<jats:title>ABSTRACT</jats:title> <jats:p> Twenty-seven marine sediment- and sponge-derived actinomycetes with a preference for or dependence on seawater for growth were classified at the genus level using molecular taxonomy. Their potential to produce bioactive secondary metabolites was analyzed by PCR screening for genes involved in polyketide and nonribosomal peptide antibiotic synthesis. Using microwell cultures, conditions for the production of antibacterial and antifungal compounds were identified for 15 of the 27 isolates subjected to this screening. Nine of the 15 active extracts were also active against multiresistant Gram-positive bacterial and/or fungal indicator organisms, including vancomycin-resistant <jats:italic>Enterococcus faecium</jats:italic> and multidrug-resistant <jats:italic>Candida albicans</jats:italic> . Activity-guided fractionation of fermentation extracts of isolate TFS65-07, showing strong antibacterial activity and classified as a <jats:italic>Nocardiopsis</jats:italic> species, allowed the identification and purification of the active compound. Structure elucidation revealed this compound to be a new thiopeptide antibiotic with a rare aminoacetone moiety. The <jats:italic>in vitro</jats:italic> antibacterial activity of this thiopeptide, designated TP-1161, against a panel of bacterial strains was determined.