Characterization of the selective binding of modified chitosan nanoparticles to Gram-negative bacteria strains

Chitosan is a nature-sourced polysaccharide widely used in numerous applications. The antibacterial potential of chitosan has attracted researchers to further develop and utilize this polymer for the formation of biocompatible antibacterial agents for both the food and healthcare industries. The tested hypothesis in this study is that modified N-alkylaminated chitosan nanoparticles (CNPs) have selective binding properties to Gram-negative bacteria strains that result in bacterial aggregation. Various bacterial strains were tested of five Gram-negative bacteria including Erwinia carotovora, Escherichia coli, Pseudomonas aeruginosa, Salmonella, and Serratia marcescens, as well as three Gram-positive bacteria strains including Bacillus licheniformis, Bacillus megaterium, and Bacillus subtilis. The fluorescence microscopy characterization showed that the presence of CNPs caused the aggregation of Escherichia coli bacteria cells, where modified CNPs with a shorter chain length of the substituent caused a higher aggregation effect. Moreover, it was found that the CNPs exhibited a selective binding behavior to Gram-negative as compared to Gram-positive bacteria strains, mainly to Escherichia coli and Salmonella. Also, the scanning electron microscopy characterization showed that CNPs exhibited selective binding to Gram-negative bacteria, which was especially understood when both Gram-negative and Gram-positive bacteria strains were within the same sample. In addition, the bacterial viability assay suggests that CNPs with a lower degree of substitution have a higher inhibitory effect on bacterial growth. CNPs with longer side chains had a less inhibitory effect on the bacterial growth of Gram-negative strains, where a concentration-dependent response pattern was only seen for the cases of Gram-negative strains, and not for the case of Gram-positive strain. To conclude, the further understanding of the selective binding of CNPs to Gram-negative bacteria strains may produce new opportunities for the discovery and characterization of effective antibacterial agents.