Submitted to: International Journal of Environment and Pollution
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/28/2011
Publication Date: 12/1/2011
Citation: Pachepsky, Y.A., Garzio-Hadzick, A., Shelton, D.R., Hadzick, Z., Hull, R. 2011. Survival of E. coli O157:H12 in creek sediments after inoculation and re-inoculation. International Journal of Environment and Pollution. 46:234-245. Interpretive Summary: Bottom sediments of streams and lakes are known to harbor large populations of microorganisms, including pathogens and indicators of fecal contamination. Resuspension of sediments can drastically change the microbiological quality of the water column and affect its suitability for irrigation and recreational purposes. Since sediments are not the primary habitat for E. coli, it is not currently known how and why populations in bottom sediments can persist for months in these conditions; whereas in laboratory experiments E. coli populations in sediments decrease by one to four orders of magnitude after one month of incubation. We tested the hypothesis that inactivation of E. coli (using a specific strain) in sediment would be slower after re-inoculation as compared to the original inoculation, i.e. the strain could adapt to the sediment environment after the original inoculation. The inoculation and re-inoculation of both sandy and clayey sediments showed that indeed the die-off rates were statistically significantly slower after re-inoculation, although the differences in rates were relatively small. We also observed a substantial increase in E. coli strain populations both after inoculation and re-inoculation. These results indicate that a fresh supply of nutrients is necessary to keep the high E. coli population in sediments. Results of this work will be useful to engineers and biologists working in the area of surface water quality to develop a conceptual understanding, and eventually predictive models, of the effect of sediment microorganism populations on microbiological water quality.
Technical Abstract: Aims: The objective of this work was to test the hypothesis that the E. coli inactivation rates after streambed sediment inoculation do not differ significantly from the inactivation rates in the same sediment after re-inoculation, and to elucidate the relative importance of nutrient availability and E. coli adaptation to sediment environment. Methods and results: The hypothesis was tested for the E. coli O157:H12 strain with two sediments with markedly different particle size distributions and organic matter contents in one-month-long experiments in flow-through chambers at 14º and 24º C. The inactivation in sediments was controlled by temperature and sediment composition. The exponential inactivation stage started on day 4 in both inoculation experiments. The inactivation rates after re-inoculation were slightly smaller than after inoculation. Conclusions: This study suggests that (a) nutrient availability did not change after a month of E. coli strain die-off in submerged sediment, and (b) that E. coli strain was able to adapt to the sediment environment so that its survival after re-inoculation somewhat improved. Significance and Impact of the Study: Survival of E. coli in stream bed sediment can be, as the first approximation and in short term, viewed as a phenomenon controlled by temperature, sediment composition, nutrient level and new inoculations