Structure-activity relationship for antibacterial chitosan carrying cationic and hydrophobic moieties

To overcome the problem of antibiotic resistance and toxicity of synthetic polymers, herein we report the synthesis of biocompatible polymers which can serve as broad spectrum antimicrobials. A regioselective synthetic method was developed to synthesize N-functionalized chitosan polymers having similar degree of substitution of cationic and hydrophobic functionality with different lipophilic chains. We obtained optimum antibacterial effect by utilizing the combination of cationic and longer lipophilic chain in the polymer, against four bacterial strains. Inhibition and killing of bacteria were more pronounced in Gram positive bacteria than in Gram negative bacteria. Growth kinetics and scanning electron microscopy imaging of the polymer treated bacterial cells confirmed the inhibition of bacterial growth, morphological changes in the structure and membrane disruption in the cells as compared to the growth control for each strain. Further investigation into the toxicity and selectivity of the polymers guided us to develop a structure-activity relationship for this class of biocompatible polymers.