title: Evidence for Contemporary Switching of the O-Antigen Gene Cluster between Shiga Toxin-ProducingEscherichia coliStrains Colonizing Cattle.
abstract: Shiga toxin-producingEscherichia coli(STEC) comprise a group of zoonotic enteric pathogens with ruminants, especially cattle, as the main reservoir. O-antigens are instrumental for host colonization and bacterial niche adaptation. They are highly immunogenic and, therefore, targeted by the adaptive immune system. The O-antigen is one of the most diverse bacterial cell constituents and variation not only exists between different bacterial species, but also between individual isolates/strains within a single species. We recently identified STEC persistently infecting cattle and belonging to the different serotypes O156:H25 (n= 21) and O182:H25 (n= 15) that were of the MLST sequence types ST300 or ST688. These STs differ by a single nucleotide inpurAonly. Fitness-, virulence-associated genome regions, and CRISPR/CAS (clustered regularly interspaced short palindromic repeats/CRISPR associated sequence) arrays of these STEC O156:H25 and O182:H25 isolates were highly similar, and identical genomic integration sites for thestxconverting bacteriophages and the core LEE, identical Shiga toxin converting bacteriophage genes forstx1a, identical complete LEE loci, and identical sets of chemotaxis and flagellar genes were identified. In contrast to this genomic similarity, the nucleotide sequences of the O-antigen gene cluster (O-AGC) regions betweengalFandgndand very few flanking genes differed fundamentally and were specific for the respective serotype. Sporadic aEPEC O156:H8 isolates (n= 5) were isolated in temporal and spatial proximity. While the O-AGC and the corresponding 5' and 3' flanking regions of these aEPEC isolates were identical to the respective region in the STEC O156:H25 isolates, the core genome, the virulence associated genome regions and the CRISPR/CAS elements differed profoundly. Our cumulative epidemiological and molecular data suggests a recent switch of the O-AGC between isolates with O156:H8 strains having served as DNA donors. Such O-antigen switches can affect the evaluation of a strain's pathogenic and virulence potential, suggesting that NGS methods might lead to a more reliable risk assessment.
authors.affiliation: Friedrich-Loeffler-Institut/Federal Research Institute for Animal Health, Institute of Molecular Pathogenesis Jena, Germany.
authors.forename: Lutz
authors.initials: L
authors.lastname: Geue
authors.affiliation: Friedrich-Loeffler-Institut/Federal Research Institute for Animal Health, Institute of Molecular Pathogenesis Jena, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Menge
authors.affiliation: Institute of Microbiology and Epizootics, Free University Berlin Berlin, Germany.
authors.forename: Inga
authors.initials: I
authors.lastname: Eichhorn
authors.affiliation: Institute of Microbiology and Epizootics, Free University BerlinBerlin, Germany; Robert Koch InstituteBerlin, Germany.
authors.forename: Torsten
authors.initials: T
authors.lastname: Semmler
authors.affiliation: Institute of Microbiology and Epizootics, Free University BerlinBerlin, Germany; Robert Koch InstituteBerlin, Germany.
authors.forename: Lothar H
authors.initials: LH
authors.lastname: Wieler
authors.affiliation: Wellcome Trust Sanger Institute, Pathogen Genomics Cambridge, UK.
authors.forename: Derek
authors.initials: D
authors.lastname: Pickard
authors.affiliation: Friedrich-Loeffler-Institut/Federal Research Institute for Animal Health, Institute of Molecular Pathogenesis Jena, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Berens
authors.affiliation: Friedrich-Loeffler-Institut/Federal Research Institute for Animal Health, Institute of Molecular Pathogenesis Jena, Germany.
authors.forename: Stefanie A
authors.initials: SA
authors.lastname: Barth
keywords: E. coli; O-antigen gene cluster; STEC; genome sequencing; recombination