Hemorrhagic pneumonia (HP) is a rare but highly lethal disease, mainly of dogs and cats, caused by hemolytic
Escherichia coli
strains that contain
cnf1
(encoding cytotoxic necrotizing factor 1). After encountering fatal HP in two dogs, we used contemporary molecular methods, including multi-locus sequence typing and whole genome sequencing, to compare the corresponding case isolates with published HP clinical isolates and newly-obtained fecal
E. coli
isolates from 20 humans and animals in the index HP case household. We also compared the aggregated HP clinical isolates, which represented 13 discrete strains, by pulsotype with a large, private pulsotype library of diverse-source
E. coli
. The HP clinical isolates represented a narrow range of phylogenetic group B2 lineages (mainly sequence types 12 and 127), O types (mainly O4 and O6), and H types (mainly H5 and H31), but diverse
fimH
alleles (type-1 fimbriae adhesin). Their extensive, highly conserved virulence genotypes, which qualified as extraintestinal pathogenic
E. coli
(ExPEC), encoded diverse adhesins, toxins, iron uptake systems, and protectins. Household surveillance identified multiple HP-like fecal strains, plus abundant between-host strain sharing, including of the household's index HP strain. The pulsotype library search identified, for five HP clinical strains, same-pulsotype human and animal fecal and clinical (predominantly urine) isolates, from diverse locales and time periods. Thus,
E. coli
strains that cause HP derive from a narrow range of ExPEC lineages within phylogroup B2, contain multiple virulence genes other than
cnf1
, are shared extensively between hosts, and likely function in nature mainly as intestinal colonizers and uropathogens.
Importance
This study clarifies the clonal background and extensive virulence genotypes of the
E. coli
strains that cause hemorrhagic pneumonia in domestic animals (mainly dogs and cats), shows that such strains circulate among animals and humans, identifies a substantial intestinal colonization component to their lifestyle, and extends their known clinical manifestations to include bacteremia and urinary tract infection. The findings place these strains better into context vis-a-vis current understandings of
E. coli
phylogeny, ecology, and pathogenesis; identify questions for future research; and may prove relevant for surveillance and prevention efforts.