Thirty-nine Shiga toxin-producing Escherichia coli (STEC) O113 Irish farm, abattoir, and clinical isolates were analyzed in conjunction with eight Australian, New Zealand, and Norwegian strains for H (flagellar) antigens, virulence gene profile (eaeA, hlyA, tir, espA, espB katP, espP, etpD, saa, sab, toxB, iha, lpfAO157 OI-141, lpfAO113, and lpfA O157 OI-154), Shiga toxin gene variants (stx1c, stx 1d, stx2, stx2c, stx2dact, stx 2e, stx2f, and stx2g) and were genotyped using pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). All of the Irish strains were O113 H4, regardless of source, while all non-Irish isolates carried the H21 flagellar antigen. The stx1 gene was present in 30 O113 H4 strains only, whereas the stx2d gene was common to all isolates regardless of source. In contrast, eaeA was absent, while hlyA was found in the Australian, New Zealand, Norwegian, and two of the Irish human clinical isolates. saa was present in the O113 H21 but not in the O113 H4 serotype. To the best of the author s knowledge, this is the first report of clinically significant STEC lacking both the eaeA and saa genes. PFGE analysis was inconclusive; however, MLST grouped the strains into three sequence types (ST) ST10, ST56, and ST223. Based on our findings, it was concluded that the stx2d gene is common in STEC O113, which are generally eaeA negative. Furthermore, STEC O113 H4 is a new, emerging bovine serotype of human clinical significance. Copyright 2012, Mary Ann Liebert, Inc. 2012.