecenia marina) roots, sea anemone, (Heteractis magnifica), ,jellyfish (Disambiguation), sediment and seawater from the Scottish and Saudi Arabian coasts, a culture of Bacillus licheniformis produced a novel protein with antibacterial activity against methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci and Listeria monocytogenes. The antibacterial activity was maximal in cultures prepared in Columbia broth -containing pieces of synthetic polyurethane sponge and shaken at 210-230 rpm. Antibacterial activity was not found in cultures grown statically or with different speeds of rotary shaking. Reduced activity was apparent in supernatants prepared from marine . 2216E broth and tryptone soya broth with or without 1% (w/v) sodium chloride. The antibacterial compound was sensitive to proteinase K, pronase and trypsin, but was not affected by Tween 20, 40, 60 or 80, or a- or ~-amylase. Activity was not adversely affected by heating to 40°C or treatment at pH 5-14. The bioactive compound was purified by gel filtration and ion exchange, and classified by using MALDI-TOF determined as a protein of 30.7 kDa, which had homology to the YbdN protein of B. licheniformis ATCC 14580. The gene encoding YbdN was isolated and transferred to Escherichia coli XL BLUE, and the product was purified by SDS-PAGE giving a single band with a molecular size 30.7 kDa.