Effect of time of therapy with wild-type lytic bacteriophages on the reduction of Salmonella Enteritidis in broiler chickens.

Salmonella Enteritidis remains a leading cause of human foodborne disease, mostly associated with the consumption of contaminated poultry products. To more strategically implement a phage therapy scheme for S. Enteritidis control in broilers, a cocktail containing three wild-type lytic bacteriophages (LBs) previously isolated from chickens was evaluated shortly and later after a challenge. Genomic characterization, lytic spectrum and in vitro efficacy were determined for each studied LB. In independent trials, broilers challenged with S. Enteritidis on day of hatch received phage therapy from 6 to 10 days of age (early treatment), and from 31 to 35 days of age (later treatment). S. Enteritidis analyses were performed before treatment and at 1, 4, 7 and 10 days post-treatment (dpt) in both trials. Partial DNA sequence analysis of each LB revealed close similarity to the Ackermannviridae family. LBs lysed different Salmonella enterica serovars, while other tested bacteria were refractory. An in-vitro reduction of 1.49, 0.65 and 0.58 log CFU/mL in S. Enteritidis number was obtained after co-incubation for 3 h with each LB. Both in vivo trials showed a significant reduction in the average number of intestinal S. Enteritidis calculated after phage therapy compared with controls. However, the highest efficiency was found in the later therapy, which resulted in a reduction of 1.08 log CFU/g in the average from 4 to 10 dpt, showing potential for future use as a pre-harvest strategy to reduce the S. Enteritidis intestinal colonization in broilers on farms.