Abstract:

An enterohemorrhagic Escherichia coli (EHEC) O157: H7 strain EC169 carrying both stx1 and stx2 genes but
not producing Shiga toxins was used in this study to investigate the reason for these characteristics. The stx1 gene and its
upstream region from EC169 were amplified by hiTAIL-PCR. Sequencing data showed that EC169 q gene had 6 single
nucleotide polymorphism (SNP) sites compared with the corresponding region of the typical strain sakai. A highly virulent
O157:H7 strain EC150 and a hypovirulent O157: H7 strain EC157 were tested in this study. The full length of EC150 q
gene was amplified and connected to the expression vector pkk223. The recombinant plasmid was then transformed into
EC169 and EC157, respectively. The qRT-PCR results showed that the pkk223-q vector was efficiently expressed in the
two recombinant strains, respectively. qRT-PCR and RPLA results demonstrated that the level of Shiga-toxin expression
was improved in EC157 recombinant strain, but its expression was not changed in EC169 recombinant strain. These results
suggest that the SNP variation of protein Q might not be responsible for the non-expression of Shiga-toxins in EC169,
suggesting that other mechanisms may be involved in controlling the expression of Shiga-toxins in EC169. This study might
contribute to study the control and regulation of Stx phage.

Key words: E. coli O157: H7, protein Q, qRT-PCR, Shiga-toxin, hiTAIL-PCR