MISC 12. Role of Antibiotic-Loaded Chitosan Nanodroplets on Enterococci Isolated from Chronic Ulcers of the Lower Limbs

The objective of this study was to investigate the effect of a new platform of nanocarriers, called nanodroplets (NDs), to enhance the in vitro activity of vancomycin (Vm) against bacterial colonies isolated from chronic ulcers of the lower limbs. Bacterial isolation and cultures were performed from January 2018 to December 2018. The microorganisms’ growth over time was evaluated in both normoxia and hypoxia. The NDs were supplied loaded with oxygen (oxygen-loaded NDs [OLNDs]), free of oxygen (oxygen-free NDs [OFNDs]), and bound with 320 μg/mL of Vm (Vm-OLNDs, Vm-OFNDs). Minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) were evaluated for Vm, Vm-OLNDs, Vm-OFNDs, OLNDs, and OFNDs in both hypoxia and normoxia. The main end point was to verify whether the MICs of the Vm-NDs were lower than those of Vm alone on bacterial strains. P values < .05 were considered significant. Ten different strains of enterococci (seven Enterococcus faecalis and three Enterococcus faecium) were isolated. The enterococci were able to adapt to hypoxia, and the presence of oxygen in the environment did not influence the MIC of Vm against the strains. All of them showed an MBC/MIC ratio ≥32. Both OFNDs and OLNDs were toxic against the bacteria in hypoxic conditions, but no differences were recorded between OFNDs and OLNDs (all P values > .5). When bounded to Vm, a gain in both the MIC and the MBC was observed for both Vm-OFNDs and Vm-OLNDs but only in Vm-resistant strains and most of all in hypoxic conditions. No differences between Vm-OFNDs and Vm-OLNDs were recorded (all P values > .5). OFNDs, OLNDs, Vm-OFNDs, and Vm-OLNDs showed antibacterial action, with a gain in both MIC and MBC compared with Vm alone, most of all in hypoxic conditions. No differences were recorded in the antibacterial activity between OFNDs and OLNDs or between Vm-OFNDs and Vm-OLNDs.