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Enterohaemorrhagic Escherichia coli (EHEC) O157:H7 mounts specific acid-resistance systems against acid stress, making it more difficult to eradicate in food industry. To date, RNAseq-based analysis focusing on the virulence factors within an acidic environment is restricted to asmall part of virulence gene clusters. In this study E.coli O157:H7 survived HCl stress at pH 3.0 for up to 1 h preceded by acid adaptation at pH 5.5 for 1 h. At the same time, bacteria without stimulus were cultured in neutral TSB broth for 2 h.Then, transcriptome analysis was performed to compare virulence-related genes at neutral and acidic pH. Though transcripts indicated adownshift of the flagellar, fimbriae and LEE-associated genes, the increased expression of adhesin-related genes, iron uptake genes and some potential virulence factors were identified. Comparison of the gene expression with respect to virulence factors revealed strongest cell response to the relevant stress and increased protective response for survival in the acidic pH. This suggests that E.coli O157:H7 might be still virulent following HCl stress. [ABSTRACT FROM AUTHOR]