Activity of chitosan films against different microorganisms

Chitosan is a hydrophilic polysaccharide which derives from chitin by deacetylation. It has several applications, namely as a film that can be applied to preserve the quality and increase the shelf-life of food. Chitosan is insoluble in most solvents but it is soluble in dilute organic acids such as formic acid and acetic acid[1]. The properties of chitosan depend on the degree of deacetylation (DA) and molecular weight (MW). A broad antimicrobial activity has been attributed to chitosan, either for gram-negative, gram-positive bacteria and fungi. The aim of the present study is to evaluate the antimicrobial activity of a chitosan film prepared by casting. The chitosan was obtained from shrimp waste collected from shrimp processing factories of South Sonora (Mexico). Four bacteria (Bacillus cereus; Escherichia coli; Staphylococcus aureus and Listeria monocytogenes) and one fungus (Botrytis cinerea) were evaluated. Although L. monocytogenes and B. cinerea growth was not inhibited by the chitosan film, results showed a clear growth-inhibitory effect, at the two bacteria concentration levels tested, for B. Cereus, E. coli and S. aureus. Different antibacterial mechanisms have been proposed to explain chitosan antimicrobial activity[2-3]: i) chitosan may form an external barrier which inhibits essential nutrients adsorption; ii) chitosan can also penetrate the microbial cell, disturbing the metabolism of the cell by inhibiting the mRNA and protein synthesis; iii) chitosan may have an ionic surface interaction with the bacteria originating wall cell leakage. Although these mechanisms may take place simultaneously, the antimicrobial activity may also depend on the properties of chitosan (DA and MW).This work was carried out under the Project no. 95935 from FONCICYT C002-2008-1/ ALA – 127 249, with the financial support of the European Union and CONACYT. The authors are grateful to the postdoctoral contract of Ana Sanches Silva in the frame of the Program ‘‘Science 2007’’ funded by “Fundação para a Ciência e a Tecnologia’’, Portugal