Chitosan as an antibacterial compound: Insights into its mode of action

Institute for Medical Microbiology, Immunology and Parasitology (IMMIP) – Pharmaceutical Microbiology Unit - University of Bonn, D-53115 Bonn, Germany; Institute for Cell Biology - University of Bonn, D-53121 Bonn, Germany

^* To whom correspondence should be addressed. Email: draafat{at}uni-bonn.de.

	Abstract

Chitosan is a polysaccharide biopolymer that combines a unique set of versatile physicochemical and biological characteristics, which allow for a wide range of applications. Although its antimicrobial activity is well-documented, its mode of action has hitherto remained only vaguely defined.

In this work we investigated the antimicrobial mode of action of chitosan using a combination of approaches, including in vitro assays, killing kinetics, cellular leakage measurements, membrane potential estimations, electron microscopy, in addition to transcriptional response analysis.

Chitosan, whose antimicrobial activity was influenced by several factors, exhibited a dose-dependent growth-inhibitory effect. A simultaneous permeabilization of the cell membrane to small cellular components was detected, coupled with a significant membrane depolarization. A concomitant interference with cell wall biosynthesis was not observed. Chitosan treatment of Staphylococcus simulans 22 cells did not give rise to cell wall lysis; the cell membrane also remained intact. Analysis of transcriptional response data revealed that chitosan treatment lead to multiple changes in the expression profile of S. aureus SG511 genes involved in the regulation of stress and autolysis, as well as genes associated with energy metabolism. Finally, a possible mechanism for chitosan's activity is postulated. Although we contend that there might not be a single classical target that would explain chitosan's antimicrobial action, we speculate that binding of chitosan to teichoic acids, coupled with a potential extraction of membrane lipids (predominantly lipoteichoic acid) results in a sequence of events, ultimately leading to bacterial death.