Engineering a novel antibacterial agent with multifunction: Protocatechuic acid-grafted-quaternized chitosan

•The grafting of PA onto HACC was achieved by an EDC/NHS coupling method.•PA-g-HACC had a relatively stable structure and chemical composition.•PA-g-HACC own excellent antibacterial properties against E. coli, S. aureus and MRSA.•PA-g-HACC shown favorable antioxidant and anti-inflammatory properties.•The cytocompatibility of PA-g-HACC was improved by appropriate grafting ratio of PA. As a mild cationic antibacterial agent, hydroxypropyltrimethyl ammonium chloride chitosan (HACC) could kill gram-positive bacteria and gram-positive drug-resistant bacteria without cytotoxicity. Nevertheless, it was not effective against gram-negative bacteria. Herein, protocatechuic acid (PA) with broad-spectrum antibacterial properties and pharmacological activities was grafted on HACC. PA-g-HACC showed favourable antioxidant capacity and anti-inflammatory properties. Most importantly, the results of antibacterial assay indicated that the antibacterial rates of all PA-g-HACC groups against Staphylococcus aureus (S. aureus) and methicillin-resistant Staphylococcus aureus (MRSA) were above 92 %, and the antibacterial rate of PA-g-HACC against E. coli was increased with the amount of grafted PA. Furthermore, the cytocompatibility of PA-g-HACC was improved by appropriate grafting ratio of PA, while excessive grafted PA can lead to toxicity. We believe that PA-g-HACC in optimum grafting ratio of PA with favorable antibacterial properties, pharmacological activities and cytocompatibility will be potential antibacterial agent for treating infections.