The neighbor-joining cluster analysis was employed to assign new subtypes or variants as mentioned by Scheutz et al. [62]. Identification of virulence and adherence factors All STEC isolates were tested by PCR to investigate the presence of astA, hemolysis related genes (ehxA and hlyA), HPI genes (fyuA and irp) and adhesion-related genes (eae, paa, efa1, toxB, lpfA O157/OI-154, lpfA O157/OI-141, lpfA O113, saa, F4, F5, F6, F17, F18 and F41) using the primers listed in Table 3. Antimicrobial susceptibility testing Antimicrobial resistance was determined by the disc diffusion method
[75]. Twelve antimicrobial groups covering 23 antimicrobial agents including penicillins (ampicillin and piperacillin), β-lactam/β-lactamase inhibitor combinations (amoxicillin-clavulanic acid and ampicillin-sulbactam),
Necrostatin-1 nmr cephems (parenteral) (cephalosporins I, II, III, and IV, cefepime, cefotaxime, ceftriaxone, cephalothin VX-680 in vivo and cefuroxime), monobactams (aztreonam), carbapenems (imipenem and meropenem), aminoglycosides (gentamicin, kanamycin and streptomycin), tetracyclines (tetracycline), fluoroquinolones (ciprofloxacin, norfloxacin and levofloxacin), quinolones (nalidixic acid), folate pathway inhibitors (trimethoprim-sulfamethoxazole), phenicols (chloramphenicol) and nitrofurans (nitrofurantoinz) were tested. Results were interpreted using the Clinical and Laboratory Standards Institute (CLSI, 2012) breakpoints, when available. E. coli ATCCR 25922 was used as quality
control. PFGE and MLST STEC isolates were digested Florfenicol with XbaI and separated by PFGE using the non-O157 STEC PulseNet protocol (http://www.pulsenetinternational.org). Gel images were converted to Tiff files and then analyzed using BioNumerics software (Applied Maths, Sint-Martens-Latem, Belgium). MLST was performed according to the recommendations of the E. coli MLST website (http://mlst.ucc.ie/mlst/dbs/Ecoli) using 7 housekeeping genes (adk, fumC, gyrB, icd, mdh, purA and recA). Alleles and sequence types (STs) were determined following the website instructions [76]. MLST data for the HUS-associated MRT67307 enterohemorrhagic E. coli (HUSEC) collection were obtained from http://www.ehec.org[52]. All human STEC STs from the E. coli MLST databases were downloaded for comparison. A minimum spanning tree based on these STs was generated with BioNumerics software. Four novel alleles, fumC470, gyrB351, icd396 and recA267 were submitted to E. coli MLST website. The sequences obtained in this study have been deposited in GenBank: KC924398 (icd396), KC924399 (gyrB351), KC924400 (fumC470), KC924401 (recA267) and KC339670 (a new variant of stx 2e). Statistical analysis Statistical tests were performed using SAS, Version 9.1 (SAS Institute Inc., Cary, NC., USA). Statistically significant differences were calculated using a χ2 test where appropriate. P values of <0.05 were considered statistically significant.