Ecological antagonism constrains receptor-diverse phage cocktail efficacy against multidrug-resistant Enterobacter hormaechei.

Enterobacter hormaechei, a multidrug-resistant member of the Enterobacter cloacae complex, is an important cause of healthcare-associated infections with limited therapeutic options. Here, we isolated and characterized five strictly lytic phages (ΦEAS1, ΦEHO4B, ΦEHO11, ΦEHO14, and ΦECL22) active against multidrug-resistant E. hormaechei. Transposon sequencing combined with targeted gene knockouts demonstrated that phage infection involved multiple bacterial surface structures, including lipopolysaccharide core oligosaccharides, O-antigen, OmpA, and fimbriae, with one phage showing simultaneous multi-receptor dependence. Despite receptor diversity, certain phage combinations displayed antagonistic interactions, indicating that ecological compatibility, rather than receptor complementarity alone, determines cocktail efficacy. Guided by receptor profiling and interaction screening, an optimized four-phage cocktail lysed 86.4% of clinical isolates and effectively suppressed planktonic growth and biofilm formation in vitro. In a murine bacteremia model, phage treatment achieved 100% survival, outperforming Polymyxin B therapy. These findings demonstrate that receptor-diverse phage cocktails can provide robust therapeutic efficacy, but that inter-phage ecological interactions critically constrain optimal design. This study establishes mechanistic principles for rational phage cocktail optimization against multidrug-resistant E. hormaechei.