Sub-therapeutic Concentrations of Antibiotics Induce Prophage-driven Superinfection Exclusion and Fitness Cost in Pseudomonas aeruginosa

Bacteria and other microbes can naturally produce antibiotics within their native soil environment, but often at sub-inhibitory concentrations; consequently, the exact role of antibiotics within bacterial native communities remains unknown. We have shown that subtherapeutic quantities of naturally occurring antibiotics can induce the Pseudomonas prophage Pf4, and superinfection of Pseudomonas aeruginosa cells by this phage leads to their reduced virulence, as demonstrated by impaired twitching motility, compromised macrophage evasion, and increased killing by macrophages in vitro. Thus, the production of subtherapeutic concentrations of antibiotics by environmental microbes may provide the producers an evolutionary advantage associated with reduced fitness induced by prophages in the competing bacteria. Collectively, these results reveal the role of naturally occurring antibiotics in altering fitness by phage-mediated superinfection exclusion and provide potential clinical implications in the application of phage therapy. Significance StatementThis study provides insights into the mechanisms by which sub-inhibitory concentrations of environmentally-produced antibiotics induce Pseudomonas aeruginosa prophages, revealing a potential evolutionary strategy for competitive advantage among bacteria. By activating prophages, antibiotics can induce fitness defects in neighboring bacteria, impacting their motility, phagocytosis, and survival within macrophages. Such previously unrecognized role for environmental antibiotics in bacterial ecosystems may offer insights into enhancing phage therapy by exploiting phage-antibiotic synergies. Understanding phage-host interactions can enhance therapeutic strategies to mitigate bacterial infections and antimicrobial resistance.