Bacteriophage-Based Therapeutic, Diagnostic, and Biocontrol Platforms: Engineering, Evidence, and Translational Challenges.

Bacteriophages are being revisited as programmable platforms for therapy, diagnostics, and biocontrol. Their value, however, depends on the setting. Therapeutic phages must do more than lyse bacteria in vitro: they need to reach infection sites, persist long enough to act, reduce bacterial burden, and limit resistance under clinically relevant conditions. Diagnostic platforms are judged by another standard, including sensitivity, specificity, matrix tolerance, and stable signal readout. Food, agricultural, and environmental applications instead rely on formulation stability, host specificity, scalable delivery, and ecological safety. This review summarizes the biological and engineering principles that support phage-based platforms, and then evaluates therapeutic, diagnostic, and nonclinical uses through an application-specific evidence framework. For therapy, we focus on evidence hierarchy, active phage exposure, immune clearance, persistence, infection spread, and host-resistance-bypass phenotypes. Recent studies on high-persistence and hyper-aggressive phages suggest that dissemination, plaque expansion, and resistance-bypass behavior should be considered during early candidate selection. Phage cocktails, antibiotic combinations, and engineered phages remain useful, but they should be treated as adaptive strategies rather than universal solutions. Overall, phage technologies require validation frameworks that link biological function with manufacturing quality, regulatory feasibility, and meaningful clinical or environmental endpoints.