Bactericidal synergism between phage and antibiotics: A combination strategy to target multidrug-resistant Klebsiella pneumoniae in vitro and in vivo

Bacteriophages have reemerged to potentially replace or complement the role of antibiotics, as bacterial viruses have the ability to inactivate pathogens. However, certain intrinsic limitations of phages overshadow their clinical application, particularly their narrow host spectrum and rapid development of resistance upon treatment. This study aimed to explore the synergistic antimicrobial effect of phage combined with antibiotics against Klebsiella pneumoniae. The time-killing experiments in vitro showed that phage and gentamicin combination displayed synergistic bactericidal activity, leading to a reduction in the minimum inhibitory concentration of gentamicin. Furthermore, the phage HS106/gentamicin combination significantly inhibited biofilm formation and eliminated mature biofilms. On the other hand, phage treatment for 2 h before gentamicin treatment produced better synergistic inhibitory effect. The use of phage followed by gentamicin can effectively inhibit the efflux effect. Surprisingly, the phage HS106/gentamicin combination still exhibited antimicrobial activity against phage-resistant mutants and double-resistant mutants. Finally, the phage HS106/gentamicin combination significantly increased the survival rate of zebrafish infected with K. pneumoniae, indicating its excellent bactericidal activity in vivo. Overall, the phage HS106/gentamicin combination may provide a promising approach for treating infections caused by high-level multidrug-resistant K. pneumoniae.