Abstract

Salmonella Infantis (SI) is causing a global emerging public health problem associated with poultry production. Its main transmission route to humans is the consumption of contaminated poultry meat, among other food types. Studies reported that SI isolated from humans, broilers, and chicken meat were resistant to multiple antibiotics (MDR). Bacteriophages or lytic phages are viruses that infect and lyse bacteria; these can be used as biocontrol of bacterial load. To characterize the effect of a phage cocktail in human cell cultures (Caco-2) infected with a MDR SI strain. Previously, our laboratory characterized two phages that infected SI MDR (phages: DR91 and DR94) by host range, genome sequencing, and transmission electron microscopy. DR94 (40,000 bp) and DR91 (89,000 bp) are a Myovirus and Tlsvirus, respectively. To evaluate the effect of DR94 on SI adhesion and invasion, cells were infected with MDR SI, and one-hour post-infection were treated with a phage DR94 (MOI 10). Bacterial adhesion and invasion to the cell and phage titer were quantified. To evaluate the activity of DR91 and DR94 in a cocktail (MOI 10) on SI, we used a prophylaxis assay. We observed that SI had adherence to epithelial cells (107 CFU/mL), and after phage DR94 application, this reduced SI adhesion in 7 log10 /mL. We found that SI invades Caco-2 cells (105 CFU/mL) and the further treatment with DR094 reduced SI invasion in 2 log10 /mL. The phage cocktail in prophylaxis assay for two hours showed an important bacterial reduction of 4 log10 /mL in comparison with the control group. The phage titers showed 7 log10 /mL in all assays. Our results support these phages as candidates for cocktails to control salmonellosis in broilers and humans. Further studies are necessary to evaluate the effect of phages on the inflammatory response.