Q-232. Growth and Survival of Escherichia coli O157:H7 in Soil Organic Matter

A. Christie1, S. Vilain1, B. Voigt2, S. Gibson1, D. Francis1, M. Hecker2, V. S. Brozel1;
1South Dakota State Univ., Brookings, SD, 2Ernst Moritz Arndt Univ., Greifswald, GERMANY.

Food products are required to be free from enterohaemorrhagic E. coli O157:H7 but despite various measures taken during processing, consumers can still be exposed to this pathogen. The ecophysiology of this bacterium is inadequately understood, with several analyses indicating soil as an underestimated reservoir. We hypothesized that E. coli 0157:H7 is able to grow using the soluble nutrients in soil, and that growth under these conditions would affect survival of the ensuing populations. Liquid extract of soil, Soil Extractable Soluble Organic Matter (SESOM) was prepared using various soils. Extracts were filtered to sterility to avoid chemical modification by heat. E. coli 0157:H7 strain 933D (stxII-) was incubated while shaking at 30 ºC in the various SESOM, with LB as the control. Growth and survival were determined by optical density and culturable counting for 18d, and periodic fluorescence microscopy of BacLight-stained samples. Biomass for proteomic analysis was harvested in mid-exponential and late stationary phase (d3) and proteins were resolved by two-dimensional electrophoresis. Gel images were analyzed using PDQuest and spots of interest were identified by MALDI-TOF-MS-MS. Proteome maps were compared by principal component analysis (PCA). E. coli 0157:H7 was able to grow exponentially in the various SESOM. In contrast to LB-grown populations, SESOM populations did not loose culturability during the 18d experimental period. The proteomic data indicated a substantial physiological switch in SESOM-grown cells. Stationary SESOM populations appeared closer to exponential than to stationary phase LB populations. Proteome differences included a shift from OmpC to OmpF, lower levels of stress proteins (AhpC, Slp, UspA and OsmY) and shifts in membrane- and wall - synthesizing components. SESOM populations also produced enhanced amounts of the antibiotic peptide MccB17. These results indicate soils as a potential reservoir of enteric pathogens such as E. coli 0157:H7 by supporting their growth and survival. Thus soils can be a source for contamination of agricultural products.