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).