Abstract
Background:Differences betweenEscherichia coliO157 (O157) strains are well-established with some of these strains being associated with major outbreaks in the US. EDL933 is one such O157 strain that caused a multistate outbreak in 1982 and has since been used as a prototype in various O157-related experiments.Objective:As O157 can readily acquire genetic mutations, we sought to determine if the genetic and phenotypic profiles of EDL933 strains from different sources would be consistent.Methods:We evaluated wild-type O157 strains stocked as EDL933 from three different laboratories, in the strain typing Polymorphic Amplified Typing Sequence (PATS) and the bovine rectal-anal junction squamous epithelial (RSE) cell- and HEp-2 cell- adherence assays. In addition, we also verified if Shiga toxins (Stx), the Locus of Enterocyte Effacement (LEE) or curli fimbriae contributed to the adherence phenotypes observed using mutant and wild-type EDL933 isolates.Results:Our results showed differences in PATS profiles and RSE cell-adherence phenotype, with no influence from the Stx or LEE genes, between EDL933 from different sources. Interestingly, the EDL933 strain that demonstrated the most contrasting diffuse adherence phenotype on RSE cells, EDL933-T, had decreased curli production that may have contributed to this phenotype.Conclusion:Our observations suggest that a comprehensive characterization of bacterial isolates, even if assigned to the same strain type prior to use in experiments, is warranted to ensure consistency and reproducibility of results.
Highlights
The O157 strain EDL933 WT American Type Culture Collection (ATCC) 43895 with the four virulence genes stx1, stx2, eae, and hlyA, the O157 strain 86-24 lacking the stx1 gene, and the avirulent E. coli K-12 lacking all the virulence genes along with some of the genetic regions in the O157 genome were included as comparative controls in the Polymorphic Amplified Typing Sequence (PATS) assay (Table 2) [53]
No definite correlation between the PATS-based genotype and the differences in the rectal-anal junction squamous epithelial (RSE) cell adherence phenotype could be established, but the experiments with the isogenic mutants established that Shiga toxins (Stx) and Locus of Enterocyte Effacement (LEE) did not play a role in the adherence phenotypes
Our results demonstrate that the EDL933 strains of O157, obtained from different sources, can exhibit varied genetic and adherence profiles on eukaryotic cells (Table 2 and Table S1)
Summary
Enterohemorrhagic Escherichia coli (EHEC) O157:H7 (O157) is a well-known Shiga toxin-producing E. coli (STEC). Worldwide outbreaks of E. coli O157:H7 (O157) [2] have been reoccurring ever-since the O157 strain EDL933, banked with the American Type Culture Collection (ATCC 43895), was first isolated from a 1982 food-borne outbreak in the US [9 - 11]. Cattle are the major reservoirs for O157, which tend to persist at the bovine intestinal recto-anal junction (RAJ), especially at the follicle-associated-epithelial (FAE) cells of the RAJ using the LEE-encoded intimin [6, 14 - 19]. Differences between Escherichia coli O157 (O157) strains are well-established with some of these strains being associated with major outbreaks in the US. EDL933 is one such O157 strain that caused a multistate outbreak in 1982 and has since been used as a prototype in various O157-related experiments
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