Survival ofEscherichia coliO157 in autoclaved and natural sandy soil mesocosms

While the soil microbiome may influence pathogen survival, determining the major contributors that reduce pathogen survival is inconclusive. This research was performed to determine the survival ofE.coliO157 in autoclaved and natural (unautoclaved) sandy soils. Soils were inoculated with three differentE.coliO157 strains (stx1+/stx2+,stx1-/stx2-,and stx1-/stx2+), and enumerated until extinction at 30 degrees C. There was a significant difference in the survival ofE.coliO157 based on soil treatment (autoclaved versus natural) at 30 degrees C on days 1 (P= 0.00022), 3, (P= 2.53e-14), 7 (P= 5.59e-16), 14 (P= 1.072e-12), 30 (P= 7.18e-9), and 56 (P= 0.00029), with greater survival in autoclaved soils. The time to extinction (two consecutive negative enrichments) for all three strains was 169 and 84 days for autoclaved and natural soils, respectively. A separateE.coliO157 trial supplemented with 16S rRNA gene sequencing of the soil microbiome was performed at 15 degrees C and 30 degrees C on days 0, 7, 14, and 28 for each soil treatment. Greater species richness (Chao1,P= 2.2e-16) and diversity (Shannon,P= 2.2e-16) was observed in natural soils in comparison with autoclaved soils. Weighted UniFrac (beta-diversity) showed a clear distinction between soil treatments (P= 0.001). The greatest reduction ofE.coliO157 was observed in natural soils at 30 degrees C, and several bacterial taxa positively correlated (relative abundance) with time (day 0 to 28) in these soils (P< 0.05), suggesting that the presence of those bacteria might cause the reduction ofE.coliO157. Taken together, a clear distinction inE.coliO157 survival, was observed between autoclaved and natural soils along with corresponding differences in microbial diversity in soil treatments. This research provides further insights into the bacterial taxa that may influenceE.coliO157 in soils.