Comparative genomic analysis of Escherichia coli 0157:H7 isolated from super-shedder and low-shedder cattle

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Munns, Krysty D.
Zaheer, Rahat
Xu, Yong
Stanford, Kim
Laing, Chad R.
Gannon, Victor P. J.
Selinger, L. Brent
McAllister, Tim A.
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Public Library of Science
Cattle are the primary reservoir of the foodborne pathogen Escherichia coli O157:H7, with the concentration and frequency of E. coli O157:H7 shedding varying substantially among individual hosts. The term ‘‘super-shedder” has been applied to cattle that shed 104 cfu E. coli O157:H7/g of feces. Super-shedders have been reported to be responsible for the majority of E. coli O157:H7 shed into the environment. The objective of this study was to determine if there are phenotypic and/or genotypic differences between E. coli O157:H7 isolates obtained from super-shedder compared to low-shedder cattle. From a total of 784 isolates, four were selected from low-shedder steers and six isolates from super-shedder steers (4.01–8.45 log cfu/g feces) for whole genome sequencing. Isolates were phage and clade typed, screened for substrate utilization, pH sensitivity, virulence gene profiles and Stx bacteriophage insertion (SBI) sites. A range of 89–2473 total single nucleotide polymorphisms (SNPs) were identified when sequenced strains were compared to E. coli O157:H7 strain Sakai. More non-synonymous SNP mutations were observed in low-shedder isolates. Pan-genomic and SNPs comparisons did not identify genetic segregation between supershedder or low-shedder isolates. All super-shedder isolates and 3 of 4 of low-shedder isolates were typed as phage type 14a, SBI cluster 3 and SNP clade 2. Super-shedder isolates displayed increased utilization of galactitol, thymidine and 3-O-β-D-galactopyranosyl-Darabinose when compared to low-shedder isolates, but no differences in SNPs were observed in genes encoding for proteins involved in the metabolism of these substrates. While genetic traits specific to super-shedder isolates were not identified in this study, differences in the level of gene expression or genes of unknown function may still contribute to some strains of E. coli 0157:H7 reaching high densities within bovine feces.
Sherpa Romeo green journal; open access
Escherichia coli 0157:H7 , E. coli , Super-shedder cattle , Low-shedder cattle , Cattle -- Feces
Munns, K. D., Zaheer, R., Xu, Yohg, Stanford, K., Laing, C. R., Gannon, V. P. J., ... McAllister, T. A. (2016). Comparative genomic analysis of Escherichia coli 0157:H7 isolated from super-shedder and low-shedder cattle. PLoS ONE, 11(3), e0151673. doi:10.1371/journal.pone.0151673