Enhanced biofilm formation in dual-species culture of Listeria monocytogenes and Ralstonia insidiosa .

In the natural environments microorganisms coexist in communities as biofilms. Since foodborne pathogens have varying abilities to form biofilms, investigation of bacterial interactions in biofilm formation may enhance our understanding of the persistence of these foodborne pathogens in the environment. Thus the objective of this study was to investigate the interactions between Listeria monocytogenes and Ralstonia insidiosa in dual species biofilms. Biofilm development after 24 h was measured using crystal violet in 96-well microtiter plate. Scanning electron microscopy and cell enumeration were employed after growth on stainless steel coupons. When compared with their single species counterparts, the dual species biofilms exhibited a significant increase in biofilm biomass. The number of L. monocytogenes in co-culture biofilms on stainless steel also increased significantly. However, there was no effect on the biofilm formation of L. monocytogenes when cultured with R. insidiosa separated by a semi-permeable membrane-linked compartment or cultured in R. insidiosa cell-free supernatant, indicating that direct cell-cell contact is critical for this interaction.