Safety assessment of the biocontrol of Shiga toxin-producing Escherichia coli using bacteriophages

Abstract

Shiga-toxin producing Escherichia coli (STEC) is an important foodborne pathogen. Although strictly lytic phages have been considered promising tools for STEC biocontrol, safety issues related to Shiga toxin production and emergence of bacteriophage insensitive mutants (BIMs) need to be investigated. We report the isolation of two lytic phages, vB_EcoS_Ace (Ace) and vB_EcoM_Shy (Shy) and the characterization of their infective parameters, genome content and biostability. We show that Ace was more efficient in controlling STEC planktonic cells and did not stimulate the production of the Stx prophage nor Shiga toxin. BIMs were only detected after a reintroduction of Ace to a previously infected culture. Resistance gain was associated with lower virulence, as some BIMs did not agglutinate with O157-specific antibody and were more vulnerable to human serum complement. There were no differences between the wild-type strain and the BIMs biofilm formation capacity and susceptibility to disinfectants. Overall, this work demonstrated that phage Ace, can be use as a safe biocontrol agent against STEC contamination and that the burden of BIM emergence is not associated to a greater risk for environmental persistence and human pathogenicity.