Phylogenetic typing
The E. coli isolates were phylogenetically classified into eight phylo-groups: based on four genetic markers, namely arpA, yjaA, chuA, and TspE4.C2. The phylogenetic grouping of the E. coli isolates was carried out by using a quadruplex PCR reaction (Clermont et al., 2013). All the primer sequences and PCR conditions are given in Table S1.