Pyoverdine-antibiotic combination treatment: its efficacy and effects on resistance evolution in Escherichia coli

Antibiotic resistance is a growing concern for global health, demanding innovative and effective strategies to combat pathogenic bacteria. Pyoverdines, iron-chelating siderophores produced by environmental Pseudomonas spp., present a novel promising approach to induce growth arrest in pathogens through iron starvation. While we have previously demonstrated the efficacy of pyoverdines as antibacterials, our understanding of how these molecules interact with antibiotics and impact resistance evolution remains unknown. Here, we investigate the propensity of different Escherichia coli variants to evolve resistance against pyoverdine, the cephalosporin antibiotic ceftazidime, and their combination. We found that strong resistance against ceftazidime and weak resistance against pyoverdine evolved in the wildtype E. coli strain under single and combination treatment. Ceftazidime resistance was linked to mutations in outer membrane porin genes (envZ and ompF), whereas pyoverdine resistance was associated with mutations in the oligopeptide permease (opp) operon. In contrast, resistance phenotypes were attenuated under combination treatment, particularly in an E. coli strain carrying a costly multicopy plasmid. Altogether, our results show that pyoverdine as an antibacterial is particularly potent and evolutionarily robust against plasmid-carrying E. coli strains, presumably because iron starvation compromises both cellular metabolism and plasmid replication.