Enhanced biofilm control through the synergistic action of phages and silver–chitosan-based nanomaterials

The evolution of antimicrobial resistance has dramatically reduced the efficacy of antibiotics used to treat bacterial infections. The formation of biofilms has exacerbated this. Thus, searching for novel therapeutics to treat and prevent antibiotic-resistant biofilm infections is urgent. Therefore, this study aimed to illustrate the synergistic effect of phages and nanoparticles against carbapenem-resistant E. coli and their biofilms. Two lytic phages, namely UGKSEcP1 and UGKSEcP2, which infect diarrheagenic E. coli and UPEC isolated from hospital effluents, and silver nanoparticles biosynthesized in previous studies, were used. Chitosan nanoparticles and chitosan nanoparticles loaded with silver nanoparticles were formulated by the ionic gelation approach. Silver nanoparticles, chitosan, chitosan nanoparticles, and silver–chitosan nanohybrids were analyzed by dynamic light scattering (DLS) technique to determine particle size distribution and zeta potential, X-ray diffraction (XRD) to identify crystalline structure and phase composition, field emission scanning electron microscopy (FESEM) coupled with energy-dispersive X-ray spectroscopy (EDX) to assess surface morphology and elemental composition, and high-resolution transmission electron microscopy (HRTEM) to examine particle size, shape, and nanostructure. Phage viability following exposure to the nanomaterials was assessed using the spot assay, while the combined effects of nanomaterials and phages on E. coli planktonic cells, biofilm treatment, and biofilm inhibition were evaluated by optical density measurements. DLS analysis showed that chitosan nanoparticles and silver–chitosan nanohybrids had surface charges of 22.2 ± 0.44 mV and 54 ± 0.7 mV with PDIs of 0.471 ± 0.034 and 0.534 ± 0.039, respectively. XRD patterns revealed characteristic peaks at 2θ = 19.5° for chitosan nanoparticles and 19.7° for nanohybrids. FESEM and HRTEM analyses indicated spherical morphologies, with HRTEM further estimating average particle sizes of ~ 50 nm for chitosan nanoparticles and ~ 45 nm for the nanohybrids. The combination of phages and nanomaterials markedly suppressed bacterial growth more effectively than either component alone, reducing the bacterial density from approximately 11 log10 CFU/mL to below the log10 limit of detection (LOD). Furthermore, the cocktail of phages and nanomaterials was more effective in preventing biofilm formation than treating it. Based on the findings of this study, a concoction of nanomaterials and phages should be evaluated as candidate therapeutic alternatives to control and treat multidrug-resistant (MDR) and biofilm infections.