Phylogenetic relationships of the STEC isolates with human HUS-causing E. coli (HUSEC)
A minimum spanning tree was constructed based on MLST STs of our isolates and HUSEC isolates to evaluate the potential risk in causing human infection (Figs. 2 and S1). The results suggested that some isolates are related to certain strains from HUSEC collection. ST675 contains four sheep isolates and HUSEC039, all belonging to serotype O76:H19. They all contain stx 1c only and ehxA . ST25 includes a sheep strain SG18-6-2 and HUSEC028, both typed into O128:H2. These contain both ehxA and iha , and carrystx 1c+stx 2b. ST40 contains four sheep isolates (stx 1c, eae -, ehxA -, and saa -) and HUSEC023 (stx 2d, eae -, ehxA -, and saa -), belonging to O108 and O112, respectively. ST101 contains two cattle isolates (O81,stx 1a+stx 2a, eae -, saa +, and iha +) and HUSEC025 (O55, stx 1, eae -, saa +, andiha +). ST43 contains three strains, one cattle isolate CD15-213, one sheep isolate SG17-J10, and HUSEC001. These are very different in terms of O serogroup and virulence gene contents. Isolate CD15-213 tested positive for all nine virulence genes, implying high virulence potential (Fig. 1).