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. 2020 Jun 11;15(6):e0234562.
doi: 10.1371/journal.pone.0234562. eCollection 2020.

Survival of Escherichia coli O157 in autoclaved and natural sandy soil mesocosms

Christopher A Baker  1 , Shinyoung Lee  2 , Jaysankar De  1 , Kwangcheol C Jeong  2 , Keith R Schneider  1
Affiliations

Survival of Escherichia coli O157 in autoclaved and natural sandy soil mesocosms

Christopher A Baker et al. PLoS One. .

Abstract

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 of E. coli O157 in autoclaved and natural (unautoclaved) sandy soils. Soils were inoculated with three different E. coli O157 strains (stx1+/stx2+, stx1-/stx2-, and stx1-/stx2+), and enumerated until extinction at 30°C. There was a significant difference in the survival of E. coli O157 based on soil treatment (autoclaved versus natural) at 30°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 separate E. coli O157 trial supplemented with 16S rRNA gene sequencing of the soil microbiome was performed at 15°C and 30°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 of E. coli O157 was observed in natural soils at 30°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 of E. coli O157. Taken together, a clear distinction in E. coli O157 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 influence E. coli O157 in soils.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1
Principal Coordinate Analysis (PCoA) plot based on weighted UniFrac distances for autoclaved (red, n = 32) and natural (blue, n = 31) soil (P = 0.001).
Fig 2
Fig 2. The relative abundance of bacterial taxa (phylum) for natural (Nat) and autoclaved (Auto) soil at 15°C, days 0, 7, 14, 28.
Fig 3
Fig 3. The relative abundance of bacterial taxa (phylum) for natural (Nat) and autoclaved (Auto) soil at 30°C, days 0, 7, 14, 28.
Fig 4
Fig 4
Principal Coordinate Analysis (PCoA) plot based on weighted UniFrac distances for 15°C (red) and 30°C (blue) natural soil on day 28 (P = 0.001).
Fig 5
Fig 5. Bacterial taxa in natural soil at 30°C that positively correlated with time (P < 0.05).
Pearson correlations between relative abundance of bacterial taxa and time (day) were analyzed, and only classified taxa with a relative abundance above 0.05% on day 28 with a significant and positive correlation were included in the heatmap.
See this image and copyright information in PMC

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