Lactococcus lactis ssp. cremoris MG1363 harbouring pCI658, a 58 kb plasmid originating in L. lactis ssp. cremoris HO2, adsorbs phages phi 712 (936 phage species) and phi c2 (c2 species) less efficiently than the plasmid-free phage sensitive strain. The presence of an alkali-soluble loose 'fluffy' pellet following centrifugation of the phage resistant derivative was established. In addition this pCI658-containing strain possessed a more hydrophilic cell surface and did not agglutinate with the glucosyl-specific lectin concanavalin A. Furthermore, electron micrographs also illustrated significant plasmid-mediated alterations of the cell surface. HPLC analysis of the loosely associated extracellular material revealed that galactose and glucuronic acid appeared to be its major components. It was concluded that pCI658 encodes the production of a hydrophilic exopolysaccharide which masks cell surface receptors causing a dramatic decrease in bacteriophage adsorption. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.