Molecular serotyping of Shiga toxin-producing Escherichia coli (STEC) of animal origin in Iran reveals the presence of important non-O157 seropathotypes

The present study reported the first serotyping (O:H typing) data documented in Shiga toxin-producing Escherichia coli (STEC) strains of animal origin in Iran in isolates recovered between 2008 to 2016. A total number of 75 STEC strains previously isolated from fecal samples of cattle, sheep, goats, pigeons, humans, and deer were assessed by different polymerase chain reaction (PCR) assays detecting the major virulence genes of STEC and phylogroups. Then, the strains were tested for the 16 important O-groups by PCR. Finally, twenty strains were selected for H-genotyping by PCR plus sequencing. The predominant serogroup was O113 which was detected in nine isolates (five cattle, 55.50%; two goats, 22.20%; two red deer, 22.20%) followed by O26 (3/3, 100%) in cattle, O111 (3/3, 100%) in cattle, O5 (3/3, 100%) in sheep, O63 (1/1, 100%) in pigeon, O75 (2/2, 100%) in pigeons, and O128 in goats (2/3, 66.60%) and pigeon (1/3, 33.30%). The most important recognized serotypes were O113:H21 in cattle (2/3) and goat (1/3), O113:H4 in red deer (1/1), O111:H8 in calves (2/2), O26:H11 in calve (1/1), O128:H2 in goats (2/3) and pigeon (1/3), and O5:H19 in sheep (3/3). One cattle strain carrying stx1, stx2, eae, and Ehly genes belonged to O26:H29 serotype. Most strains with determined O-groups were from the bovine source that highlighted the importance of cattle as reservoirs of potentially pathogenic serovars. The present study suggested that the top seven non-O157 serogroups should be assessed along with O157 in all future research and clinical diagnostics of STEC in Iran.