Abstract
This study attempted to develop chitosan-based nanoparticles with increased stability and antibacterial activity. The chitosan/protamine hybrid nanoparticles were formed based on an ionic gelation method by mixing chitosan with protamine and subsequently cross-linking the mixtures with sodium tripolyphosphate (TPP). The effects of protamine on the chemical structures, physical properties, and antibacterial activities of the hybrid nanoparticles were investigated. The antibacterial experiments demonstrated that the addition of protamine (125 µg/mL) in the hybrid nanoparticles (500 µg/mL chitosan and 166.67 µg/mL TPP) improved the antimicrobial specificity with the minimum inhibitory concentration (MIC) value of 31.25 µg/mL towards Escherichia coli (E. coli), while the MIC value was higher than 250 µg/mL towards Bacillus cereus. The chitosan/protamine hybrid nanoparticles induced the formation of biofilm-like structure in B. cereus and non-motile-like structure in E. coli. The detection of bacterial cell ruptures showed that the inclusion of protamine in the hybrid nanoparticles caused different membrane permeability compared to chitosan nanoparticles and chitosan alone. The chitosan/protamine nanoparticles also exhibited lower binding affinity towards B. cereus than E. coli. The results suggested that the hybridization of chitosan with protamine improved the antibacterial activity of chitosan nanoparticles towards pathogenic E. coli, but the inhibitory effect against probiotic B. cereus was significantly reduced.
Highlights
Antibiotic resistance caused by the overuse of antibiotics has become an important and growing problem all over the world
The antimicrobial activity of chitosan is affected by its molecular weight and degree of acetylation independently [3,22], and the molecular weight has a stronger effect on the antimicrobial activity compared to the degree of acetylation [23,24,25]
It has been reported that decreasing the molecular weight of chitosan may increase its binding affinity to the membrane due to improved mobility, attraction, and ionic interaction [26], though a proper antibacterial activity can be obtained only when the molecular weight is larger than 10 kDa
Summary
Antibiotic resistance caused by the overuse of antibiotics has become an important and growing problem all over the world. According to the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC), the rise of superbugs such as methicillin-resistant. The current strategies used for solving the problem of the growing crisis of antibiotic resistance are mainly centered on the reduction of antibiotic consumption and the development of new antibiotic drugs. The cationic characteristic of chitosan allows it to exhibit superior inhibitory activity against a wide. Factors including molecular weight, deacetylation degree, and positive charge content can affect the antibacterial activities of chitosan [7]. Some studies have modified chitosan with sulfonate groups or quaternary ammonium groups, and integrated antibacterial herbs or enzymes into chitosan-based beads or nanoparticles to improve their antimicrobial activities [8,9,10]
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