As seen in Table 1, chitosans markedly inhibited growth of most bacteria tested; however, the inhibitory effects differed with regard to the molecular weight of chitosan and the type of bacterium. Chitosan generally showed stronger bactericidal effects for gram-positive bacteria than for gram-negative bacteria in the presence of 0.1% chitosan, as observed by Jeon et al. (2001). With gram-negative bacteria, chitosan of 746 kDa appeared most effective against E. coli and P. fluorescens, compared with chitosan (470 kDa) against S. typhimurium and V. parahaemolyticus. Chitosan of Mw=1106 and 224 kDa possessed weak or no antibacterial activity (Mw=28 kDa) against S. typhimurium. In contrast to the response of gram-negative bacteria, growth of gram-positive bacteria was almost or completely suppressed by widely different Mw chitosans.