Antimicrobial Activity And Mechanism Of Chitosan And Its Combinations With Surfactants

Chitosan, a copolymer consisting of ? (1,4)- 2- acetamido - 2 - deoxy- D- glucose and 0-(1,4) -2- amino -2- deoxy -D-glucose units, has attracted considerable interests due to its biological activities such as antimicrobial, antitumor, immune enhancing effects, and its nontoxicity, degradability, renewability. As antimicrobial agent, chitosan and its derivatives can inhibit the growth of many bacteria and fungi. At present, studies about antimicrobial activity of chitosan and its derivates, factors, the tructure-activity relationship and its mechanism are not clear. The resent progresses on the antimicrobial activity of chitosan and its derivatives, its factors, mechanism and application were summarized in this paper. The effects of structure on the antimicrobial activity of chitosan and its derivatives, as well as the mechanism of antimicrobial activity, were systematically studied. And the antimicrobial and surface activity of chitosan combined with surfactants, as well as the interactions between chitosan and surfactant molecule, were also studied, so as to determine compatibility-structure-antimicrobial activity relationship, and find out the mechanism and regularity of the improved antimicrobial activity of chitosan by surfactants.The main contents and conclusions are summarized as below:1. Ultrasonic degradation of chitosan: 28 chitosan samples with different Mw (98.3 ?104-91? 104) and DD (92-55%) were prepared by ultrasonic degradation of 4 raw chitosan materials (Mw: 154 ?104-44.7 ?104, DD: 91.6-61.9%), and their Mw, DD, crytallinities were characterized by GPC, UV, IR, XRD. It showed that chitosan with higher Mw and lower DD showed faster degradation; The Mw polydispersity of treated chitosans were narrower, the higher the Mw of raw chitosan, the narrower the polydispersity of the degraded samples; The crystallinity of ultrasonic treated chitosan was higher; Ultrasonic treatment decreased the DD of chitosan, especially the DD of chitosan with higher Mw (154 ?04) and lower DD (72.1%) decreased to 55.1%.2. Antimicrobial activity of chitosan and its derivatives: The minimum inhibition concentration (MIC), inhibition time (IT), inhibition rate and biocidal effect (within 180 min) of chitosan and its derivatives, against gram-positive bacteria such as 5. aureus, S. epidermidis, gram-negative bacteria such as E. coli, P. aeruginosan, fungi C. albicans, were determined using Agar plate and liquid medium methods. ?0.5% chitosan killed 1.2 log CFU/ml E. coli in 5 min, all E. coli and some Staphylococcus aureus in 120 min , and inhibited the growth of E. coli, Pseudomonas aeruginosa, S.aureus, Staphlococcus epidermidis, but not Candida albicans. Minimum inhibition concentrations (MICs) against bacteria were in the range of 0.025~0.05%; ?the antimicrobial activity of chitosan samples gained from enzyme hydrolysis decreased with decreasing Mw, especially that with Mw lower than 10000, whose MICs could be 1 times lower; (3) the antimicrobial activity of chitosan treated by ultrasonic, with low Mw and high DD, showed strongest inhibition effect; antimicrobial activity of chitosan with similar DD increased with decreasing Mw; but the antimicrobial activity of chitosan with similar Mw was not bound to increase with increasing DD, which was related to the molecular structure of samples; ?through analyzing the antimicrobial activity of chitosan derivatives, it is considered that the amino group of chitosan is critical to its antimicrobial activity, and the modification that increases the positive charge of chitosan molecule or benefits to the interaction between chitosan and negative charged bacterial surface will improve antimicrobial activity, or the case is converse. (5) The antimicrobial activity of chitosan acetate solution combined with other organic acids such as benzole acid, salicylic acid, ascorbic acid and citric acid solutions exhibited longer inhibition time than chitosan acetate solution alone. And the mixed solution of 0.05% chitosan acetate and 0.01% salicylic acid solution showed the best antim...