Ralstonia insidiosa serves as bridges in biofilm formation by foodborne pathogens Listeria monocytogenes, Salmonella enterica, and Enterohemorrhagic Escherichia coli

Abstract

Biofilm formation on abiotic surfaces in fresh produce processing facilities may play a role in foodborne outbreaks by providing protective microniches for pathogenic bacteria. Our previous study showed that a strain of Ralstonia insidiosa isolated from a fresh produce processing plant could enhance the incorporation of Escherichia coli O15:H7 in biofilms under various environmental conditions. These results raised the concern that R. insidiosa might have the ability to incorporate other foodborne pathogens and promote their survival and growth in biofilms. To test this hypothesis, 6 strains of Shiga toxin producing E. coli, 2 strains of Salmonella, and 6 strains of Listeria monocytogenes were examined for dual-species biofilm formation with R. insidiosa. A significant increase in biomass formation was observed in 7 of the 14 R. insidiosa-pathogen combinations, while significantly enhanced incorporation of pathogenic cells into biofilms was seen in 12 of the 14 R. insidiosa-pathogen combinations. The synergistic interactions between R. insidiosa and the tested foodborne pathogens seemed dependent on intimate cellular contact between the two strains. Overall, this study showed that R. insidiosa could enhance the incorporation of biofilms of different types of foodborne pathogenic bacteria and should be considered a bridging bacterium for biofilm formation in various food processing environments.