Escherichia coli O157 survival in liquid culture and artificial soil microcosms with variable pH, humic acid and clay content

Aims This research was performed to investigate the influence of clay and humic acid on Escherichia coli O157 survival in model soils. Additionally, the influence of pH and humic acid on E. coli O157 in liquid culture was investigated. Methods and Results Artificial soil microcosms were prepared with sand, kaolinite, bentonite and humic acid. Artificial soil microcosms pH was adjusted (6·0–7·0) with aluminium sulphate before E. coli O157 inoculation. After 56 days of incubation at 30°C, significant differences in E. coli O157 log CFU per gram were observed between 0 and 1000 ppm (P < 0·0001) and 0 and 5000 ppm (P < 0·0001) humic acid in 1·5% clay soils, but not in 7·5 or 15% clay soils. Significant differences (P < 0·05) in E. coli O157 log CFU per ml were observed in liquid culture influenced by humic acid concentrations after 8 h at 37°C. Conclusions The developed model soils support E. coli O157 populations over 28 days, and higher clay soils may aid in E. coli O157 survival. Significance and Impact of the Study These results provide insights into physicochemical properties of soil that may influence E. coli O157 in the environment and help explain E. coli O157 survival in various soils and geographical regions.