# A new Epseptimavirus bacteriophage vB_SalS-SIY1lw as a potential antimicrobial alternative to multidrug-resistant Salmonella Infantis

## TL;DR

A new bacteriophage called SIY1lw, from the Epseptimavirus genus, shows potential as an antimicrobial treatment for multidrug-resistant Salmonella Infantis.

## Contribution

The discovery and characterization of a novel phage, vB_SalS-SIY1lw, with antimicrobial activity against multidrug-resistant Salmonella Infantis.

## Key findings

- SIY1lw is a polyvalent phage effective against S. enterica (Infantis and Newport) and non-pathogenic E. coli.
- The phage reduced S. Infantis strains by 1 and 0.8 log in 6 hours at an MOI of 1,000.
- SIY1lw has a latent period of 30 minutes and a burst size of 42 PFU/CFU.

## Abstract

Salmonella Infantis is an emerging pathogen highly associated with antibiotic-resistant issues and has contributed to increasing foodborne illness in recent years. Thus, finding novel antimicrobial agents is urgent for the solution. The objective was to characterize a newly isolated Epseptimavirus phage with antimicrobial activity against multidrug-resistant S. Infantis strains. Salmonella phage vB_SalS-SIY1lw (or SIY1lw) is a new member of the phages belonging to the Epseptimavirus genus. SIY1lw contained the receptor binding protein (ORF 23) and tail fiber protein (ORF 43) genes—both associated with bacterial host recognition and binding—similar to that in Salmonella phage OSY-STA (the Epseptimavirus genus) and Escherichia phage DaisyDussoix (the Tequintavirus genus), respectively. For biological traits, SIY1lw has a latent period of 30 min and an estimated burst size of 42 PFU/CFU. The phage was polyvalent against S.
enterica (Infantis and Newport) and non-pathogenic E. coli strains. The in vitro antimicrobial activity test showed that the phage with MOI of 1,000 is the most effective in reducing S. Infantis FSIS7823 and FSIS4921 by 1 and 0.8 log, respectively, over the 6-h treatment at 25 °C. These findings indicate that the new Epseptimavirus phage SIY1lw has future potential to develop an antimicrobial alternative to multidrug-resistant S. Infantis strains.

The online version contains supplementary material available at 10.1038/s41598-025-31311-8.