Purpose: To examine the impact of low temperature (4° C) on stress and virulence gene expression in non-O157 STEC.
Methods: Logarithmic phase cultures of E. coli O26, O103, O104, O111, O145 and O157 were exposed to 4°C for 7 d. Expression of virulence (stx1A, stx2A and eae), cold stress (cspA, cspC and cspE) and stress response (rpoS and uspA) genes was examined using a two-step reverse-transcription comparative quantitative real-time PCR. Data was analyzed using Biogazelle’s qbasePLUS (ANOVA, significance P < 0.05, cut-off at 2-fold difference in gene expression).
Results: CspA (cold-shock protein A) was upregulated (P < 0.05) in all serotypes, while cspC and cspE were not differentially expressed. Expression of cspA was 5 to 25 fold higher in E. coli O157:H7 than all other serotypes. Cold stress slightly increased (<3.5 fold) the expression of eae (attaching and effacing) in all serotypes in which the gene was present, but expression of stx1A (Shiga toxin) was unaffected (P > 0.05). Stx2A showed slight upregulation in E. coli O104:H4, but the difference in expression fell below the 2-fold cut off. Variable gene expression was observed for both of the stress response genes, with rpoS showing slight upregulation compared to uspA, but neither were differentially expressed from the control.
Significance: The results of the study provide a basic understanding of cold temperature acclimatization of non-O157 STEC, thereby providing knowledge which can be used to develop effective mitigation strategies for their control.