Antimicrobial activity of Ag+, Cu2+, Zn2+, Mg2+ ions doped chitosan nanoparticles

Abstract

Modification by polymers and inorganic ions of the bioactive materials for orthopedic implants with the purpose of initiating controlled reactions in tissues that surround the implant, is one of the modern approaches in medical materials.  A key feature of functional polymers is their ability to form complexes with various metal ions in solution. Chitosan is natural biopolymer with pronounced affinity to transition metal ions. Some researches prove the higher antimicrobial activity of Chitosan-metal complexes compared with pure Chitosan. The purpose of this work was the study of antimicrobial activity of Chitosan nanoparticles modified by metal ions Ag+, Cu2+, Zn2+, Mg2+ against reference strains S. aureus 25923 ATSS, E. coli ATCC 25922, C. albicans ATCC 885653 for their further use as components of the composite biomaterials for medical purpose. Chitosan nanoparticles suspension was prepared by known method based on the ionotropic gelation between chitosan and sodium tripolyphosphate. To obtain Chitosan-metal nanoparticles to the Chitosan suspension were added the corresponding metal ions aqueous solutions in quantity to match the concentration of metal ions of 200 ppm .  Antibacterial activities of Ag+, Cu2+, Zn2+, Mg2+ ions doped Chitosan nanoparticles, pure Chitosan nanoparticles, metal ions and 1% (v/v) acetic acid solution (it was used as solvent for Chitosan) against bacteria were evaluated by determination of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) in vitro. Muller–Hinton (MH) broth and MH agar (Russia) were used as growth media. The bacteria suspension for further use was prepared with concentration that corresponded 0,5units by McFarland scale. The MIC was determined by a broth dilution method. The results were read after 24 hours of experimental tubes incubation at 37 oC as equivalent to the concentration of the tube without visible growth. To evaluate MBC, a sample of 0,1 ml was transferred from each tube without visible growth to a MH agar plate and incubated at 37 oC for another 24 hours. The MBC was determined as the concentration of the tube without bacterial growth. Results showed that antibacterial activity of the ion metal loaded Chitosan nanoparticles was higher than that of pure Chitosan nanoparticles and significantly higher than antibacterial activity of the metal ions. The acetic acid MIC was highest and there is the evidence of the nanoparticles antibacterial action, but not of the solvent.  The most sensitive to all investigated samples was gram-negative microorganism Е. coli ATCC 25922, the most stabile – funge C. albicans ATCC 885653. So, for example, Silver nanoparticles compared with pure Chitosan nanoparticle were at 8, 4, 2 times more active against Е. coli, S. аureus, C. albicans respectively, as compared with the Ag+ ion antibacterial activity – at 5, 40 and 10 times respectively. Adding copper ions Cu2+ to Chitosan nanoparticles increased their antimicrobial action against S.aureus compared with pure Chitosan nanoparticles in 4 times, but it does not affect antimicrobial activity against the other two of the microorganisms. Addition of zinc (Zn2+) and magnesium (Mg2+) ions increased antimicrobial activity against E. coli in 2 times. The results of this study suggest about the perspective of Ag+, Cu2+, Zn2+ ions doped Chitosan nanoparticles applications as the antimicrobial component to composite materials for medical purpose.