Abstract
The well-known antimicrobial effects of chitosan (CS) polymers make them a promising adjuvant in enhancing antibiotic effectiveness against human pathogens. However, molecular CS antimicrobial mechanisms remain unclear, despite the insights presented in the literature. Thus, the aim of the present study was to depict the molecular effects implicated in the interaction of low or medium molecular mass CS polymers and their nanoparticle-counterparts against Escherichia coli. The differential E. coli proteomes sensitized to either CS polymers or nanoparticles were investigated by nano liquid chromatography–mass spectrometry (micro-LC-MS/MS). A total of 127 proteins differentially expressed in CS-sensitized bacteria were predominantly involved in (i) structural functions associated to the stability of outer membrane, (ii) increment of protein biosynthesis due to high abundance of ribosomal proteins and (iii) activation of biosynthesis of amino acid and purine metabolism pathways. Antibacterial activity of CS polymers/nanoparticles seems to be triggered by the outer bacterial membrane disassembly, leading to increased protein biosynthesis by diverting the metabolic flux to amino acid and purine nucleotides supply. Understanding CS-antibacterial molecular effects can be valuable to optimize the use of CS-based nanomaterials in food decontamination, and may represent a breakthrough on CS nanocapsules-drug delivery devices for novel antibiotics, as the chitosan-disassembly of bacteria cell membranes can potentialize antibiotic effects.
Highlights
Chitosan (CS) is a well-known polycationic biopolymer that offers multiple benefits in many novel applications, since it allows for complexation with natural antibiotics, antioxidants, proteins and dyes [1,2]
Previous studies have suggested various mechanisms to explain the mode of action leading to chitosan antimicrobial activity [6,7,8].The most explored is the intracellular leakage hypothesis, where bacterial membrane permeability is altered by the interaction between positively-charged-CS and negatively-charged bacterial surfaces, resulting in the loss of cytosolic components through the damaged plasma membrane, leading to cell death [6]
The dskA participates in the stringent response, a reprogramming of cell metabolism in response to environmental stressors [40,41]. This stringent response leads to the repression of genes required for rapid growth, in order to save ATP and precursors for the biosynthetic pathways necessary to maintain life under unsuitable stress growth conditions, such as the activation of genes involved in amino acid biosynthesis, nutrient acquisition and stress survival, in accordance to the results described [41]
Summary
Chitosan (CS) is a well-known polycationic biopolymer that offers multiple benefits in many novel applications, since it allows for complexation with natural antibiotics, antioxidants, proteins and dyes [1,2]. Previous studies have suggested various mechanisms to explain the mode of action leading to chitosan antimicrobial activity [6,7,8].The most explored is the intracellular leakage hypothesis, where bacterial membrane permeability is altered by the interaction between positively-charged-CS and negatively-charged bacterial surfaces, resulting in the loss of cytosolic components through the damaged plasma membrane, leading to cell death [6]. This theory was reinforced by studies investigating CS microparticles, interactions with specific targets hypothesized to be the surface-exposed proteins. CS antimicrobial activity has been observed, in acidic pH, and at neutral pH (i.e., 7.0) [10]
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