Lactococcus lactis subsp. cremoris strain MA39 produces an extracellular polysaccharide containing rhamnose, glucose and galactose. A 16.5 kb plasmid encoding exopolysaccharide production in MA39 was determined by plasmid curing experiments. Phage adsorption assays showed that four different lactococcal phages were adsorbed to MA39-40; only the 16.5 kb plasmid cured an exopolysaccharide non-producing mutant of strain MA39, with high efficiency (93.2-98.5%) while adsorption of these phages was completely inhibited in the wild type strain MA39. These results suggest that exopolysaccharide prevents phage adsorption by masking phage receptor sites.

Lactococcus lactis subsp. cremoris strain MA39 produces an extracellular polysaccharide containing rhamnose, glucose and galactose. A 16.5 kb plasmid encoding exopolysaccharide production in MA39 was determined by plasmid curing experiments. Phage adsorption assays showed that four different lactococcal phages were adsorbed to MA39-40; only the 16.5 kb plasmid cured an exopolysaccharide non-producing mutant of strain MA39, with high efficiency (93.2-98.5%) while adsorption of these phages was completely inhibited in the wild type strain MA39. These results suggest that exopolysaccharide prevents phage adsorption by masking phage receptor sites.