Survival of various ERIC-genotypes of Shiga toxin-producing Escherichia coli in well water

Abstract

Recently, there has been a surge of interest in understanding the survival of Shiga toxinproducing Escherichia coli (STEC) in aquatic environments. Fifteen strains of STEC were monitored, individually, in untreated well water samples incubated at 10 and 22 • C for 56 days. The strains were selected from three serogroups (O26, Ol11 and O157) and represented five distinct ERIC (enterobacterial repetitive intergenic concensus)-genotypes. The microcosms were prepared in triplicate and inoculated at an initial cell density of about 7.0 log CFU/ml well water. At 10 • C, the cell density of five STEC strains fell below the detection limit of 0.8 log CFU/ml by day 56. Of the ten persisting strains, four showed superior survival with cell densities decreasing to an average of about 5 log CFU/ml while the remaining six strains showed moderate levels of survival, decreasing to an average cell density of about 3 log CFU/ml. At 22 • C, strain H32 (genotype I) and H15 (genotype B) persisted at 1.1 log CFU/ml and 2.2 log CFU/ml in 56 days, respectively. The other 13 STEC strains dropped below the detection limit between weeks 3 to 8. The 15 strains demonstrated highly variable levels of survival with no correlation between ERIC-genotypes or serogroups and the strains' ability to persist in the well water samples. Although strain H32 (O157:H7) persisted significantly longer than strain H22 (O157:H7) in natural well water at both 10 and 22 • C, both strains survived equally well in sterile well water, indicating that individual STEC strains vary in their ability to compete with background microbial populations.

Role of rpoS in Escherichia coli O157:H7 Strain H32 Biofilm Development and Survival

“…4). These findings are consistent with studies revealing that planktonic E. coli O157:H7 has better survival in autoclaved water and sterile filtered water than in untreated lake and well water (3,52,54). Predictably, decreased overall survival results from additive stress, where competition and predation from indigenous flora resulted in more significant reductions in E. coli O157:H7 than did the comparative nutrient deprivation in filter-sterilized lake water and both nutrient deprivation and osmotic stress in distilled water.…”

“…Of concern is the survival of pathogenic E. coli for extended periods of time under the comparatively nutrient-deprived conditions of untreated well water, bottled water, municipal drinking water, natural water bodies, and water distribution systems (24,52,53,54). As such, further investigation into the role of rpoS in the survival of E. coli O157:H7 biofilm cells in both natural and treated water samples is required.…”

Effect of Stress on Non-O157 Shiga Toxin–Producing Escherichia coli

“…Watterworth (56) indicate that 026:H11 and 0111:H8 survival in well water is similar to that of 0157:H7. The Shiga toxin gene (stx2) was detected in non-0157 STEC (not further identified) from Argentinian recreational waters (38).…”

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

“…The survival of E. coli O157:H7 in water [14], [15], [16], [17], [18], [19], manure and manure slurry [20], [21], [22], manure-amended soil [23], [24], [25], and sediment [26], [27], is well documented with sporadic reports in natural soils [28], [29]. More direct results could be obtained by applying pathogenic strain in the survival experiments [30], however, most of the studies used nonpathogenic E. coli O157:H7 strains [22], [24], [31], [32] due to environmental safety and regulations.…”