Title: Incorporation of Escherichia coli O157:H7 in biofilms with Ralstonia insidiosa, a primary localizer for the development of heterogeneous biofilms Authors
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: April 6, 2013
Publication Date: April 10, 2013
Citation: Liu, N.T., Nou, X., Lefcourt, A.M., Shelton, D.R., Lo, Y.M. 2013. Incorporation of Escherichia coli O157:H7 in biofilms with Ralstonia insidiosa, a primary localizer for the development of heterogeneous biofilms. [abstract]. Technical Abstract: It is hypothesized that the presence of strong biofilm forming microflora could potentially enhance the survival of Escherichia coli O157:H7 (EcO157) in harsh environment. In this study, a strong biofilm forming bacterium, Ralstonia insidiosa, previously isolated from a fresh-cut produce plant was co-cultured with an Escherichia coli O157:H7 strain (EcO157, a weak biofilm former) to allow examination of the formation of dual-species biofilms at 30 and 10 oC. Biofilm-forming capability was determined by a crystal violet binding assay, whereas microbial growth was monitored by TSA total plate count. A “synergistic” effect was observed in biofilm formation when R. insidiosa and EcO157 were co-cultured at 30 oC in 10% TSB, as evidenced by an increase in biomass. Fluorescent microscopic images revealed a significant thickening (p<0.05) of the biofilm formed in the presence of both bacteria when compared to the biofilm formed by R. insidiosa in mono-culture. There was a significant increase of EcO157 growth (6.80±0.32 CFU/cm2) in dual-species biofilms when compared to the mono-culture (5.19±0.19 CFU/cm2), which did not form discernible biofilm under conditions tested. Results acquired at 10 oC showed that the increase in EcO157 numbers was correlated (P<0.01) to the increasing growth of R. insidiosa in dual-species biofilms. Besides, CLSM images showed a unique arrangement of the two strains, where EcO157 microcolones were often encapsulated by Ralstonia spp. on the solid substrate. These results suggested that microflora native to produce processing plants can potentially enhance the survival of bacterial pathogens such as EcO157 by promoting their incorporation into biofilms under temperature abuse conditions or in microenvironments in plants, and thus it is critical to ensure stringent temperature control in food processing plants to inhibit biofilm formation.