Effects of Environmental Parameters on the Dual-Species Biofilms Formed by Escherichia coliO157:H7 and Ralstonia insidiosa,a Strong Biofilm Producer Isolated from a Fresh-Cut Produce Processing Plant

Biofilm-forming bacteria resident to food processing facilities are a food safety concern due to the potential of biofilms to harbor foodborne bacterial pathogens. When cultured together, Ralstonia insidiosa,a strong biofilm former frequently isolated from produce processing environments, has been shown to promote the incorporation of Escherichia coliO157:H7 into dual- species biofilms. In this study, interactions between E. coliO157:H7 and R. insidiosawere examined under different incubating conditions. Under static culture conditions, the incorporation of E. coliO157:H7 into biofilms with R. insidiosawas not significantly affected by either low incubating temperature (10°C) or by limited nutrient availability. Greater enhancement of E. coliO157:H7 incorporation in dual-species biofilms was observed by using a continuous culture system with limited nutrient availability. Under the continuous culture conditions used in this study, E coliO157:H7 cells showed a strong tendency of colocalizing with R. insidiosaon a glass surface at the early stage of biofilm formation. As the biofilms matured, E coliO157:H7 cells were mostly found at the bottom layer of the dual-species biofilms, suggesting an effective protection by R. insidiosain the mature biofilms.