1. Antibacterial Effect of Chitosan Flake Suspension in Water Yves ANDRES, Laurence GIRAUD and Pierre Le CLOIREC Ecole des Mines de Nantes, GEPEA, UMR CNRS 6144 4 rue Alfred Kastler, BP 20722, 44307 Nantes cedex 03 France e-mail: yves.andres@emn.fr Chitosan, the deacetylated derivative of chitin, is a natural D-glucosamine polymer that can be extracted from the shells of seafood such as prawns crabs and lobsters. Chitosan has free amino groups, which can interact with metal ions from solutions. It can be used as a flocculent, thickener, chromatography column matrix, gas-selective membrane, plant disease resistant promoter, anti-cancer agent, wound healing promotion agent and antimicrobial agent. The aim of this poster is to study of the interaction between chitin or chitosan flakes and various kinds of pathogen microorganisms potentially present in water in order to show the antimicrobial effects of those materials. The ideal structure of chitosan is a linear polysaccharide of b-(1,4)-2-amino-2-deoxy-D-glucopyranose (Figure 1a) where at least 50 % of residues are N- glucosamine, the others could be acetylated. This compound is the principal derivative of chitin (Figure 1b) which is the fully acetylated form. Introduction & Objectives Results & Discussion Conclusions The antimicrobial effect of chitosan onto Gram positive and negative bacteria depends on the deacetylation level and the chitosan concentration. The antimicrobial activity seems to be in relation with a polyelectrolytic effect confirmed by the potassium release. Reuse of chitosan is shown. Figure 1: Chemical structural representation of chitosan (a) and chitin (b). Figure 2: Survival curves of Escherichia coli (CIP 54.8 = ATCC 11775) (  ), Pseudomonas aeruginosa (CIP A 22) (  ), Enterococcus faecalis (CIP 76.117) (  ) and Staphylococcus saprophyticus (CIP 76.125) (  ) in NaCl : (A) in demineralized water pH 6.5 ± 0.3. (B) in demineralized water with 0.75 g/L of chitosan (80%) flakes at pH 6.5 ± 0.3. Table1: Mortality rate constant (min –1 ) for bacteria in four experimental condition: deionised water, suspension with chitosan at 80 % and 60 % of deacetylation, and with chitin. B A Table 1 collects the values for the mortality constant rate calculated from survival curves (Figure 2A and 2B). The curves show an exponential decrease and a mortality rate constant (k) could be calculated: From the first set of experimental data, only with sterile deionised water, a survival sequence is extrapolated: SS < PA < EC < EF. In the case of chitin flakes EC and PA present a growth rate explaining the negative values of the constant. It could be note that chitin have a protection effect. Moreover, chitosan (80 %) exhibits great mortality rate constant with the following order: EC < EF < SS < PA. Finally, the deacetylation level have an influence on the anti-microbial activity. Effectively, if we compare the results of the 60 %, the 80 % deacetylated chitosan and the chitin are compared we can notice an increase of the constant in relation to the deacetylation level. These results clearly show that chitosan have a significant effect on bacteria survival.