Salmonella is one of the main causes of foodborne diseases related to poultry product consumption and is a public health concern. The use of lytic bacteriophages could be a novel, safe and effective approach, to reduce the prevalence of Salmonella in poultry and subsequently reduce the incidence of foodborne salmonellosis in humans.

This study evaluates the prophylactic and therapeutic effect of phages, administered via drinking water, on Salmonella levels in chickens. A cocktail of 6 lytic phages with demonstrated in vitro efficacy against various Salmonella serotypes was used.

First, the phages were demonstrated to persist in chickens' gut for at least 3 days without Salmonella challenge. The prophylactic potential of the cocktail was then evaluated in vivo. Fifty chicks were challenged by oral gavage with Salmonella Enteritidis LA5 at 5x104 CFU/chick at 7 days of age. Phages were administrated before the challenge via drinking water during the first 6 days of the chicks' life and 2 days prior to the end of the trial to check emerging resistance. The ability of resistant clones to colonize chicks was also studied. The therapeutic potential of the cocktail was also evaluated by giving phages at the end of the trial to decrease carcass contamination at slaughter. During the different trials, Salmonella enumeration and phage identification and counting were investigated.

Results showed that up to 4 days post infection, phages had a preventive effect and they significantly (P<0.05) reduced Salmonella colonization in ceca and feces by 2 to 4 logs. Salmonella levels increased 7 days post infection, after phage treatment was stopped. During this period, only 2 out of 6 phages were detected in the different gut segments. Salmonella resistance was observed only against these persistent phages and resistant clones recovered shown a reduced colonization capacity in chickens' gut. No resistance was observed against the other phages. Indeed, resumption of phage administration 2 days before the end of the trial reduced the Salmonella loads again by 1 log in the ceca. In parallel, the therapeutic use of phages reduced Salmonella cecal level by 4 logs compared to the situation before phage administration.

This treatment showed encouraging results regarding the effect of phages on Salmonella levels in chickens during critical steps of poultry production. Future work will be to study the mechanisms of resistance acquired by Salmonella in vivo and also the impact of this treatment on the chicken's microbiota.