THE PREVALENCE OF Stx1, Stx2 GENES AND THEIR SEQUENCING VARIATION IN E. coli O157:H7 STRAIN ISOLATED FROM DIFFERENT SOURCES

Abstract

Background: The two type of Shiga toxin (Stx1, Stx2) is the most important virulence factors associated with the pathogenicity of E. coli O157:H7. Aim: The current study aimed to detect these toxins and study their sequence alignment in E. coli O157:H7 isolated from different sources. Materials and Methods: Stx1 and Stx2 genes were detected by conventional PCR technique using specific primers. Sequencing of genes was performed by using Sanger sequencing methods. Results: The results indicate that the presence of the Stx1 gene is low in all the isolates compared to the gene Stx2 which was the most present in the studied isolates. Diarrheal isolates were the most isolates that carry Stx1 and Stx2 genes, and the least are the environmental isolates. Gene sequential analysis results showed that both genes, Stx1, and Stx2, belong to the E.coliO157:H7 strain with a match rate of 99% compared to the NCBI database, ten new strains of E.coliO157:H7 were registered in the NCBI database and each of them was given its serial number. The genetic changes that were detected in new strains varied between transversion and transition, which led to the occurrence of different types of point mutations, including missense and silent mutations. Conclusion: The presence and spread of Stx1 and Stx2 genes vary depending on the source of E.coliO157:H7 strain isolation and the genetic sequence of these genes can change as a result of different mutations.