Characteristics of Bacteriophage Isolates and Expression of Shiga Toxin Genes Transferred to Non Shiga Toxin-Producing E. coli by Transduction

A risk analysis of Shiga toxin (Stx)-encoding bacteriophage was carried out by confirming the transduction phage to non-Stx-producing Escherichia coli (STEC) and subsequent expression of the Shiga toxin genes. The virulence factor stx1 was identified in five phages, and both stx1 and stx2 were found in four phages from a total of 19 phage isolates with seven non-O157 STEC strains. The four phages, designated as phi NOEC41, phi NOEC46, phi NOEC47, and phi NOEC49, belonged morphologically to the Myoviridae family. The stabilities of these phages to temperature, pH, ethanol, and NaClO were high with some variabilities among the phages. The infection of five non-STEC strains by nine Stx-encoding phages occurred at a rate of approximately 40%. Non-STEC strains were transduced by Stx-encoding phage to become lysogenic strains, and seven convertant strains had stx1 and/or stx2 genes. Only the stx1 gene was transferred to the receptor strains without any deletion. Gene expression of a convertant having both stx1 and stx2 genes was confirmed to be up to 32 times higher for Stx1 in 6% NaCl osmotic media and twice for Stx2 in 4% NaCl media, compared with expression in low-salt environments. Therefore, a new risk might arise from the transfer of pathogenic genes from Stx-encoding phages to otherwise harmless hosts. Without adequate sterilization of food exposed to various environments, there is a possibility that the toxicity of the phages might increase. Shiga toxins (Stx) are a group of bacterial toxins those cause human and animal diseases. Stx is produced primarily by Escherichia coli and Shigella dysenteriae, and sporadically by Citrobacter freundii, Enterobacter cloacae, and S. flexneri [1]. Stx has two major types: Shiga toxin1 (Stx1) and Shiga toxin2 (Stx2). Stx1 and Stx2 have very similar biochemical properties and mechanisms, however, their immunological characteristics are different. Clinically, Stx2 is approximately 1000 times more toxic than Stx1 [2, 3].

Automated summary

This study conducted a risk analysis on Stx-encoding bacteriophages by confirming their ability to transduce non-Stx-producing Escherichia coli and express the Shiga toxin genes. The results showed that non-STEC strains could be transduced by Stx-encoding phages, leading to an increased risk of harmful gene transfer. Additionally, the study found that the stability of these phages to various environmental factors was high, highlighting the potential risks associated with inadequate sterilization practices.