A Salmonella phage steers bacterial populations toward hypersensitivity to benzalkonium chloride, hydrogen peroxide, and triclosan

ABSTRACT Phage steering is an emerging antimicrobial strategy that exploits the evolutionary consequences of phage predation to sensitize bacterial populations to existing antimicrobials. While phage steering toward hypersensitivity to antibiotics and immune effectors has been well documented, little is known about whether a similar mechanism can enhance bacterial sensitivity to commercial disinfectants. Here, we show that SF1, a lytic siphovirus infecting Salmonella enterica , requires an intact O-antigen layer for adsorption and lytic replication, and that in-frame deletion mutants with O-antigen or deeper LPS defects had increased susceptibility to several commercial disinfectants. Critically, SF1 enhanced the activity of all disinfectants tested in combination assays and, moreover, exhibited mathematical synergy with benzalkonium chloride, hydrogen peroxide, and triclosan, compounds to which SF1-selected LPS mutants were hypersensitive. These findings are consistent with the hypothesis that SF1 functions not only as a bactericidal agent, but as an evolutionary steering tool that potentiates sanitizer activity through selection for sanitizer-hypersensitive phenotypes. Broadly, these results support phage steering as a promising strategy for deploying bacteriophages as adjuvants to commercial disinfectants. IMPORTANCE Commercial disinfectants are essential for controlling pathogens throughout the food production and processing chain, but their effectiveness is increasingly compromised by bacterial tolerance and persistence. Although bacteriophages are being investigated as direct bactericidal agents, their utility as adjuvants to commercial sanitizers remains underexplored. In this study, we demonstrate that Salmonella phage SF1 selects for LPS-deficient mutants that exhibit increased susceptibility to several commercial disinfectants. Importantly, we further show that SF1 synergizes with sanitizers to which phage-selected mutants are hypersensitive, supporting a steering-mediated mechanism whereby phage predation enhances sanitizer activity. To our knowledge, this is the first report demonstrating phage steering as a strategy for deploying bacteriophages as synergizing adjuvants to commercial disinfectants. These findings highlight the potential value of exploiting evolutionary trade-offs to improve pathogen control in food processing environments.