Distribution and molecular analysis of Subtilase cytotoxin gene (subAB)
variants in Shiga toxin-producing Escherichia coli (STEC) isolated from
different sources in Iran
Abstract
Subtilase is a potent cytotoxin 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. In the present study a collection of 101 STECs
isolated from various sources in Iran (2009-2016) were analyzed for the
detection of different genes encoding the subtilase variants, plasmidic
and chromosomal virulence genes, together with the phylogroup 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). 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. Concerning the virulence markers, some strains showed an
association with hosts the bacteria were isolated from. In particular,
tia was associated with sheep, goats and pony isolates and astA gene was
present in deer, pony and goats and terD was only found in deer and pony
isolates. Only cattle STEC carried espP and epeA, the important markers
of pO113 plasmid. Some genes were widespread among strain of various
sources like ehly, iha and lpfO113 and some genes were not detected such
as efa1, toxB and katP. Most strains belonged to phylogenetic group B1
(89.47%), but five strains from cattle, deer, pony and a goat were
assigned to A phylogroup. Most cattle strains belonged to O113, while O5
was just detected in ovine isolates, and O128 and O113 were present in
caprine strains. In conclusion, the present study reveals the presence
of potentially pathogenic genotypes among LEE-negative isolates and some
host specificity related to subtilase variants and other virulence
markers that may aid in source tracking of STEC during outbreaks.