2003 Volume 8 Issue 1 Pages 25-30
The antimicrobial activity of chitosan with different molecular weights (MWs) and different degrees of acetylation (DA) was examined to clarify how the activity depends upon the molecular structures. We determined minimum growth inhibitory concentrations (MICs) of various types of chitosan in L broth or its modified medium against bacteria and yeasts. The MICs against Gram-positive bacteria were relatively low for chitosan preparations with higher MWs and that against Gram-negative bacteria were at their minimum at around a MW of 11, 000 to 30, 000. An increase in the DA of the amino group in the chitosan molecule caused less activity. The antimicrobial activity varied with the genus as well as species of bacteria and yeasts. For application of chitosan as a preservative to food, pharmaceuticals, and other materials, the data obtained here on the characteristics and antimicrobial spectrum may be useful.