Abstract
Escherichia coli O103, harbored in the hindgut and shed in the feces of cattle, can be enterohemorrhagic (EHEC), enteropathogenic (EPEC), or putative non-pathotype. The genetic diversity particularly that of virulence gene profiles within O103 serogroup is likely to be broad, considering the wide range in severity of illness. However, virulence descriptions of the E. coli O103 strains isolated from cattle feces have been primarily limited to major genes, such as Shiga toxin and intimin genes. Less is known about the frequency at which other virulence genes exist or about genes associated with the mobile genetic elements of E. coli O103 pathotypes. Our objective was to utilize whole genome sequencing (WGS) to identify and compare major and putative virulence genes of EHEC O103 (positive for Shiga toxin gene, stx1, and intimin gene, eae; n = 43), EPEC O103 (negative for stx1 and positive for eae; n = 13) and putative non-pathotype O103 strains (negative for stx and eae; n = 13) isolated from cattle feces. Six strains of EHEC O103 from human clinical cases were also included. All bovine EHEC strains (43/43) and a majority of EPEC (12/13) and putative non-pathotype strains (12/13) were O103:H2 serotype. Both bovine and human EHEC strains had significantly larger average genome sizes (P < 0.0001) and were positive for a higher number of adherence and toxin-based virulence genes and genes on mobile elements (prophages, transposable elements, and plasmids) than EPEC or putative non-pathotype strains. The genome size of the three pathotypes positively correlated (R2 = 0.7) with the number of genes carried on mobile genetic elements. Bovine strains clustered phylogenetically by pathotypes, which differed in several key virulence genes. The diversity of E. coli O103 pathotypes shed in cattle feces is likely reflective of the acquisition or loss of virulence genes carried on mobile genetic elements.
Highlights
Enterohemorrhagic Escherichia coli (EHEC) carry one or both phage-encoded Shiga toxin genes and the attaching and effacing gene, which is harbored in the chromosomal-encoded locus of enterocyte effacement (LEE) pathogenicity island
Sixty-nine bovine O103 strains, that belonged to three subgroups, EHEC (n = 43), enteropathogenic Escherichia coli (EPEC) (n = 13) and putative non-pathotype (n = 13) and six human clinical EHEC O103 strains were included in the study
The in silico analysis performed here does not provide phenotypic evidence of virulence contributions, a number of major and putative virulence genes were comparable among bovine and human EHEC O103 strains, which may indicate the potential for bovine EHEC O103 to cause human infection
Summary
Enterohemorrhagic Escherichia coli (EHEC) carry one or both phage-encoded Shiga toxin genes (stx and stx2) and the attaching and effacing gene (eae), which is harbored in the chromosomal-encoded locus of enterocyte effacement (LEE) pathogenicity island. Enteropathogenic E. coli (EPEC), including EPEC O103, do not carry stx genes; they possess eae and other virulence genes to cause attaching and effacing lesions that can result in mild to severe diarrhea, or even death, in children [7, 8]. The loss of the stx gene(s), a frequently reported event [10, 11], can transform an EHEC into an EPEC pathotype. These major pathotype-defining mobile virulence genes have been well studied, but less is known about how other mobile elements contribute to the overall virulence diversity in O103 serogroup. We hypothesize that the diversity of O103 pathotypes harbored and shed in the feces of cattle is reflective of the loss or acquisition of genes carried on mobile genetic elements
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