Regulatory elements of stx2 gene and the expression level of shiga like-toxin 2 producing Escherichia coli O157 H7

Abstract Background/Purpose: Shiga like-toxin is an important factor in the pathogenesis of Escherichia coli O157:H7 infection and responsible for some of severe complications. The Shiga like-toxin 2 is usually associated with the hemolytic uremic syndrome in human. Its expression is regulated by the regulatory elements locating at the upstream of stx2 gene including stx2-promoter sequence, ribosome binding site, and the antiterminator q gene. The present study aimed to find out the correlation between regulatory elements and the expression level of Stx2 in two locally isolates of E. coli O157:H7. Methods: Two locally E. coli O157:H7 strains SM-25(1) and KL-48(2) originated from human and cattle feces, respectively, and an E. coli reference strain ATCC 43894 were investigated. The complete stx2 gene covering the sequences of promoter, ribosome binding site, and open reading frame and q gene of each strain was analyzed. The magnitude of Stx2 production was detected with a reverse passive latex agglutination method and Stx mediated cellular damage was determined by using Vero cell assay. Results: A comparison of the complete stx2 gene contained stx2-promoter, ribosome binding site and q genes of two locally strains KL-48(2) and SM25(1), and the E. coli ATCC 43894 showed that the amino acid sequences identically. The both locally isolates occurred the Stx negative in a reverse passive latex agglutination and non-toxic in Vero cell assay. Conclusion: The expression level of Shiga-like toxin of the two locally isolates E. coli O157:H7 was not only depending on regulatory elements of stx2 gene. Keywords: E. coli O157:H7, promoter, q gene, ribosome binding site, Stx2 titer