Dual-species biofilms formation by Escherichia coli O157:H7 and environmental bacteria isolated from fresh-cut processing plants

Authors: LIU, NANCY - University Of Maryland; Nou, Xiangwu; Lefcourt, Alan; Shelton, Daniel; LO, MARTIN - University Of Maryland

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/2013
Publication Date: 11/18/2013
Citation: Liu, N.T., Nou, X., Lefcourt, A.M., Shelton, D.R., Lo, M. 2013. Dual-species biofilms formation by Escherichia coli O157:H7 and environmental bacteria isolated from fresh-cut processing plants. International Journal of Food Microbiology. 171:15-20.

Interpretive Summary: Biofilm formation is an important mechanism for bacterial survival in stressful environments. Although some pathogens have the ability to form biofilms, most do not. However, biofilms typically are composed of many different bacterial strains, some of which could be pathogens. In this this study we investigated the ability of pathogenic E. coli O157:H7 strains (normally poor biolfims formers) to interact with Ralstonia insidiosa, a common environmental bacterium found in fruit processing facilities and prolific biofim former. When cultured together, the pathogenic E.coli were readily incorporated into biofilms with R. insidiosa. There was no apparent benefit to R. insidiosa, but the interaction clearly enhanced survival of the pathogenic E.coli. These types of interactions could be one of the mechanisms for the persistence of foodborne pathogens in food processing environments. This information will be useful to other scientists, regulatory agencies and the fruit processing industry.

Technical Abstract: Biofilm formation is a mechanism adapted by many microorganisms that enhances the survival in stressful environments. In food processing facilities, bacterial strains with strong biofilm forming capacities are more likely to survive the daily cleaning and disinfection. Foodborne bacterial pathogens, of which many are poor biofilm formers, could potentially take advantage of this protective mechanism by interacting with other strong biofilm producers. The objective of this study was to determine the influence of bacteria native to fresh produce processing environments on the incorporation of Escherichia coli O157:H7 in biofilms. Bacteria strains representing 13 Gram-negative species isolated from two fresh produce processing plants in a previous study were tested for forming dual-species biofilms with E. coli O157:H7. A sublet of the tested strong biofilm producers, including strains of Burkholderia caryophylli and Ralstonia insidiosa, significantly enhanced biofilm formation when co-cultured with E. coli O157:H7, as reflected by 63-180% increase in biomass compared to the respective monoculture biofilms. This synergistic increase of biomass in the dual-species biofilms was often correlated to significantly increased incorporation of E. coli O157:H7 cells in the biofilm. Co-culturing E. coli O157:H7 strain FS4052 with Ralstonia insidiosa, the bacterial species frequently isolated from the fresh produce processing plants, increased the presence of E. coli O157:H7 cells in biofilms by 0.96 log10 units (p<0.05) and resulted in significant increase in the thickness (p<0.05) of dual-species biofilms compared to monoculture biofilms. While some environmental isolates with strong biofilm formation ability failed to increase the incorporation of E. coli O157:H7 into biofilms, all tested E. coli O157:H7 strains consistently exhibited increased presence in dual-species biofilms formed with R. insidiosa. These observations support the notion that E. coli O157:H7 and specific strong biofilm producing bacteria can interact in the formation of biofilms, and suggest a route for increased survival potential of E. coli O157:H7 in fresh produce processing environments.