Impact of <i>Pseudomonas aeruginosa</i> biofilm exopolysaccharide composition on bacteriophage and bacteriophage-antibiotic combination activity

Multidrug-resistant <i>Pseudomonas aeruginosa</i> is a leading cause of hospital-acquired infections, including medical device infections, partially due to the organism's ability to produce biofilm on prosthetic material. Increased antibiotic tolerance of bacteria within biofilm, along with the increasing prevalence of infections caused by multidrug-resistant <i>P. aeruginosa</i>, including extensively drug-resistant phenotypes, results in scenarios where conventional antibiotics may fail to effectively treat these infections. Bacteriophage (phage) therapy is a promising alternative to conventional antimicrobial therapy that can provide potent antibiofilm activity, particularly when combined with antibiotics. The impact of <i>P. aeruginosa</i> biofilm phenotype on the efficacy of phage-antibiotic combinations remains unclear. We characterized the biofilms of a panel of 10 clinical and two laboratory <i>P. aeruginosa</i> isolates by determining the minimum biofilm inhibitory concentrations, biofilm production capabilities, and phage activity. Furthermore, we quantified the exopolysaccharide content of <i>P. aeruginosa</i> strains PAO1 and PA14 and confirmed they produced Class II and Class I biofilm, respectively. We then selected a triple-phage cocktail with broad activity across all <i>P. aeruginosa</i> strains for evaluation of antibiofilm activity against PAO1 and PA14 <i>in vitro</i>. Through spectrophotometric growth suppression and time-kill analyses, we found the triple-phage cocktail + ciprofloxacin to be more efficacious in biofilm eradication than either modality alone. Phage 109 displayed potent antibiofilm activity against both strains irrespective of planktonic activity, whereas phages E2005-C and EM-T3762627-2_AH displayed distinct antibiofilm activity based on biofilm phenotype. These data warrant further investigation into the impact of <i>P. aeruginosa</i> biofilm phenotype on phage antibiofilm activity.