|LIU, NANCY - University Of Maryland|
|LO, Y. MARTIN - University Of Maryland|
Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2014
Publication Date: 1/1/2015
Citation: Liu, N.T., Nou, X., Bauchan, G.R., Murphy, C.F., Lefcourt, A.M., Shelton, D.R., Lo, Y. 2015. Effects of environmental parameters on the dual-species biofilms formed by Escherichia coli O157:H7 and Ralstonia insidiosa, a strong biofilm producer isolated from a fresh-cut processing plant. International Journal of Food Microbiology. 78:121-127.
Interpretive Summary: Biofilm formation is an important mechanism for bacterial survival in stressful environments. They can form on the surface of fresh produce processing equipment, making it harder to disinfect. We previously showed that pathogenic E. coli O157 strains with low biofilm formation ability could interact with Ralstonia insidiosa, a strain commonly found on fresh produce and able to form strong biofilms, to create multispecies biofilms. This study demonstrated that the formation of such multispecies biofilms were not significantly impacted by incubation temperature or by the availability of nutrients in the growth media. Microscopic examination showed that in the mature dual species biofilms, the two species were spatially segregated in such a way that the E. coli O157 cells were protected by those of R. insidiosa. This finding suggests that extra care may be required in the disinfection of fresh produce processing equipment. These results will of interest to other scientists, regulators and food processors.
Technical Abstract: 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 coli O157:H7 into dual-species biofilms. In this study, interactions between E. coli O157:H7 and R. insidiosa were examined under different incubating conditions. Under static culture conditions, the incorporation of E. coli O157:H7 into biofilms with R. insidiosa was not significantly affected by either low incubating temperature (10 oC) or by limited nutrient availability. Greater enhancement of E. coli O157:H7 incorporation in dual-species biofilms was observed using a continuous culture system with limited nutrient availability. Under the continuous culture conditions used in this study, E coli O157:H7 cells showed a strong tendency of co-localizing with R. insidiosa on glass surface at the early stage of biofilm formation. As the biofilms matured, E coli O157:H7 were mostly found at the bottom layer of the dual species biofilms, suggesting an effective protection by R. insidiosa in the mature biofilms.