Some bacteriophage suspensions have recently been approved and commercialized to control pathogenic bacteria (e.g. Salmonella spp., Escherichia coli, Listeria monocytogenes) in food matrices. However, although Bacillus cereus has been implicated in an increasing number of food outbreaks (e.g. 5.4% in 2013) (EFSA and ECDC, 2015), no phage cocktail has been implemented so far. In particular, food contamination by strains of the emetic pathotype of B. cereus causes nausea and vomiting and, in some severe cases, a liver failure leading to the patient death. Moreover, the ubiquity and sporulation capacity of B. cereus, as well as the extreme resistance (pH, heat and protease) of its emetic toxin, the cereulide, prevent an efficient sanitation by conventional methods. The present work aimed at isolating, from food, animal and environmental matrices, B. cereus-specific bacteriophages in order to control these emetic strains.
From a large collection of bacteriophages isolated from agricultural soils and chicken faeces, six phages preying on B. cereus emetic strains have been retained. Although none were able to lyse the entire set of 155 emetic strains tested, cocktails of these phages could lyse almost 60% of our collection and their application to prevent foodborne intoxications looks particularly promising. Analysis of their genome sequences is under way to confirm the absence of bacterial (pathogenic) genes, and to assure the bone fide virulence nature of these phages (versus mutated temperate phages). In parallel, their morphology and growth parameters have also been investigated in optimal laboratory conditions. Ultimately, a cocktail of these phages will be implemented according to the GRAS status conditions and its efficiency in controlling emetic strains of B. cereus will be evaluated in food matrices, in real life conditions.