Escherichia coli is a common commensal of vertebrates with a genome size of about 4500 genes. Half are common to all strains of the species with the balance drawn from a gene pool of more than 15,000 genes. Considerable substructure in E. coli occurs so that, at the subspecies level, E coli consists of multiple phylogroups. These have been designated as A, B1, B2 and D (the major groups) and C, E, F and Clade 1 (the minor groups). Subspecies or strains of the different phylogroups differ in their genome size, gene content, ecological niche, life history traits and propensity to cause disease.
Although most E.coli behave as commensals, some strains cause septicaemia and urinary tract infections in humans and companion animals. These are usually representatives of phylogroups B2 and D.
Of the probably thousands of B2 and D strains, in humans the great majority of strains belong to one of a dozen lineages, known as sequence types (STs). In phylogroup B2 these are STs 131, 73, 95 and 127 and ST 69 in phylogroup D. These STs cause most E. coli urinary tract and septicaemic infections.
STs 73, 95,127 and 131 account for about 50% of all B2 strains seen in humans. ST 69 accounts for around 20% of all D strains.
I aim to explore the likelihood E.coli in companion animals pose a source of these human associated strains. To date, I have assigned E coli faecal isolates from over 160 dogs and 200 cats in Canberra to phylogroups and STs. 21% and 43% of isolates from dogs and cats, respectively were phylogroup B2 and 6% of dog isolates and 8% of cat isolates are phylogroup D. Of these, 64% and 44% of B2 isolates and 29% and 11% of D isolates in cats and dogs, respectively, were human associated STs. Whole genome sequencing of representative isolates will allow a more detailed characterisation of these human associated isolates.