In vitro activity of cefiderocol against Gram-negative aerobic bacilli in planktonic and biofilm form-alone and in combination with bacteriophages

Abstract

Multi-drug resistant Gram-negative pathogens are increasingly difficult-to-treat perpetrators of infections. New, innovative, and more multifaceted therapies for the treatment of multi-drug resistant strains are thus urgent to hinder further drug resistance and mitigate deadly, untreatable infections. Our study aimed to investigate the efficacy of cefiderocol against Gram-negative aerobic bacteria alone and in combination with phages. The minimum inhibitory concentration (MIC) of cefiderocol was determined using the microdilution broth method, while the minimum biofilm bactericidal concentration was assessed using isothermal microcalorimetry. The combined effect of cefiderocol and phages was evaluated using colony-forming unit counts. Results demonstrated a notable antibacterial effect of cefiderocol, with 83.4% of tested strains exhibiting susceptibility. When combined with phages, the MIC of cefiderocol was reduced by 2-64-fold, indicating a synergistic interaction between the two agents. Furthermore, the combination therapy showed enhanced efficacy against biofilm compared to monotherapy with either cefiderocol or phages alone, leading to complete biofilm elimination in certain cases. This study highlights the potential of combining cefiderocol with phages as a strategy to combat multi-drug resistant Gram-negative bacterial infections. The observed synergy suggests that this combination therapy could improve treatment outcomes and help address the challenges of antibiotic resistance and biofilm-associated infections.

Keywords: Anti-biofilm activity; Cefiderocol; Multi-drug resistant pathogens; Phages.

Fig. 1

Calorimetric curves. Monitored heat flow (µW) of E. coli 1, 2, 3, K. pneumoniae 1, 2, 3, P. aeruginosa 1, 2, 3, and A. baumannii 1, 2, 3 biofilms treated with cefiderocol at different concentrations (16, 32, 64, 128, 256, 512, and 1024 µg/mL) as monotherapy. Each curve shows the heat flow produced over time by remaining viable bacteria in the biofilm after 24 h treatment. GC represents the growth control sample not exposed to any antimicrobials. Data of a representative experiment are reported.

Fig. 2

Phage-cefiderocol synergy. Synograms represent the mean reduction percentage of each treatment from three biological replicates: Reduction (%) = [(Odgrowthcontrol – ODtreatment)/ODgrowthcontrol] x 100. The regions between the solid lines represent the interacting regions of the phage and antibiotic, and the regions below the solid lines indicate phage and antibiotic alone.

Fig. 3

Anti-biofilm effect of cefiderocol-phage combination. Each column represents the CFU of remaining viable bacteria within the biofilm after 24 h of treatment with cefiderocol alone at 100 µg/mL, phage alone at 10⁸ PFU/mL, or cefiderocol-phage combinations. Error bars represent the standard deviation (SD) of the mean. CFD, cefiderocol; Φ, bacteriophage; GC, growth control. Data represent mean ± SD (n = 6). ***, p < 0.001; **, p < 0.01; *, p < 0.05.