The novel ester (E)-phytol (5Z,8Z,11Z,14Z,17Z)-eicosapentaenoate++ + (1); (6Z,9Z,12Z,15Z)-hexadecatetraenoic acid; (6Z,9Z,12Z,15Z)-octadecatetraenoic acid; and (6Z,9Z,12Z)-hexadecatrienoic acid isolated from the diatom Navicula delognei f. elliptica, show significant antibacterial activity against