Construction of a stx2 deletion mutant of Shiga toxin 2 phage FMin27and its infectious properties

Abstract:

[Objective] To construct an stx2 gene mutant phage FMin27(Δstx∷cat) and to observe its infectiousness of various serotypes Escherichia coli strains. [Methods] With the help of Red recombinant system, the stx2 gene of the E. coli O157:H7 Min27 strain isolated from intestinal feces of piglet with diarrhea at a swine farm of Shanghai, was replaced by the chloramphenicol acetyltrasferase (cat) gene from plasmid pLacI. Phage FMin27(Δstx∷cat) was isolated after in-duction of E. coli Min27(Δstx∷cat) strain with mitomycin C. Twenty-one E. coli strains with various serotypes were infected with FMin27(Δstx∷cat), and plaque formation and lysogenic conversion of them were investigated. [Results] Of the 21 E. coli isolates, 2 with the serotypes of O60 and O138 integrated the FMin27(Δstx∷cat) in their chromosomes and expressed resistance to chloramphenicol. With the exception of one laboratory E. coli strain MG1655, none of the tested E. coli strains supported the formation of plaques and lysogenization when used as indicators for FMin27(Δstx∷cat). Fol-lowing induction with mitomycin C, these lysogenic strains released infectious particles of FMin27(Δstx∷cat) that formed plaques on a lawn of E.coli laboratory strain MC1061. [Conclusion] These results demonstrated that FMin27(Δstx∷cat) was able to infect and lysogenize particular E. coli strains and that the lysogens could produce infec-tious phage progeny. It could be inferred that Stx bacteriophages were able to spread exogenous genes among E. coli strains. The work provided a basis for further study on mechanisms of Stx phages infection and control of Stx expression.