Antagonistic effect of kanamycin on kanamycin-resistant Escherichia coli infection by BtuB-targeting bacteriophages.

In combined treatments with antibiotics and bacteriophages (phages), antibiotics have the potential to influence phage infectivity, exhibiting effects that vary from synergistic to antagonistic. Here, we investigated the effects of various classes of antibiotics on Escherichia coli infection by phages that use different receptors, including vitamin B₁₂ outer membrane transporter (BtuB), lipopolysaccharide (LPS), outer membrane protein A (OmpA), and nucleoside-specific porin (Tsx). Among the antibiotics tested, ampicillin did not affect phage infection, whereas colistin, chloramphenicol, and tetracycline inhibited phage infection irrespective of the phage receptor. In contrast, kanamycin inhibited infection of kanamycin-resistant E. coli by the BtuB-targeting phages, but not by the phages using LPS, OmpA, or Tsx. The receptor-specific antagonistic effect of kanamycin on BtuB-targeting phage infection was stronger than the effect observed with colistin, chloramphenicol, or tetracycline. When using a btuB-knockout mutant, we observed reduced kanamycin accumulation and increased kanamycin resistance compared to wild-type E. coli, suggesting that BtuB might be involved in kanamycin uptake. These results suggest that the antagonism between kanamycin and BtuB-targeting phage infection may be linked to the role of BtuB in facilitating kanamycin uptake. This study shows that the antimicrobial activity of phage-antibiotic combinations may be phage-receptor-specific, highlighting the need to consider phage receptors when selecting optimal combinations for effective phage therapy.