title: Allele variants of enterotoxigenic Escherichia coli heat-labile toxin are globally transmitted and associated with colonization factors.
abstract: Enterotoxigenic Escherichia coli (ETEC) is a significant cause of morbidity and mortality in the developing world. ETEC-mediated diarrhea is orchestrated by heat-labile toxin (LT) and heat-stable toxins (STp and STh), acting in concert with a repertoire of more than 25 colonization factors (CFs). LT, the major virulence factor, induces fluid secretion after delivery of a monomeric ADP-ribosylase (LTA) and its pentameric carrier B subunit (LTB). A study of ETEC isolates from humans in Brazil reported the existence of natural LT variants. In the present study, analysis of predicted amino acid sequences showed that the LT amino acid polymorphisms are associated with a geographically and temporally diverse set of 192 clinical ETEC strains and identified 12 novel LT variants. Twenty distinct LT amino acid variants were observed in the globally distributed strains, and phylogenetic analysis showed these to be associated with different CF profiles. Notably, the most prevalent LT1 allele variants were correlated with major ETEC lineages expressing CS1 + CS3 or CS2 + CS3, and the most prevalent LT2 allele variants were correlated with major ETEC lineages expressing CS5 + CS6 or CFA/I. LTB allele variants generally exhibited more-stringent amino acid sequence conservation (2 substitutions identified) than LTA allele variants (22 substitutions identified). The functional impact of LT1 and LT2 polymorphisms on virulence was investigated by measuring total-toxin production, secretion, and stability using GM1-enzyme-linked immunosorbent assays (GM1-ELISA) and in silico protein modeling. Our data show that LT2 strains produce 5-fold more toxin than LT1 strains (P < 0.001), which may suggest greater virulence potential for this genetic variant. Our data suggest that functionally distinct LT-CF variants with increased fitness have persisted during the evolution of ETEC and have spread globally.
authors.affiliation: Department of Microbiology and Immunology, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden Institute of Molecular Biology and Biotechnology, Universidad Mayor de San Andrés, La Paz, Bolivia.
authors.forename: Enrique
authors.initials: E
authors.lastname: Joffré
authors.affiliation: Department of Microbiology and Immunology, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden The Wellcome Trust Sanger Institute, Hinxton, Cambridge, United Kingdom.
authors.forename: Astrid
authors.initials: A
authors.lastname: von Mentzer
authors.affiliation: Pathogen Genomics Laboratory, Computational Bioscience Research Center, King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia.
authors.forename: Moataz
authors.initials: M
authors.lastname: Abd El Ghany
authors.affiliation: Texas Children's Microbiome Center, Department of Pathology and Immunology, Baylor College of Medicine, Houston, Texas, USA.
authors.forename: Numan
authors.initials: N
authors.lastname: Oezguen
authors.affiliation: Texas Children's Microbiome Center, Department of Pathology and Immunology, Baylor College of Medicine, Houston, Texas, USA.
authors.forename: Tor
authors.initials: T
authors.lastname: Savidge
authors.affiliation: The Wellcome Trust Sanger Institute, Hinxton, Cambridge, United Kingdom.
authors.forename: Gordon
authors.initials: G
authors.lastname: Dougan
authors.affiliation: Department of Microbiology and Immunology, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.
authors.forename: Ann-Mari
authors.initials: AM
authors.lastname: Svennerholm
authors.affiliation: Department of Microbiology and Immunology, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, Sweden asa.sjoling@ki.se.
authors.forename: Åsa
authors.initials: Å
authors.lastname: Sjöling
mesh_terms: D000483:Alleles; D001427:Bacterial Toxins / Q000737:chemistry / Q000235:genetics*; D004768:Enterotoxins / Q000737:chemistry / Q000235:genetics*; D004927:Escherichia coli Infections / Q000235:genetics*; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics*
chemical_list: D001427:Bacterial Toxins; D004768:Enterotoxins; D029968:Escherichia coli Proteins; C027538:heat-labile enterotoxin, E coli