Persistence of Escherichia coli O157:H7 and Its Mutants in Soils

Abstract

The persistence of Shiga toxin-producing E. coli O157:H7 in the environment poses a serious threat to public health. However, the role of Shiga toxins and other virulence factors in the survival of E. coli O157:H7 is poorly defined. The aim of this study was to determine if the virulence factors, stx 1, stx 2, stx 1–2, and eae in E. coli O157:H7 EDL933 play any significant role in the growth of this pathogen in rich media and in soils. Isogenic deletion mutants that were missing one of four virulence factors, stx 1, stx 2, stx 1–2, and eae in E. coli O157:H7 EDL933 were constructed, and their growth in rich media and survival in soils with distinct texture and chemistry were characterized. The survival data were successfully analyzed using Double Weibull model, and the modeling parameters of the mutant strains were not significantly different from those of the wild type. The calculated Td (time needed to reach the detection limit, 100 CFU/g soil) for loamy sand, sandy loam, and silty clay was 32, 80, and 110 days, respectively. It was also found that Td was positively correlated with soil structure (e.g. clay content), and soil chemistry (e.g. total nitrogen, total carbon, and water extractable organic carbon). The results of this study showed that the possession of Shiga toxins and intimin in E. coli O157:H7 might not play any important role in its survival in soils. The double deletion mutant of E. coli O157:H7 (stx 1 − stx 2 −) may be a good substitute to use for the investigation of transport, fate, and survival of E. coli O157:H7 in the environment where the use of pathogenic strains are prohibited by law since the mutants showed the same characteristics in both culture media and environmental samples.

Correlation of Intracellular Trehalose Concentration with Desiccation Resistance of Soil Escherichia coli Populations

“…Soils as secondary habitats of E. coli imply an E. coli life cycle that consists of passage through a host into the environment, adaptation and evolution in the environment, and then passage back into a new host. Such a life cycle would instigate further scientific inquiries about the adaption and evolution of E. coli in natural environments, with particular attention on the emergence of pathogenic E. coli strains (43); for example, E. coli O157:H7 strains have been found to persist in soil for a long period of time (17,28), and some Shiga toxin-producing E. coli (STEC) strains exhibit higher desiccation resistance than nonpathogenic E. coli strains (22), which would also favor their survival in the environment.…”

The General Stress Response Is Conserved in Long-Term Soil-Persistent Strains of Escherichia coli

“…This was done according to the method described by Ma et al (51), with some modifications. Two types of silty loam soils were used for this analysis: soil A (sand, 47%; silt, 52%; clay, Ͻ1%) (pH 7.2) (with total organic carbon, 16.53% of dry solids; total nitrogen, 1.56% of dry solids; C-to-N ratio, 10.6; and organic matter, 31.3%) was collected from Ballyvaughan (53°07=15.6ЉN 9°09=24.8ЉW) in the west of Ireland, and soil B (sand, 43%; silt, 53.9%; clay, 3.1%) (pH 5.19) (with total organic carbon, 4.7%; total nitrogen, 0.35%; C-to-N ratio, 13.43; and organic matter, 9.1%) was collected from Kilfergus (53°07=15.6ЉN 9°09=24.8ЉW) in the midwest of Ireland.…”

Lactococcus lactis Metabolism and Gene Expression during Growth on Plant Tissues

“…All primers used for mutant construction and validation are described in Table S1 in the supplemental material. The upstream flanking region of xylA was PCR amplified using primers A and B and the downstream flanking region of xylA was PCR amplified using primers C and D. Primers B and C contain 5= reverse complementary linker sequences (30) to be used during splicing by overlap extension (SOEing) PCR. The flanking upstream and downstream PCR products were pooled and used as a template for SOEing PCR using primers A and D to link the two original products.…”