A Tequintavirus bacteriophage SIA3lw isolated from sewage water with antimicrobial potential against antibiotic-resistant Salmonella Infantis

Salmonella enterica serovar Infantis has consistently contributed to foodborne illness in recent years. Due to frequent antibiotic resistance challenges amid Salmonella species, promising antimicrobial alternatives, such as lytic bacteriophages, are considered to improve the efficacy of the antimicrobial interventions currently used in the food industry. Thus, this study aimed to characterize a new phage from sewage water for its antimicrobial potential against antibiotic-resistant S. Infantis. Salmonella phage vB_SalS-SIA3lw (or SIA3lw) was isolated from sewage water and subjected to genomic and biological characterization. In vitro antimicrobial activity of SIA3lw was determined against two antibiotic-resistant S. Infantis strains. Later, the antibiotic resistance profile of bacteriophage-insensitive mutants (BIMs) was also obtained. The phage has a long, non-contractile tail with a genome size of 116,541 bp and is genomically classified in the Tequintavirus genus, sharing a close evolutionary relationship with Escherichia phage Bf23. However, SIA3lw shared low nucleotide sequence similarities of receptor binding protein (ORF 22) and putative tail fiber protein (ORF 42) genes—both associated with bacterial host recognition and binding—with that in the Bf23. No genes associated with virulence, antibiotic resistance, and lysogeny were found. For biological traits, SIA3lw has a latent period of 30 min and an estimated burst size of 150 PFU/CFU against S. Infantis ATCC BAA-1675. The phage is polyvalent against various S. Infantis and two generic E. coli strains. Among different multiplicity of infections (MOIs), MOI = 100 was the most effective in reducing antibiotic-resistant S. Infantis strains in vitro by more than 4.5 log in 8 h at 25 °C. Despite the occurrence of BIMs, some became sensitive to streptomycin at certain dosages, to which wild-type Salmonella strains were resistant. Most importantly, all selected BIMs were susceptible to the infection by a T4-like phage. Phage SIA3lw has a large burst size and shows strong antimicrobial activities against antibiotic-resistant S. Infantis strains. Although BIMs occur after phage treatment, all BIMs are sensitive to a different phage infection. Most of all, some BIMs trade off their resistance to streptomycin at certain dosages for the development of phage resistance. These findings indicate that the newly isolated Tequintavirus phage SIA3lw has the antimicrobial potential to mitigate antibiotic-resistant Salmonella Infantis.