On the Transport of Viable but Non-Culturable (VBNC) E.coli O157:H7 in Soil and Groundwater

The influence of the viable but non-culturable (VBNC) state on the expression of specific phenotypic traits of Enterohemorrhagic Escherichia coli O157:H7 as well as its transport behaviour in porous media has been examined in this study. E.coli O157:H7 is a human pathogen capable of entering a viable but non-culturable (VBNC) state following exposure to sublethal stress. In the VBNC state, E.coli O157:H7 is not detectable by standard culture techniques, yet is able to retain its virulence and ability to cause illness in humans. To date there is no in-depth information regarding the transport of VBNC E.coli species in soil or groundwater. Due to the public health risk, it becomes important to examine whether discrepancies exist between the transport behaviors of culturable and VBNC E.coli O157:H7 to help decide if current protocols for detecting this pathogen are accurate. This study identifies and contrasts transport-related properties of the two cell stages including hydrophobicity, extracellular polymeric substance (EPS) composition, and cell widths/lengths. Transport behaviors of the two cellular states are quantified and compared using column transport assays. Our results show that when E.coli O157:H7 cells enter into the VBNC state, there is an accompanied decrease in the hydrophobicity of the cells, shrinking of the cell profile from rod-shaped to coccoid, as well as a significant increase in tightly-bound surface proteins and sugars. Transport assays revealed a notable increase in mass flux when cells were in the VBNC state versus the culturable state. This research will contribute to the current knowledge-base describing E.coli O157:H7 cells in the VBNC state, spark dialogue concerning the accuracy of currently-used identification protocols, as well as add further evidence to the notion that bacteria transport in the subsurface is a truly dynamic process.