Bactericidal effect of polyethyleneimine capped ZnO nanoparticles on multiple antibiotic resistant bacteria harboring genes of high-pathogenicity island

Zinc oxide nanoparticles (ZnO-NP) were synthesized by alcoholic route using zinc acetate as the precursor material and lithium hydroxide as hydrolyzing agent. Further ZnO–PEI NP (derivative of ZnO-NP) was made in aqueous medium using the capping agent polyethyleneimine (PEI). The nanoparticles were characterized by XRD measurements, TEM and other techniques; the weight % of coating shell in the polymer-capped particles was determined by TGA. ZnO–PEI NP is more soluble in water than the uncapped ZnO-NP, and forms a colloidal suspension in water. PEI-capped ZnO-NP exhibited better antibacterial activity when compared with that of uncapped ZnO-NP against a range of multiple-antibiotic-resistant (MAR) Gram-negative bacterial strains harboring genes of high-pathogenicity island. ZnO-NP effectively killed these microorganisms by generating reactive oxygen species (ROS) and damaging bacterial membrane. ZnO–PEI NP at LD50 dose in combination with tetracycline showed synergistic effect to inhibit tetracycline-resistant Escherichia coli MREC33 growth by 80%. These results open up a new vista in therapeutics to use antibiotics (which have otherwise been rendered useless against MAR bacteria) in combination with minimized dosage of nanoparticles for the more effective control of MAR pathogenic bacteria.