Abstract

Salmonella Infantis (SI) is causing a global emerging public health problem attributed mainly to contaminated poultry meat, among other food types. Bacteriophages or lytic phages are viruses that infect and lyse bacteria with the potential to be used as biocontrol of bacterial contamination. Previously, our laboratory characterized two phages F1 (Myovirus) and F2 (Tlsvirus) that infected SI-MDR strains. Characterization includes genome sequencing, host range, and transmission electron microscopy. Our aim was to evaluate the effect of a phage cocktail (F1 and F2) on human colon cell cultures (Caco-2) infected with a SI-MDR strain, using prophylaxis (PA), remedial (RA) and bacterial invasion assays. In the PA, cells were treated with F1 and F2 (MOI 10), during 30, 60, and 120 minutes; later, cells were infected with SI-MDR for one-hour. To evaluate RA, cells were infected with SI-MDR, and one-hour post-infection were treated with F1 or F2 (MOI 10) for one hour. To evaluate the bacterial invasion, cells were infected with SI-MDR, and one-hour post-infection were treated with 100 g/mL of gentamycin for one hour. Later, cells were treated with F1 or F2 (MOI 10) for one hour. Bacterial adhesion and invasion to confluent cells and phage titer were quantified by colony forming unit (CFU) and plaque forming unit (PFU) count. Assays were performed in two biological replicates with duplicate wells. In PA, the phage cocktail for two hours showed a significant bacterial reduction of 4 log10/mL in comparison with infected cells (SI-MDR). In the RA, we observed that SI-MDR had adherence to epithelial cells (107 CFU/mL), and after phage application the SI-MDR adhesion was reduced in 5 log10/mL for F1 and 7 log10/mL for F2. In the bacterial invasion evaluation, we found that SI-MDR invades Caco-2 cells (104 CFU/mL), and phage treatment reduced SI invasion in 2 log10/mL for F2 and 4 log10/mL for F1 phage. In PA, RA and bacterial invasion assays, we recovered high titers of phages at all times points. Our results support that phages F1 and F2 could be use as candidates for therapeutical control of salmonellosis in human culture cells using a prophylaxis approach.