Bioactivity of chitosan nanoparticles synthesized by a novel route towards Escherichia coli and Bacillus subtilis

Chitosan nanoparticles (CSNP) with an average size of 25.67 nm were synthesized via a novel wet chemical route and characterized using scanning electron microscopy (SEM) and Fourier Transform Infrared (FTIR) spectroscopy. Comparative antibacterial assays of Chitosan NP suspensions prepared in water (at neutral pH) and in dilute acetic acid and chitosan gel prepared in dilute acetic acid/hydrochloric acid (all at concentrations up to 1%) were performed against Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis) bacteria using spread plate method. A parallel viability test was conducted to confirm the presence of surviving cells in the bulk test volume. Minimum bactericidal concentration (MBC) of chitosan gel was 0.5 mg/ml for the bulk chitosan dissolved in 0.05% v/v aq. acetic acid and 0.1 mg/ml for chitosan dissolved in 0.01% v/v aqueous (aq.) hydrochloric acid. In comparison, Chitosan NP were found to be growth promoter at neutral pH and exhibited cell protective efficacy in presence of aq. acetic acid. The biocidal activity of chitosan gel in acidic media was higher when prepared in strong inorganic acid, that is, aq. HCl in comparison with the gel prepared in a relatively weak organic acid that is, aq. CH3COOH at the same concentration. Antibacterial action also showed pH dependence with higher activity at lower pH. However, respective aq. acids also gave comparable bactericidal action; indicating that chitosan may not have any inherent antibacterial property and basically it acts as a growth promoter.