Limitation of adhesion and growth of Listeria monocytogenes on stainless steel surfaces by Staphylococcus sciuri biofilms

The adhesion and subsequent development of Listeria monocytogenes on stainl ess steel was studied in the absence and in the presence of a Staphylococcu s sciuri biofilm. In the three growth media studied, the percentage of adhe rent cells was reduced to nearly the same extent by the presence of 1-day b iofilms of Staph. sciuri for the two strains of L. monocytogenes studied. O ne-day biofilms of Staph. sciuri exhibited the same exopolysaccharide conte nt per square centimetre, although they colonized from 3.5 to 35% of the st ainless steel depending on the growth media. This suggests that extracellul ar substances rather than cell-to-cell interactions were involved in the de creased adhesion. After 3 days of culture, Staphylococcus biofilms prevente d the adherent L. monocytogenes population from increasing within the biofi lm, leading to an average logarithmic cfu difference of 0.9-2.7 between the pure and mixed culture. A competition for nutrients by Staph. sciuri was o bserved in one of the three media. A role for extracellular polysaccharides produced by the Staphylococcus biofilm in preventing the adhesion of L. mo nocytogenes and in modifying the balance existing between its planktonic an d biofilm phase is hypothesized. A higher proportion of L. monocytogenes ce lls was observed in the planktonic phase in mixed cultures, suggesting that the extracellular substances produced by Staph sciuri biofilms and involve d in the decreased adhesion of L. monocytogenes could modify the balance ex isting between planktonic and biofilm populations. In addition, co-cultures of L. monocytogenes and Staph. sciuri in broth showed competition for nutr ients for Staph. sciuri in one of the three media.