WaaL–WaaP receptor cross-talk drives phage-induced collateral sensitivity to colistin in Salmonella Pullorum

作者：Mian-Zhi Wang, Yiwen Ren, Lei Jiang, Zi-Xuan Wang, Peng Liu, Mingyi Zhang, Junxuan Zhang, Ruichao Li, Yong-Xue Sun, Zhiqiang Wang · 发表于：Veterinary Research · 年份：2026 · DOI：10.1186/s13567-026-01825-8 · 研究领域：Medicine

Phage therapy typically fails when bacteria rapidly evolve resistance, yet the inevitable fitness costs of escape mutants remain underexploited. In this study, an iterative and targeted phage-cocktail formulation strategy (ITPFS) was presented and developed. A potent lytic phage, PHZ055, was firstly isolated against a colistin-resistant Salmonella Pullorum strain. Co-cultured until resistant mutants emerged, a second lytic phage, PYW047_3, was screened for the resistant variant. The two phages were then combined as a cocktail. Results showed that bacterial growth was strongly suppressed and the emergence of resistance was markedly delayed. Receptor identification revealed that both phages use lipopolysaccharide (LPS) as a receptor, but at distinct sites: PHZ055 targets WaaL, and PYW047_3 targets WaaP. Mutation of WaaL was recently shown to be responsible for the loss of polymerized O-antigen units and thereby exposed the PYW047_3 binding region, indicating that phage cocktails targeting distinct receptor sites can be directionally screened. Moreover, mutants that escaped the two phages not only incurred a growth cost but also exhibited a 32-fold increase in colistin sensitivity. Combining the two phages together with 1/4 MIC colistin almost eradicated all bacteria within 24 h. In all, our study successfully provides a repeatable strategy that incorporates adaptive trade-offs to boost therapeutic efficacy.