Tobramycin-loaded biopolymeric nanoparticles for bacterial biofilms management

The aim of this work was to develop a polymeric drug delivery system able to improve the efficacy of antibiotics against P. aeruginosa (Pa) biofilms, the main respiratory pathogen in adult patients with cystic fibrosis. Tobramycin (Tb)-loaded biopolymeric nanoparticles based on dextran sulphate (DS) and chitosan (CS) were prepared by ionotropic gelation. Tb content in CS/DS nanoparticles was measured by using an indirect spectrophotometric method. Tb in vitro release was studied by suspending a fixed amount of nanoparticles in PBS (pH 7.4) at 37°C and withdrawing samples at fixed time intervals. Antibiotic efficacy was tested on Pa biofilms and compared to free drug. We optimized Tb entrapment in DS/CS nanoparticles, obtaining particles of 170 nm and with a drug loading of 400 µg/mg. Such preparations were able to release approximately 25% of their cargo in 60 hours. Tb-loaded nanoparticles were tested on 2 days old P. aeruginosa biofilms and compared to free Tb. We obtained a reduction of the biofilm biomass using either free Tb or Tb-loaded nanoparticles, however the fraction of surviving bacteria was lower in samples treated with Tb-loaded nanoparticles in respect to those treated with an equal amount of free antibiotic. It is well known that bacterial biofilms are less susceptible to antibiotic treatment compared to planktonic cells, although the mechanisms are still poorly understood. We showed that engineered nanoparticles with mucoadhesive properties, entrapping tobramycin, are more efficient in biofilm eradication than free drug.