In the case of S. aureus and S. epidermidis, chitosans showed a stronger antibacterial activity than COS. Apparently, chitosan exhibits a stronger bactericidal effect upon Grampositive than -negative bacteria [20]. The MICs varied from 0.10% (for both bacteria, in the case of high and medium MW) to 0.25% (w/v) (for both COS), or 0.20%
regarding S. epidermidis. Our results suggested higher MICs than those reported by Jeon et al. [12]: 0.06% (w/v) of 685 kDa chitosan was required to inhibit either S. aureus or S. epidermidis growth, as well as ca. 0.12% (w/v) of COS (ca. 5 kDa) to inhibit S. aureus, and 0.25% (w/v) thereof to inhibit S. epidermidis. This observation may be explained by the higher deacetylation degree of chitosans/COS used by those authors (89%), which implies a higher number of side amine groups available for reaction;
note that this rationale has been proposed by several authors as responsible for chitosans antibacterial action [23, 38, 39].