Clonality and virulence traits of Escherichia coli associated with hemorrhagic septicaemia in turkeys

Fifty-five clinical isolates of avian pathogenic Escherichia coli (APEC) from seven outbreaks of acute hemorrhagic septicaemia in turkeys were characterised by serotyping, plasmid profiling including restriction analysis with HindIII, ribotyping with EcoRI and HindIII, multilocus sequence typing (MLST) and virulence profiling. A clonal relationship was demonstrated for each outbreak according to serotype, plasmid profiling, ribotyping, and MLST.In addition, isolates demonstrated highly similar virulence profiles, as all isolates were positive for F11 pili and possessed genes encoding aerobactin (iucD), increased serum survival (iss), temperature-sensitive hemagglutatin (tsh) and colicin V plasmid operon genes (cva/cvi). However, only 20% of the isolates produced colicin V and 42% exhibited serum resistance. All strains with O group O111 and a single O18ac strain (demonstrating non-clonal DNA profiles) were positive for enteroaggregative heat stabile toxin (EAST1), while isolates of a single outbreak all possessed the enteroaggreative toxin gene (astA). All isolates were negative for genes encoding verocytotoxins (vtx/stx), iron-repressible protein (irp2), P-fimbria (papC), invasion plasmid antigen (ipaH), attaching and effacing gene (eae), enterohaemolysin (ehxA), and enterotoxins LT, STIa (STp) and STIb (STh). In conclusion, highly similar virulence profile were demonstrated for isolates of E. coli associated with a single well-defined lesion type of colibacillosis in turkeys; acute hemorrhagic septicaemia. Isolates obtained, however, demonstrated a different phylogenetic background, underlining the importance of using well-defined strain collections for characterization of APEC pathotypes.