Comparative evaluation of antimicrobial activity of oligochitosans against Klebsiella pneumoniae

© 2015 Pleiades Publishing, Ltd. The Antibacterial activity of chitosan of different molecular weights was studied against gramnegative Klebsiella pneumoniae at different pH values. It was found that the dependence of the inhibitory activity of chitosan on its molecular weight was undergoes inversion when increasing the pH of the medium above 7.0. In acidic media, chitosan of the higher molecular weight had the higher antibacterial activity, while in weàk alkaline media, oligomeric forms of chitosan displayed only the inhibition effect. Our results showed that the antibacterial activity of chitosan against Klebsiella pneumoniae was closely associated with its polycationic nature, and depended on the degree of protonation of the chitosan amino groups, which, in turn was the function of the degree of polymerization and the pH values of the medium. The results allow one to explain, in part, the contradictory literature data concerning the relationship between the antibacterial activity and molecular weight of chitosan

N-Reacetylated Oligochitosan: pH Dependence of Self-Assembly Properties and Antibacterial Activity

© 2017 American Chemical Society.Oligochitosan (short chain chitosan) is more soluble in acidic aqueous media than a high molecular weight (MW) chitosan, but its antimicrobial activity decreases with increase in degree of acetylation (DA) and increase in pH above a critical pH threshold point. In the present study, oligochitosans varying in MW were additionally N-acetylated and their self-assembly properties and antibacterial activity toward Staphylococcus aureus and Escherichia coli were investigated in a wide pH range as a function of MW and DA. Light scattering studies reveals that reacetyleted oligochitosan with Mw ≤ 11 kDa is completely soluble in alkaline media (up to pH 12.5), if its DA is not less than 16%. Reacetylated chitosans with DA ∼ 30% are solubile in the entire pH range up to 12.5, if their Mw is not higher than 25 kDa, but they aggregate and precipitate from the solution at pH ≥ 8 when their Mw is above 25 kDa. Considering the influence of DA and MW, the antibacterial activity of reacetylated oligochitosans is maximal in the short interval of DA 16-28% at pH 7.4. These results are promising for expanding practical application of oligochitosan in pharmaceutical, cosmetic, and food compositions

Antifungal activity of oligochitosans (short chain chitosans) against some Candida species and clinical isolates of Candida albicans: Molecular weight-activity relationship

A series of oligochitosans (short chain chitosans) prepared by acidic hydrolysis of chitosan and characterized by their molecular weight, polydispersity and degree of deacetylation were used to determine their anticandidal activities. This study has demonstrated that oligochitosans show a high fungistatic activity (MIC 8-512 μg/ml) against Candida species and clinical isolates of Candida albicans, which are resistant to a series of classic antibiotics. Flow cytometry analysis showed that oligochitosan possessed a high fungicidal activity as well. For the first time it was shown that even sub-MIC oligochitosan concentration suppressed the formation of C. albicans hyphal structures, cause severe cell wall alterations, and altered internal cell structure. These results indicate that oligochitosan should be considered as a possible alternative/additive to known anti-yeast agents in pharmaceutical compositions. © 2014 Elsevier Masson SAS. All rights reserved

Molecular weight and pH aspects of the efficacy of oligochitosan against methicillin-resistant Staphylococcus aureus (MRSA)

Oligochitosan samples varying in molecular weight (Mw) and having narrow polydispersities were prepared by means of depolymerization of chitosan in hydrochloric acid, and their antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) was measured at pH values 5.5-8.0. The antibacterial testing of oligochitosans obtained showed that oligochitosans having Mw in the range of 0.73-20.0 kDa could be used both at slightly acidic and neutral pH values, and that the activity against MRSA remained moderate for oligochitosan samples having Mw about 3-5 kDa even at slightly basic pH values. The self-assembling behavior of oligochitosan macromolecules in the dilute solution at various pH values as a function of chain length was investigated. At first it was shown that oligochitosans formed supramolecular aggregates in dilute solutions below the critical pH value 6.5. Despite the aggregation phenomenon, the formation of nano-sized aggregates did not prevent oligochitosan from demonstrating the bactiostatic activity. © 2011 Elsevier Ltd. All Rights Reserved

Evaluation of a method for the determination of antibacterial activity of chitosan

© 2016, Pleiades Publishing, Inc.A method for the determination of the antimicrobial activity of chitosan with the use of organic salts for the production of pH in the range of 5.5–8.2 was studied. The double-dilution method demonstrated the effectiveness of the determination of the antimicrobial activity of chitosan samples with different molecular weights and solubilities. It was found that the antibacterial activity increased at low pH values with increasing molecular weight, but chitosans with a molecular weight of 5–6 kDa showed higher activity at neutral and slightly alkaline pH levels. Determination of the antimicrobial activity of various chitosan samples at different pH values allowed a more reliable assessment of the potential biological activity of chitosan

Effect of Molecular Weight and Degree of Acetylation on Adjuvantive Properties of Chitosan Derivatives

© 2018, Pleiades Publishing, Inc. The hemostatic and immunostimulating activity and cytotoxicity were determined for a number of chitosans differing in molecular weight (from 3 to 510 kDa) and degree of acetylation (from 1 to 25 mol%) that were used as adjuvants in inactivated poliomyelitic, influenza, and live influenza vaccines. It has been shown that the hemostatic activity of chitosan increased sharply with an increase in its molecular weight. In oligochitosan with a molecular weight of <16 kDa, it was smaller by a factor of 15–100 than in chitosan with a molecular weight of 20–510 kDa. The level of increase in the immunogenicity of vaccines containing oligochitosan as adjuvants was not lower than that for the vaccine including high-molecular chitosan. However, the immunostimulatory activity of oligochitosan depended on the degree of acetylation, reaching a maximum value at 6 mol%. It was shown that all oligochitosans and chitosans with a molecular mass below ~50 kDa showed almost no cytotoxicity at a concentration of ≤2.5 mg/mL, which enable their use as adjuvants for inactivated and live vaccines at the optimal ratio of molecular weight to the degree of acetylation

Comparative evaluation of antimicrobial activity of oligochitosans against Klebsiella pneumoniae

© 2015 Pleiades Publishing, Ltd. The Antibacterial activity of chitosan of different molecular weights was studied against gramnegative Klebsiella pneumoniae at different pH values. It was found that the dependence of the inhibitory activity of chitosan on its molecular weight was undergoes inversion when increasing the pH of the medium above 7.0. In acidic media, chitosan of the higher molecular weight had the higher antibacterial activity, while in weàk alkaline media, oligomeric forms of chitosan displayed only the inhibition effect. Our results showed that the antibacterial activity of chitosan against Klebsiella pneumoniae was closely associated with its polycationic nature, and depended on the degree of protonation of the chitosan amino groups, which, in turn was the function of the degree of polymerization and the pH values of the medium. The results allow one to explain, in part, the contradictory literature data concerning the relationship between the antibacterial activity and molecular weight of chitosan