The interactions of bacteriophage Ace and Shiga toxin-producingEscherichia coliduring biocontrol

Abstract

Strictly lytic phages are considered powerful tools for biocontrol of foodborne pathogens. Safety issues needed to be addressed for the biocontrol of Shiga toxin-producing Escherichia coli (STEC) include: lysogenic conversion, Shiga toxin production through phage induction, and emergence/proliferation of bacteriophage insensitive mutants (BIMs). To address these issues, two new lytic phages, vB_EcoS_Ace (Ace) and vB_EcoM_Shy (Shy), were isolated and characterized for life cycle, genome sequence and annotation, pH stability, and efficacy at controlling STEC growth. Ace was efficient in controlling host planktonic cells and did not stimulate the production of the Stx prophage or Shiga toxin. A single dose of phage did not lead to the selection of BIMs. However, when reintroduced, BIMs were detected after 24h of incubation. The gain of resistance was associated with lower virulence, as a subset of BIMs failed to agglutinate with O157-specific antibody and were more sensitive to human serum complement. BIM's biofilm formation capacity and susceptibility to disinfectants was equal to that of the wild-type strain. Overall, this work demonstrated that phage Ace is a safe biocontrol agent against STEC contamination and that the burden of BIM emergence did not represent a greater risk in environmental persistence and human pathogenicity.

Microbial Antagonism in Food-Enrichment Culture: Inhibition of Shiga Toxin-Producing Escherichia coli and Shigella Species

“…Bacteriophages active against STEC have been isolated from numerous zoonotic sources and may be relatively common indicating potential importance for enrichment cultures ( Litt et al, 2018 ; Mangieri et al, 2020 ; Pinto et al, 2021 ). Presence of bacteriophages active against target species in enrichment cultures has been shown to reduce relative proportions of target Salmonella and S. sonnei by over a log indicating their critical impact on food microbiological methods ( Muniesa et al, 2005 ).…”

An in vitro fermentation model to study the impact of bacteriophages targeting Shiga toxin-encoding Escherichia coli on the colonic microbiota

“…Some antibiotics are known to induce Shiga phages, which can increase the risk of developing haemolytic-uremic syndrome (HUS) disease 10 . On the other hand, lytic phages were already shown to be able to control the growth of STEC strains without inducing this response 7 , 12 .…”

“…In this study, we propose an in vitro model that uses faecal slurry from healthy donors to characterize the impact of phage preparation on the colonic microbiota. We used a previously isolated and characterized phage, named phage vB_EcoS_Ace (Ace) 12 , which is highly specific towards serotype O157:H7, the most known STEC serotype. Furthermore, this phage was shown to be able to infect other closely related species, strains of Citrobacter freundii and Shigella sonnei 12 .…”

“…We used a previously isolated and characterized phage, named phage vB_EcoS_Ace (Ace) 12 , which is highly specific towards serotype O157:H7, the most known STEC serotype. Furthermore, this phage was shown to be able to infect other closely related species, strains of Citrobacter freundii and Shigella sonnei 12 . Phage Ace belongs to the Demerecviridae family, more specifically to the Tequintavirus genus.…”

“…Phage Ace belongs to the Demerecviridae family, more specifically to the Tequintavirus genus. Even though phage Ace presents a long latency period of 55 min, and a low burst size of only 19 PFU per infected cell, it was showed to have a good lytic activity against the planktonic cells of its host, which makes it a good candidate to be used for biocontrol 12 . The proposed model was used with the faecal content of three healthy donors.…”