Core and Accessory Genome Comparison of Australian and International Strains of O157 Shiga Toxin-Producing Escherichia coli - PubMed
- ️Wed Jan 01 2020
Core and Accessory Genome Comparison of Australian and International Strains of O157 Shiga Toxin-Producing Escherichia coli
Alexander Pintara et al. Front Microbiol. 2020.
Abstract
Shiga toxin-producing Escherichia coli (STEC) is a foodborne pathogen, and serotype O157:H7 is typically associated with severe disease. Australian STEC epidemiology differs from many other countries, as severe outbreaks and HUS cases appear to be more often associated with non-O157 serogroups. It is not known why Australian strains of O157 STEC might differ in virulence to international strains. Here we investigate the reduced virulence of Australian strains. Multiple genetic analyses were performed, including SNP-typing, to compare the core genomes of the Australian to the international isolates, and accessory genome analysis to determine any significant differences in gene presence/absence that could be associated with their phenotypic differences in virulence. The most distinct difference between the isolates was the absence of the stx2a gene in all Australian isolates, with few other notable differences observed in the core and accessory genomes of the O157 STEC isolates analyzed in this study. The presence of stx1a in most Australian isolates was another notable observation. Acquisition of stx2a seems to coincide with the emergence of highly pathogenic STEC. Due to the lack of other notable genotypic differences observed between Australian and international isolates characterized as highly pathogenic, this may be further evidence that the absence of stx2a in Australian O157 STEC could be a significant characteristic defining its mild virulence. Further work investigating the driving force(s) behind Stx prophage loss and acquisition is needed to determine if this potential exists in Australian O157 isolates.
Keywords: Australia; O157; STEC; epidemiology; genomics.
Copyright © 2020 Pintara, Jennison, Rathnayake, Mellor and Huygens.
Figures

Hierarchal cluster tree of serogroup O157 STEC genomes based on the Jaccard distance of SNP differences identified by mapping all isolates to the AUSMDU00002545 genome as a reference. Asterisk indicates bootstrap support of >95%. Isolates labeled in yellow are Australian, isolates in blue are international, and isolates in red are associated with the United Kingdom 2015 outbreak. Indicated to the right of the tree are; the subtype of both the A and B subunits of the Shiga toxin genes, purple for stx1a, green for stx2a, and red for stx2c; whether the isolates were clinically isolated (dark gray), or from cattle (light gray); and whether the isolates carry the single cytosine base inserted at 125 nt of the flgF gene, indicated by the presence of a plus sign.

Hierarchal cluster tree as shown in Figure 1, highlighting the Australian clinical isolates in red and United Kingdom outbreak isolates in blue. Below the tree is a heatmap indicating the presence (green) and absence (red) of genes reported to be associated with virulence in STEC. The virulence genes have been categorized into difference pathogenic processes involved in STEC pathogenesis.

Hierarchal cluster tree as shown in Figure 1, highlighting the Australian clinical isolates in red and United Kingdom outbreak isolates in blue. Below the tree is a heatmap indicating the presence (green) and absence (red) of accessory genes found to be significantly different in their presence and absence between Australian clinical and United Kingdom outbreak isolates.
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