Novel ε-polylysine/polyethyleneimine -coated Ag nanoparticles for in vitro treatment of Pseudomonas aeruginosa

Pseudomonas aeruginosa is one of the most commonly isolated nosocomial pathogens and is responsible for approximately 10 % of all hospital-acquired infections. P. aeruginosa is difficult to treat with known antibiotics due to its increasing antibiotic resistance. In our study, Ag NPs coated with ε-polylysine (ε-PL) and polyethyleneimine (PEI) were synthesized. These materials showed strong anti- P. aeruginosa capacity at an low concentration (IC50: 7.284 μg/mL). In addition, three drug-resistant clinical strains and biofilm formation were inhibited by ε-PL/PEI-coated Ag NPs (MBIC: 15.63 μg/mL). We further studied the antibacterial mechanism of Ag NPs on different levels and found that a) the amount of reactive oxygen species (ROS) increased, b) the expression of oxidative stress-related genes were up-regulated, c) the activity of total superoxide dismutase decreased, and d) the inhibitory rate is increased on P. aeruginosa cells. These antibacterial effects were dependent on an increasing concentration of Ag NPs but were neutralized by the ROS scavenger N-acetyl-L-cysteine. Therefore, we suggested that oxidative stress induced by ROS is the primary antibacterial mechanism of synthesized Ag NPs.