Title: Synergistic interaction in dual-species biofilms formation by Escherichia coli O157:H7 and Ralstonia spp Authors
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: March 18, 2013
Publication Date: N/A
Technical Abstract: Introduction: Ralstonia spp., a heterotrophic bacterium that are isolated from produce processing environments as part of the native microflora, have strong potentials for formaing biofilms on various surfaces. When co-cultured, Escherichia coli O157:H7 (EcO157) and Ralstonia spp. displayed a synergistic interaction in dual-species biofilms formation, as indicated by the increased biomass in the biofilms. It is hypothesized that the presence of strong biofilm forming microfolora such as Ralstonia spp. could potentially enhance the survival of EcO157 in harsh environment. Purpose: This study was conducted to examine the potential factors that affected this synergistic interaction. Methods: The ability of EcO157 attaching to solid surfaces was examined using tissue culture plates in the presence or absence of Ralstonia spp. A drip flow biofilm reactor was used to examine the development of dual-species biofilm over time. EcO157 strain EDL933 and mutants deficient in curli production were also tested for dual-species biofilm formation with Ralstonia spp. Cells in biofilms were enumerated by plating and biofilm structure was examined using confocal laser scanning microscopy (CLSM). Results: The presence of pre-formed Ralstonia spp. biofilms significantly enhanced the attachment of EcO157 on solid surfaces. Within 4 hrs of inoculation, attachment by EcO157 on tissue culture plate with pre-formed Ralstonia biofilm increased by 0.83 log CFU/cm2 compared to that on a plain plate. This enhanced initial attachment of EcO157 was not observed when it was co-inoculated with Ralstonia spp., indicating the importance of the preformed Ralstonia spp. biofilm in this interaction. While co-culturing of EcO157 and Ralstonia spp. significantly increased the incorporation of EC O157 in the dual species biofilms after 24 hrs, this increase was not observed when curli deficient strains ('csgA and 'csgD) was used, suggesting that the increase of EcO157 in biofilm was associated with curli production. Microscopic examination of the dual species biofilm using CLSM showed a unique arrangement of the two strains, where EcO157 microcolones were often encapsulated by Ralstonia spp. on the solid substrate. Significance: This study provided evidence that biofilm formation by native microflora promotes the survival of foodborne pathogens such as EcO157 through a synergistic interaction.