Abstract
The recent emergence of antibiotic-resistant bacteria requires the development of new antibiotics or new agents capable of enhancing antibiotic activity. Lysozyme degrades bacterial cell wall without involving antibiotic resistance and has become a new antibacterial strategy. However, direct use of native, active proteins in clinical settings is not practical as it is fragile under various conditions. In this study, lysozyme was integrated into chitosan nanoparticles (CS-NPs) by the ionic gelation technique to obtain lysozyme immobilized chitosan nanoparticles (Lys-CS-NPs) and then characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM), which showed a small particle size (243.1 ± 2.1 nm) and positive zeta potential (22.8 ± 0.2 mV). The immobilization significantly enhanced the thermal stability and reusability of lysozyme. In addition, compared with free lysozyme, Lys-CS-NPs exhibited superb antibacterial properties according to the results of killing kinetics in vitro and measurement of the minimum inhibitory concentration (MIC) of CS-NPs and Lys-CS-NPs against Pseudomonas aeruginosa (P. aeruginosa), Klebsiella pneumoniae (K. pneumoniae), Escherichia coli (E. coli), and Staphylococcus aureus (S. aureus). These results suggest that the integration of lysozyme into CS-NPs will create opportunities for the further potential applications of lysozyme as an anti-bacterium agent.
Highlights
Lysozyme degrades certain microorganisms by hydrolyzing the β-1,4 glycosidic linkages between N-acetylmuramic acid and N-acetylglucosamine; these monosaccharides are part of the peptidoglycan of cell wall structure of Gram-positive bacteria [1,2,3]
Lysozyme efficiently immobilized into chitosan nanoparticle showed a small particle size (243.1 ± 2.1 nm), positive zeta potential (22.8 ± 0.2 mV), and great loading efficiency when prepared by ionic gelation technique
No matter incubating at different temperatures or constantly at 37 ◦C for different times, the immobilized lysozyme all showed a higher residual activity than free lysozyme, which means a better thermal stability
Summary
Lysozyme degrades certain microorganisms by hydrolyzing the β-1,4 glycosidic linkages between N-acetylmuramic acid and N-acetylglucosamine; these monosaccharides are part of the peptidoglycan of cell wall structure of Gram-positive bacteria [1,2,3]. It is well known that the overuse and misuse of antibiotics causes bacterial resistance to antibiotics, including resistant P. aeruginosa, S. aureus, and K. pneumoniae Infection with these resistant bacteria can lead to serious life-threatening diseases, such as endocarditis, pneumonia, and sepsis, whereas the lack of effective antibiotics leads to a higher mortality each year [9,10,11]. New antibiotics and other agents that can enhance the antibiotic activity have been developed to address the problem of drug-resistant bacterial infections [12,13]. Most of these new strategies are unsafe and ineffective in defense against drug-resistant bacterial infections. Chitosan performs antimicrobial action in various microorganisms without increasing resistance [20]
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