Factors contributing to biofilm formation of Yersinia enterocolitica : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology, Massey University, Palmerston North, New Zealand

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Biofilms of pathogenic bacteria are recognised as a threat to food safety. The aim of the present study was to investigate the potential of Yersinia enterocolitica to form biofilms in the pork processing environment and identify the resistance of these biofilms to sanitation. The biofilm formation by Y. enterocolitica was monitored at conditions simulating pork processing environment under daily cleaning routine using an impedance method established in this study. Results showed that Y. enterocolitica had the potential to form biofilm and become resistant to sanitation in a pork processing environment. An investigation into the factors influencing biofilm formation of Y. enterocolitica indicated that the Ca2+ ion increased the level of biofilm formation. In addition, the presence of the virulence plasmid pYV is essential for the biofilm Ca2+ response. Further analysis of the bacterial cell surface properties and extracellular polymeric substance (EPS) composition suggested that the pYV+ cell surfaces are more negatively charged and more hydrophobic than the pYV- cells although no significant difference was observed with the addition of Ca2+. The pYV+ cells appear to produce more exopolysaccharide than the pYV- cells regardless of Ca2+ concentration. Ca2+ was able to increase the yield of extracellular DNA while the presence of pYV appeared to be dispensable in terms of extracellular DNA release. Analysis of cell wall protein revealed one protein expressed in the pYV+ cells but absent in the pYV- cells.
Content removed from thesis for copyright reasons: Wang H., Palmer J., & Flint S. (2015). A rapid method for the nonselective enumeration of Yersinia enterocolitica, a foodborne pathogen associated with pork. Meat Science, 113: 59–61. doi:10.1016/j.meatsci.2015.11.005; Wang H., Tay M., Palmer J., Flint S. (2016) Biofilm formation of Yersinia enterocolitica and its persistence following treatment with different sanitation agents. Food Control, 73, 433-437. doi:10.1016/j.foodcont.2016.08.033
Yersinia enterocolitica, Biofilms, Pork, Microbiology, Research Subject Categories::TECHNOLOGY::Chemical engineering::Food technology