Molecular and in silico analyses for detection of Shiga toxin-producing Escherichia coli (STEC) and highly pathogenic enterohemorrhagic Escherichia coli (EHEC) using genetic markers located on plasmid, O Island 57 and O Island 71

Due to the diversity of Shiga toxin-producing Escherichia coli (STEC) isolates, detecting highly pathogenic strains in foodstuffs is challenging. Currently, reference protocols for STEC rely on the molecular detection of eae and the stx1 and/or stx2 genes, followed by the detection of serogroup-specific wzx or wzy genes related to the top 7 serogroups. However, these screening methods do not distinguish between samples in which a STEC possessing both determinants are present and those containing two or more organisms, each containing one of these genes. This study aimed to evaluate ecf1, Z2098, Z2099, and nleA genes as single markers and their combinations (ecf1/Z2098, ecf1/Z2099, ecf1/nleA, Z2098/Z2099, Z2098/nleA, and Z2099/nleA) as genetic markers to detect potentially pathogenic STEC by the polymerase chain reaction (PCR) in 96 animal samples, as well as in 52 whole genome sequences of human samples via in silico PCR analyses. In animal isolates, Z2098 and Z2098/Z2099 showed a strong association with the detected top 7 isolates, with 100% and 69.2% of them testing positive, respectively. In human isolates, Z2099 was detected in 95% of the top 7 HUS isolates, while Z2098/Z2099 and ecf1/Z2099 were detected in 87.5% of the top 7 HUS isolates. Overall, using a single gene marker, Z2098, Z2099, and ecf1 are sensitive targets for screening the top 7 STEC isolates, and the combination of Z2098/Z2099 offers a more targeted initial screening method to detect the top 7 STEC isolates. Detecting non-top 7 STEC in both animal and human samples proved challenging due to inconsistent characteristics associated with the genetic markers studied.