Distribution and molecular analysis of Subtilase cytotoxin gene (subAB) variants in Shiga toxin-producing Escherichia coli (STEC) isolated from different sources in Iran.

Subtilase exhibits strong cytotoxicity that was first described in O113:H21 strain in Australia as a plasmid- encoded cytotoxin (subAB1). Subsequently, chromosomal variants including subAB2-1, subAB2-2, and subAB2-3 were described. We aimed to investigate the presence of subAB genes in a collection of Shiga toxin-producing Escherichia coli (STEC) strains (n=101) isolated from different sources in Iran. A collection of 101 archived STEC strains isolated from cattle (n=50), goats (n=25), sheep (n=15), wild captive animals (n=8: persian fallow deer, n=3; caspian pony, n=1; Macaca mulatta, n=4), and humans (n=3) during 2007-2016 were analyzed for the detection of different genes encoding the Subtilase variants, plasmidic and chromosomal virulence genes, phylogroups and serogroups. Overall, 57 isolates (56.4%) carried at least one variant of subAB. Most strains from small ruminants including 93% of sheep and 96% of caprine isolates carried at least one chromosomally encoded variant (subAB-2-1 and/or subAb2-2). In contrast, 12 cattle isolates (24%) only harbored the plasmid encoded variant (subAB1). STEC strains from other sources, including deer, pony and humans were positive for subAB-2-1 and/or subAb2-2. Our results reveal the presence of potentially pathogenic genotypes among locus of enterocyte effacement (LEE)-negative isolates, and some host specificity related to Subtilase variants and other virulence markers that may aid in source tracking of STEC during outbreak investigations.