Sensitization of Escherichia coli O157:H7 to Acidic Conditions by Chitosan and Nanochitosan

Chitosan, a natural nontoxic biopolymer derived by deacetylation of chitin, has received considerable attention for its commercial applications in the food industry. In the present study, the ability of chitosan and chitosan nanoparticles to sensitize Escherichia coli O157:H7 to low pH was assessed. To achieve this purpose, cells of E. coli O157:H7 were exposed to pH 4 and 5 adjusted by adding hydrochloric and acetic, acids into TSB, in the presence of 0.0, 0.05, 0.1 and 0.2 % chitosan, for one hour. Chitosan did not show antibacterial activity at pH 5, while 0.2 % nanochitosan made E. coli O157:H7 cells more sensitive to this pH. However, antibacterial activity of both chitosan and nanochitosan werehigher at pH 4, where 0.2 % chitosan and 0.1 and 0.2 % nanochitosan showed significant antibacterial effects on E. coli O157:H7 at this pH. In general, the higher antibacterial activity of nanochitosan than chitosan may be due to the nanoparticle's larger surface area and higher affinity with bacterial cells. Results of the fluorescent staining demonstrated that chitosan and nanochitosan exerted their effect by disrupting the cellular membrane of the cells.