Antibacterial activity of quaternary ammonium-containing chitosan particles

Abstract

This research aims to develop environmentally friendly, organic antibacterial fillers from quaternary ammonium-containing chitosan particles that may be applicable for biomedical device, health, and textile industries. Quaternary ammonium-containing chitosan particles were prepared by two methods. The first method was to prepare chitosan particles by ionic crosslinking. Their surface was then modified by heterogeneous quaternization through N-reductive alkylation with aldehyde followed by alkylation with alkyl iodide or direct methylation with methyl iodide. The second method was to synthesize N,N,N-trimethyl chitosan by homogeneous quaternization using methyl iodide followed by particle formation. As analyzed by FT-IR, 1H NMR, PCS, and TEM, sub-micron, spherical, and positively charged quaternized chitosan particles were formed. Antibacterial activity tests were performed by turbidimetric method and viable cell counts. All quaternized chitosan particles exhibited superior antibacterial activity against, S. aureus, the gram-positive bacteria, to the native chitosan particles at neutral pH. This may be explained as a result of ionic binding between the positive charges on the particles and the negatively charged teichoic acid on the outer membrane of S. aureus. Only some quaternized chitosan particles, especially those having high charge density and bearing large alkyl substituents, were capable of suppressing the growth of E. coli, the gram negative bacteria, of which outer membrane contains lipopolysaccharide. The inhibitory efficiency quantified by minimum inhibitory concentration was also found to be dose-dependent.