Synergistic Killing and Re-Sensitization of Pseudomonas aeruginosa to Antibiotics by Phage-Antibiotic Combination Treatment

Abstract

Multidrug-resistant (MDR) <i>Pseudomonas aeruginosa</i> infections pose a serious health threat. Bacteriophage-antibiotic combination therapy is a promising candidate for combating these infections. A 5-phage <i>P. aeruginosa</i> cocktail, PAM2H, was tested in combination with antibiotics (ceftazidime, ciprofloxacin, gentamicin, meropenem) to determine if PAM2H enhances antibiotic activity. Combination treatment in vitro resulted in a significant increase in susceptibility of MDR strains to antibiotics. Treatment with ceftazidime (CAZ), meropenem, gentamicin, or ciprofloxacin in the presence of the phage increased the number of <i>P. aeruginosa</i> strains susceptible to these antibiotics by 63%, 56%, 31%, and 81%, respectively. Additionally, in a mouse dorsal wound model, seven of eight mice treated with a combination of CAZ and PAM2H for three days had no detectable bacteria remaining in their wounds on day 4, while all mice treated with CAZ or PAM2H alone had ~10⁷ colony forming units (CFU) remaining in their wounds. <i>P. aeruginosa</i> recovered from mouse wounds post-treatment showed decreased virulence in a wax worm model, and DNA sequencing indicated that the combination treatment prevented mutations in genes encoding known phage receptors. Treatment with PAM2H in combination with antibiotics resulted in the re-sensitization of <i>P. aeruginosa</i> to antibiotics <i>in vitro</i> and a synergistic reduction in bacterial burden <i>in vivo</i>.