Antimicrobial Activity Of Chitosan Research Articles

Antibacterial action of a novel functionalized chitosan-arginine against Gram-negative bacteria

The antimicrobial activity of chitosan and chitosan derivatives has been well established. However, although several mechanisms have been proposed, the exact mode of action is still unclear. Here we report on the investigation of antibacterial activity and the antibacterial mode of action of a novel water-soluble chitosan derivative, arginine-functionalized chitosan, on the Gram-negative bacteria Pseudomonas fluorescens and Escherichia coli. Two different arginine-functionalized chitosans (6% arginine-substituted and 30% arginine-substituted) each strongly inhibited P. fluorescens and E. coli growth. Time-dependent killing efficacy experiments showed that 5000 mg l −1 of 6%- and 30%-substituted chitosan-arginine killed 2.7 logs and 4.5 logs of P. fluorescens, and 4.8 logs and 4.6 logs of E. coli in 4 h, respectively. At low concentrations, the 6%-substituted chitosan-arginine was more effective in inhibiting cell growth even though the 30%-substituted chitosan-arginine appeared to be more effective in permeabilizing the cell membranes of both P. fluorescens and E. coli. Studies using fluorescent probes, 1- N-phenylnaphthylamine (NPN), nile red (NR) and propidium iodide (PI), and field emission scanning electron microscopy (FESEM) suggest that chitosan-arginine’s antibacterial activity is, at least in part, due to its interaction with the cell membrane, in which it increases membrane permeability.

Hydrophobization and Antimicrobial Activity of Chitosan and Paper-Based Packaging Material

This study reports the elaboration of water-resistant, antimicrobial, chitosan and paper-based materials as environmentally friendly food packaging materials. Two types of papers were coated with chitosan-palmitic acid emulsions or with a blend of chitosan and O,O'-dipalmitoylchitosan (DPCT). Micromorphology studies showed that inclusion of hydrophobic compounds into the chitosan matrix was enhanced by grafting them onto chitosan and that this led to their penetration of the paper's core. Compared to chitosan-coated papers, the coating of chitosan-palmitic emulsion kept vapor-barrier properties unchanged (239 and 170 g.m(-2).d(-1) versus 241 and 161 g.m(-2).d(-1)), while the coating of chitosan-DPCT emulsion dramatically deteriorated them (441 and 442 g.m(-2).d(-1)). However, contact angle measurements (110-120 degrees after 1 min) and penetration dynamics analysis showed that both strategies improved liquid-water resistance of the materials. Kit-test showed that all hydrophobized chitosan-coated papers kept good grease barrier properties (degree of resistance 6-8/12). Finally, all chitosan-coated materials exhibited over 98% inhibition on Salmonella Typhimurium and Listeria monocytogenes .

Chitosan-Copper (II) complex as antibacterial agent: synthesis, characterization and coordinating bond- activity correlation study

The antimicrobial activity of chitosan is unstable and sensitive to many factors such as molecular weight. Recent investigations showed that low molecular weight chitosan exhibited strong bactericidal activities compared to chitosan with high molecular weight. Since chitosan degradation can be caused by the coordinating bond, we attempt to synthesize and characterize the chitosan-Cu (II) complex, and thereafter study the coordinating bond effect on its antibacterial activity against Salmonella enteritidis. Seven chitosan–copper complexes with different copper contents were prepared and characterized by FT-IR, UV-vis, XRD and atomic absorption spectrophotometry (AAS). Results indicated that for chitosan-Cu (II) complexes with molar ratio close to 1:1, the inhibition rate reached 100%.

Antimicrobial activity of chitosan against Campylobacter spp. and other microorganisms and its mechanism of action.

The antimicrobial activities of three chitosans with different molecular masses against six gram-negative and three gram-positive bacteria were examined. Campylobacter spp. were the microorganisms most sensitive to chitosan, regardless of their molecular mass. The MIC of chitosan for Campylobacter ranged from 0.005 to 0.05%, demonstrating the global sensitivity of campylobacters to chitosan. Chitosan caused a loss in the membrane integrity of Campylobacter, measured as an increase in cell fluorescence due to the uptake of propidium iodide, a dye that is normally excluded from cells with intact membranes. As cells entered the stationary phase, there was a change in cell membrane resistance toward a loss of integrity caused by chitosan. This study demonstrates that chitosans could be a promising antimicrobial to control Campylobacter.

