title: Comparative Genomics and Characterization of Hybrid Shigatoxigenic and Enterotoxigenic Escherichia coli (STEC/ETEC) Strains.
abstract: BACKGROUND
  Shigatoxigenic Escherichia coli (STEC) and enterotoxigenic E. coli (ETEC) cause serious foodborne infections in humans. These two pathogroups are defined based on the pathogroup-associated virulence genes: stx encoding Shiga toxin (Stx) for STEC and elt encoding heat-labile and/or est encoding heat-stable enterotoxin (ST) for ETEC. The study investigated the genomics of STEC/ETEC hybrid strains to determine their phylogenetic position among E. coli and to define the virulence genes they harbor.
  
  
  METHODS
  The whole genomes of three STEC/ETEC strains possessing both stx and est genes were sequenced using PacBio RS sequencer. Two of the strains were isolated from the patients, one with hemolytic uremic syndrome, and one with diarrhea. The third strain was of bovine origin. Core genome analysis of the shared chromosomal genes and comparison with E. coli and Shigella spp. reference genomes was performed to determine the phylogenetic position of the STEC/ETEC strains. In addition, a set of virulence genes and ETEC colonization factors were extracted from the genomes. The production of Stx and ST were studied.
  
  
  RESULTS
  The human STEC/ETEC strains clustered with strains representing ETEC, STEC, enteroaggregative E. coli, and commensal and laboratory-adapted E. coli. However, the bovine STEC/ETEC strain formed a remote cluster with two STECs of bovine origin. All three STEC/ETEC strains harbored several other virulence genes, apart from stx and est, and lacked ETEC colonization factors. Two STEC/ETEC strains produced both toxins and one strain Stx only.
  
  
  CONCLUSIONS
  This study shows that pathogroup-associated virulence genes of different E. coli can co-exist in strains originating from different phylogenetic lineages. The possibility of virulence genes to be associated with several E. coli pathogroups should be taken into account in strain typing and in epidemiological surveillance. Development of novel hybrid E. coli strains may cause a new public health risk, which challenges the traditional diagnostics of E. coli infections.
authors: Bacterial Infections Unit, Department of Infectious Diseases, National Institute for Health and Welfare (THL), Helsinki, Finland.
authors: Outi
authors: O
authors: Nyholm
authors: Bacterial Infections Unit, Department of Infectious Diseases, National Institute for Health and Welfare (THL), Helsinki, Finland.
authors: Jani
authors: J
authors: Halkilahti
authors: Department of Microbiology and Immunology, University of Gothenburg, Gothenburg, Sweden.
authors: Gudrun
authors: G
authors: Wiklund
authors: Institute of Biotechnology, University of Helsinki, Helsinki, Finland.
authors: Uche
authors: U
authors: Okeke
authors: Institute of Biotechnology, University of Helsinki, Helsinki, Finland.
authors: Lars
authors: L
authors: Paulin
authors: Institute of Biotechnology, University of Helsinki, Helsinki, Finland.
authors: Petri
authors: P
authors: Auvinen
authors: Bacterial Infections Unit, Department of Infectious Diseases, National Institute for Health and Welfare (THL), Helsinki, Finland; Department of Food and Environmental Sciences, University of Helsinki, Helsinki, Finland.
authors: Kaisa
authors: K
authors: Haukka
authors: Bacterial Infections Unit, Department of Infectious Diseases, National Institute for Health and Welfare (THL), Helsinki, Finland.
authors: Anja
authors: A
authors: Siitonen
mesh_terms: D000818:Animals; D002417:Cattle; D054307:Enterotoxigenic Escherichia coli / Q000235:genetics / Q000302:isolation & purification* / Q000472:pathogenicity; D004927:Escherichia coli Infections / Q000235:genetics / Q000382:microbiology*; D016680:Genome, Bacterial; D023281:Genomics / Q000379:methods*; D006801:Humans; D054323:Shiga-Toxigenic Escherichia coli / Q000235:genetics / Q000302:isolation & purification* / Q000472:pathogenicity; D014774:Virulence / Q000235:genetics; D037521:Virulence Factors / Q000235:genetics*
chemical_list: D037521:Virulence Factors