Genomic characterization of enterohaemolysin-encoding haemolytic Escherichia coli of animal and human origin

Abstract

Enterohaemolysin (Ehx) and alpha-haemolysin are virulence-associated factors (VAFs) causing the haemolytic phenotype in <i>Escherichia coli</i>. It has been shown that chromosomally and plasmid-encoded alpha-haemolysin are characteristic of specific pathotypes, virulence-associated factors and hosts. However, the prevalence of alpha- and enterohaemolysin does not overlap in the majority of pathotypes. Therefore, this study focuses on the characterization of the haemolytic <i>E. coli</i> population associated with multiple pathotypes in human and animal infectious diseases. Using a genomics approach, we investigated characteristic features of the enterohaemolysin-encoding strains to identify factors differentiating enterohaemolysin-positive from alpha-haemolysin-positive <i>E. coli</i> populations. To shed light on the functionality of Ehx subtypes, we analysed Ehx-coding genes and inferred EhxA phylogeny. The two haemolysins are associated with a different repertoire of adhesins, iron acquisition or toxin systems. Alpha-haemolysin is predominantly found in uropathogenic <i>E. coli</i> (UPEC) and predicted to be chromosomally encoded, or nonpathogenic and undetermined <i>E. coli</i> pathotypes and typically predicted to be plasmid-encoded. Enterohaemolysin is mainly associated with Shiga toxin-producing <i>E. coli</i> (STEC) and enterohaemorrhagic <i>E. coli</i> (EHEC) and predicted to be plasmid-encoded. Both types of haemolysin are found in atypical enteropathogenic <i>E. coli</i> (aEPEC). Moreover, we identified a new EhxA subtype present exclusively in genomes with VAFs characteristic of nonpathogenic <i>E. coli</i>. This study reveals a complex relationship between haemolytic <i>E. coli</i> of diverse pathotypes, providing a framework for understanding the potential role of haemolysin in pathogenesis.