Changes in microbial flora of Pacific oysters ( Crassostrea gigas) during refrigerated storage and its shelf-life extension by chitosan

Changes in microbial flora of Pacific oysters ( Crassostrea gigas) during storage at 5 ± 1 °C were analyzed and the antimicrobial activity of chitosan was studied to identify its potential in shelf-life extension. The dominant microorganisms were found to be Pseudomonas (22%) and Vibrionaceae (20%) in raw oysters. During storage, proportion of Pseudomonas increased significantly and reached 73% at the end of storage, while Vibrionaceae preserved a level of approximate 20%. Wide-spectrum antibacterial property of chitosan against the bacteria isolated from oysters was discovered, and chitosan concentration of 5.0 g/L was eventually determined for application in oyster preservation. Based on microbiological analysis, biochemical indices determination and sensory evaluation, shelf-life of oysters stored at 5 ± 1 °C was determined. Data showed that chitosan treatment extended the shelf-life of oysters from 8–9 days to 14–15 days.

Antimicrobial activity and physical properties of chitosan–tapioca starch based edible films and coatings

Abstract Antimicrobial activity of edible coating solutions based on chitosan and blends of chitosan–tapioca starch with or without potassium sorbate (KS) addition was studied. The agar well diffusion assay showed an antagonist effect on the efficiency of chitosan against Lactobacillus spp. when KS and/or tapioca starch were present. A salmon slice coating assay showed that the chitosan solution was the best coating since aerobic mesophilic and psychrophilic cell counts were reduced, pH and weight loss remained acceptable throughout refrigerated storage, extending global quality to 6-days. Chitosan–tapioca starch based films reduced Zygosaccharomyces bailii external spoilage in a semisolid product but were not effective against Lactobacillus spp. The results suggest that antibacterial action depended on the application technique, due to the fact that chitosan is more available in a coating solution than in a film matrix. Interactions between chitosan–starch and/or KS could affect film physical properties and the antimicrobial activity of chitosan. The addition of chitosan reduced water vapor permeability and solubility of starch films.

Antimicrobial activity of chitosan against vibrios from freshwater prawn Macrobrachium rosenbergii larval rearing systems

Chitosan is a biocompatible and biodegradable natural polymer with established antimicrobial properties against specific microorganisms. The present study demonstrates its antibacterial activity against 48 isolates of Vibrio species from prawn larval rearing systems. The antibacterial activity had a positive correlation with the concentration of chitosan. This work opens up avenues for using chitosan as a prophylactic biopolymer for protecting prawn larvae from vibriosis.

Chitosan: antimicrobial activity, interactions with food components and applicability as a coating on fruit and vegetables

Chitosan has recently gained more interest due to its applications in food and pharmaceutics. Among others, the antimicrobial activity of chitosan has been pointed out as one of its most interesting properties of chitosan. The aim of this study was threefold: (1) the quantification of the antimicrobial effect of chitosan with a deacetylation degree of 94% and a molecular weight of 43 kDa on different psychrotrophic spoilage organisms and food pathogens. (2) The determination of the influence of different food components (starch, whey protein, NaCl and oil) on the antimicrobial effect of chitosan and (3) the investigation of the effects of chitosan coatings on controlling decay of minimally processed fruits and vegetables (strawberry and lettuce). For the first aim several bacteria and yeast were exposed to chitosan concentrations varying from 40 to 750 mg/l. Generally, Gram-negative bacteria seemed to be very sensitive for the applied chitosan (MIC⩽0.006% (w/v)) while the sensitivity of Gram-positive bacteria was highly variable and that of yeast was intermediary (0.01% (w/v)). To achieve the second aim, the media, with one of these components added, were inoculated with Candida lambica (±2 log cfu/ml) and were incubated at 7°C until the yeast reached the stationary phase. Starch, whey proteins and NaCl had a negative effect on the antimicrobial activity. Oil conversely had no influence. For the third aim, the chitosan coating was formed by dipping the products in a chitosan–lactic acid/Na-lactate solution from which the pH was adjusted to the pH of the products. These products were equilibrium modified atmosphere (EMA)-packaged, stored at 7°C and during storage sensorially and microbiologically evaluated. A chitosan coating on strawberries was applicable while on mixed lettuce the chitosan coating was not applicable due to the development of a bitter taste. The microbiological load on the chitosan-dipped samples was lower for both products. The antimicrobial effect of chitosan on lettuce disappeared after 4 days of storage, while it maintained on the strawberries during 12 days.

