Isolation and preliminary characterization of bacteriophages for the biocontrol of pathogenic Salmonella enterica strains

With the spread of antibiotic-resistant bacteria, diseases that could once be cured are far less treatable and potentially lethal. Bacteriophages, also known as phages, are viruses that only infect bacteria and “phage therapy” refers to their use as antibacterial agents to control pathogenic bacteria. This project aimed to identify bacteriophages able to infect a set of Salmonella enterica strains isolated from human clinical infections and poultry farms in Zimbabwe. A subset of the available strains was selected to adequately represent multiple strains belonging to four different serovars of the species. The bacteriophages were isolated from environmental samples collected around the city of Padova and in the Venice lagoon by using a plaque assay screen. Host range assays have been performed to further investigate the spectrum of infection of the isolated phages. Selected bacteriophages have been sequenced, and the resulting genomes have been used for taxonomic assignment. Genomic and phylogenetic analyses of the bacterial strains have been conducted in parallel. Bioinformatic analysis of anti-viral defense systems revealed their variation even in closely related S. enterica strains. Further analysis also suggested a possible role of copy number variation of cytochrome C synthesis genes in the bacteriophage resistance of Salmonella Kentucky isolates, as strains with a single copy of ccm(A-E) genes were more susceptible than those with two copies. Finally, host range data were used to design and test in vitro a three-phage cocktail potentially effective against most of the tested S. enterica strains.