Antibacterial effects of chitosan–tripolyphosphate nanoparticles: impact of particle size molecular weight

This study revealed not only the antibacterial potential of smaller chitosan–tripolyphosphate nanoparticles (CS–TPP NPs) over larger ones, but also the attempt has been made to demonstrate antibacterial mechanism of action of CS–TPP NPs on the bacterial cell membrane. Several aspects of low-molecular-weight (LMW) and high-molecular-weight (HMW) CS–TPP NPs were evaluated by their interactions with selected Gram-positive and Gram-negative bacteria. The interaction of CS–TPP NPs with synthetic phospholipid membranes was also evaluated using Fourier transform infrared spectroscopy. The permeabilities of the bacterial outer and inner membranes were evaluated by determining the uptake of a fluorescent probe, 1-N-phenylnaphthylamine, and the release of cytoplasmic β-galactosidase. The morphology of the bacteria treated with LMW and HMW CS–TPP NPs was investigated using transmission electron microscopy. Flow cytometric analysis was also performed for the quantification of dead and surviving bacteria. These studies indicated that the antibacterial effects of LMW CS–TPP NPs (196 and 394 nm) were superior to those HMW CS–TPP NPs (598 and 872 nm). These data indicated that the antibacterial activity of CS–TPP NPs was negatively correlated with particle size and molecular weight, and that CS–TPP NPs represent a promising antimicrobial adjunct.