Evaluation of zeta potential difference as an indicator for antibacterial strength of low molecular weight chitosan

A set of low molecular weight chitosan (LMWC) products with an intrinsic viscosity-molecular weight (MV) spectrum from 6.9 kDa to 22.4 kDa, with average nanoparticle sizes from 117 nm to 965 nm, were characterized by their zeta potentials and antibacterial activities. The three strains of Staphylococcus aureus and two strains of Escherichia coli exhibited differential sensitivities to LMWCs. Both LMWC adsorption test and antibacterial test results indicated that antibacterial activity was mainly contributed by the difference in zeta potential between the surface of LMWC particles and the bacteria. Scanning electron microscopy (SEM) revealed that LMWC with an MV of 14.8 kDa exerted its antibacterial function by both surface and permeation effects. Once the adsorbed LMWC was washed from the cell wall with an acetate buffer, obvious damages to, and disturbances on, the cell surfaces were observed through SEM.