Purpose: The objective of this study was to establish a relationship between the exposure of O157 and non-O157 STEC to environmental stresses and the expression of virulence-associated genes.
Methods: Four O157:H7 and six non-O157 STEC (O26:H11, O103:H1, O104:H4, O111:NM, O121:NM, and O145:NM strains) strains were repeatedly exposed to sub-lethal chlorine (2 ppm), osmotic (aw 0.97), or acid (pH 5) stress, followed by quantification of the virulence-associated stx1, stx2, and eae genes using quantitative real-time RT-PCR assay.
Results: When the stressed strains were compared with non-stressed control strains, only chlorine-stressed O103:H1, O104:H4, O145:NM, and O157:H7 showed a significant (P<0.05) increase (>1.4 fold) in relative gene expression of stx1. A significant increase in relative gene expression of stx2 was observed for chlorine-stressed O103:H1 (>2.0 fold) or O26:H11 (1.92 fold) cells, while a slight increase (1.27 to 1.38 fold) in gene expression was observed for O104:H4 and O145:NM cells. Chlorine-stressed cells of O111:NM, O121:NM, and O157:H7 showed similar or a slightly less expression of the selected genes than the control. The relative gene expression levels of eae were similar to the patterns of stx1 and stx2, except for stressed cells of O111:NM with a 2.0-fold increase in eae gene expression.
Significance: Result showed that STEC had increased expression levels of virulence genes after surviving chlorine stress, suggesting that the increased expression may lead to higher virulence of STEC.