Antimicrobial Activity of Chitosan with Different Degrees of Acetylation and Molecular Weights

The antimicrobial activity of chitosan with different molecular weights (MWs) and different degrees of acetylation (DA) was examined to clarify how the activity depends upon the molecular structures. We determined minimum growth inhibitory concentrations (MICs) of various types of chitosan in L broth or its modified medium against bacteria and yeasts. The MICs against Gram-positive bacteria were relatively low for chitosan preparations with higher MWs and that against Gram-negative bacteria were at their minimum at around a MW of 11, 000 to 30, 000. An increase in the DA of the amino group in the chitosan molecule caused less activity. The antimicrobial activity varied with the genus as well as species of bacteria and yeasts. For application of chitosan as a preservative to food, pharmaceuticals, and other materials, the data obtained here on the characteristics and antimicrobial spectrum may be useful.

A new lipid emulsion formulation with high antimicrobial efficacy using chitosan

The antimicrobial activity of chitosan in lipid emulsions as well as in aqueous solutions was investigated. Two types of long-chained chitosan were used differing in the molecular weights, degree of the deacetylation and their viscosity: type I, mol. weight 8.7×10 4 g/mol, 92% degree of deacetylation and a viscosity of 14 mPa s, type II, mol. weight of 5.32×10 5 g/mol, 73% degree of deacetylation and a viscosity of 461 mPa s. In order to assess the pH optimum of the antimicrobial activity of the biopolymer, suspensions of the microorganisms Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans and Aspergillus niger were incubated at different pH-values in lactic acid solution (1% w/v) containing different concentrations of chitosan up to 1.5% (w/v). Emulsion formulations containing either 0.25%, 0.5% or no chitosan, respectively, were inoculated with the same microorganisms and were incubated at 25°C. The aqueous solutions as well as the emulsions were examined for microbial counts on agar plates after different periods of incubation. After 24 h of incubation in aqueous solutions only the cfu numbers of the bacteria were reduced. Both types of chitosan revealed a pH optimum of their antibacterial activity at pH 5.0–5.1 for P. aeruginosa, and at pH 5.3 for S. aureus. In addition, chitosan with a mol. weight of 8.7×10 4 g/mol, high degree of deacetylation and low viscosity showed a higher antimicrobial activity than the other chitosan type of this study. It was found that lipid emulsions containing 0.5% chitosan (type I) conformed to the requirements of the preservation efficacy test for topical formulations according to the European Pharmacopoeia while the emulsion without chitosan and a lactic acid solution with and without the biopolymer did not conform. In hemolysis studies on human erythrocytes, the hemolytic activity of the lipid emulsions with chitosan was assessed. These emulsions showed a negligible hemolytic behavior. The results indicate a use of chitosan as antimicrobial preservative in emulsion formulations for mucosal as well for parenteral applications.

Effects of steam sterilization on thermogelling chitosan-based gels.

A new thermogelling chitosan-glycerophosphate system has been recently proposed for biomedical applications such as drug and cell delivery. The objectives of this work were to characterize the effect of steam sterilization on the in vitro and in vivo end performances of the gel and to develop a filtration-based method to assess its sterility. Autoclaving 2% (w/v) chitosan solutions for as short as 10 min resulted in a 30% decrease in molecular weight, 3-5-fold decrease in dynamic viscosity, and substantial loss of mechanical properties of the resulting gel. However, sterilization did not impair the ability of the system to form a gel at 37 degrees C. The antimicrobial activity of chitosan against several microorganisms was evaluated after inoculation of chitosan solutions and removal of the cells by filtration. It was found that, although chitosan was bacteriostatic against the heat sterilization bioindicator Bacillus stearothermophilus, the bacteria could rapidly grow after separation from the chitosan solution by filtration. This indicated that B. stearothermophilus is an adequate strain to validate a heat sterilization method on chitosan preparations, and accordingly this strain was used to assess the sterility of chitosan solution following a 10 min autoclaving time.

Antimicrobial action of exogenous chitosan.

The objective of this chapter is to present fundamental factors (e.g. intrinsic and extrinsic) influencing chitosan as antimicrobial agent, for effective practical application. The antimicrobial activity of chitosan is well observed on a wide variety of micro-organisms including fungi, algae and some bacteria. However, the antimicrobial action is influenced by intrinsic and extrinsic factors such as the type of chitosan (e.g. plain or derivative); degree of chitosan polymerization; host natural nutrient constituency; substrate chemical and/or nutrient composition; and environmental conditions (e.g. substrate water activity (Aw) and/or moisture). Although both plain and derivative chitosans are effective as antimicrobial agents, there is a differential effect between them. Their differential antimicrobial effect is mainly exhibited in live host plants; thus the antifungal effect of N-carboxymethyl chitosan (NCMC) is different in vegetable as compared with graminea host. At the same time, pentamer and heptamer chitosan units seem to have better antifungal action than larger units. Chitosan antimicrobial action is more immediate on fungi and algae, followed by bacteria; the chitosan site of action is at the microbial cell wall.