title: Insights into the mode of action of chitosan as an antibacterial compound.
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, and 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, coupled to a significant membrane depolarization, was detected. 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 leads to multiple changes in the expression profiles of Staphylococcus 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.
authors.affiliation: Institute for Medical Microbiology, Immunology and Parasitology, Pharmaceutical Microbiology Unit, University of Bonn, Meckenheimer Allee 168, D-53115 Bonn, Germany. draafat@uni-bonn.de
authors.forename: Dina
authors.initials: D
authors.lastname: Raafat
authors.forename: Kristine
authors.initials: K
authors.lastname: von Bargen
authors.forename: Albert
authors.initials: A
authors.lastname: Haas
authors.forename: Hans-Georg
authors.initials: HG
authors.lastname: Sahl
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002462:Cell Membrane / Q000187:drug effects; D002473:Cell Wall / Q000187:drug effects; D048271:Chitosan / Q000494:pharmacology*; D015169:Colony Count, Microbial; D015870:Gene Expression / Q000187:drug effects; D020869:Gene Expression Profiling; D008564:Membrane Potentials / Q000187:drug effects; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability; D046529:Microscopy, Electron, Transmission; D010539:Permeability / Q000187:drug effects; D011188:Potassium / Q000378:metabolism; D013210:Staphylococcus / Q000187:drug effects* / Q000254:growth & development / Q000648:ultrastructure
chemical_list: D000900:Anti-Bacterial Agents; D048271:Chitosan; D011188:Potassium