Molecular and Phenotypic Characterization ofEscherichia coliAssociated with Granulomatous Colitis of Boxer Dogs

InvasiveEscherichia coliis causally associated with granulomatous colitis (GC) of Boxer dogs and French Bulldogs. The virulence determinants of GCE. coliare unclear.E. coliisolated from 16 GC (36 strains) and 17 healthy control (HC: 33 strains) dogs were diverse in phylogeny, genotype, and serotype and lacked diarrheagenic genes. Genes encoding type II (gsp), IV (traC), and VI (hcp) secretion systems, long polar fimbriae (lpfA154/141), and iron acquisition (fyuA,chuA) were frequent in GC and HC.E. colifrom 14/15 GC and 10/11 HC invaded Caco-2 better than non-pathogenicE. colistrain DH5 alpha, with invasion correlated with motility and presence ofchuAandcolV.E. colifrom all GC and 10/11 HC survived better than DH5 alpha in J774 macrophages, with adherent-invasiveE. coli(AIEC) in 60% GC and 73% HC. AIEC replicated in monocyte derived macrophages from a GC Boxer with CD48/SLAM risk haplotype but not the HC. Fluroquinolone resistantE. coliwere less motile and invasive than fluoroquinolone sensitive (p< 0.05), and only 1/8 resistant strains met criteria for AIEC. In conclusion GCE. coliare diverse, resemble extraintestinal pathogenicE. coli(ExPEC), including AIEC, and can replicate in GC-susceptible macrophages. They are likely resident pathosymbionts that can opportunistically persist within macrophages of a GC-susceptible dog.