Study on the therapeutic index and synergistic effect of Chitosan-zinc oxide nanomicellar composites for drug-resistant bacterial biofilm inhibition.

The synergistic effectiveness of chitosan with zinc oxide nanomicelles (CZNPs) on broad spectrum of multidrug resistance (MDR) was previously evidenced in our labs, requiring elucidation of the therapeutic index (TI) for safe in vivo use. This in vitro assessment estimated the effective dose (ED 50) of micellar CZNPs for eradication of the MDR Enterococcus faecium 1449 model and the corresponding cytotoxic dose (LD 50) against rat small intestinal epithelial cells as functions of TI. In order to visually determine the mechanistic effects of micellar CZNPs on bacterial biofilm size reduction, LIVE/DEAD viability assay was used in conjunction with advanced fluorescence imaging and 3D confocal microscopy. Biofilm quantification was performed through the measure of the fluorescence intensity, using the Biotek Synergy Neo2 for calculating the ED 50. To generate the LD 50 , the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cytotoxicity assay was implemented. Quantification results revealed, at the same concentration (200 µg/mL), micellar CZNPs had average biofilm reduction of approximately 50.22% at 24 h (ED 50 = 199.13 µg/mL, LD 50 = 240.20 µg/mL, TI = 1.2062), compared to chitosan (15.66%) and ZnO (13.94%) alone. Conclusively, the ED 50 of micellar CZNPs on MDR bacterial biofilms (199.13 µg/mL) as a function of TI reveals a promising nanotherapeutic agent in comparison to either Chitosan or ZnO alone. [ABSTRACT FROM AUTHOR]