Differential Susceptibility of <i>Escherichia coli</i> O157:H7 and Non-O157 Strains to Water-Soluble Chitosan and Its Application in Controlling <i>E. coli</i> Contamination on Lettuce

Abstract Purpose This study compared the antimicrobial susceptibility of Escherichia coli O157:H7 and non-O157 strains to water-soluble chitosan (WSC) to assess strategies for reducing the risks posed by non-O157 strains in food systems. Methods The minimum inhibitory concentration (MIC) of WSC against E. coli strains was determined using an agar diffusion assay. The sensitivities of both strain groups to WSC and the effect of WSC on their growth were evaluated at various concentrations. For the food application study, romaine lettuce inoculated with E. coli O157:H7 and a non-O157 strain was treated with WSC and stored at 4 °C for seven days. Results Differential susceptibility to WSC was observed between E. coli O157:H7 and non-O157 strains. The inhibitory effect of WSC was bactericidal or bacteriostatic depending on its concentration and treatment time. Strains O45:H2 and O145:NH showed higher resistance to WSC compared to O157:H7 strains. In romaine lettuce, WSC-induced cellular injury was less pronounced in E. coli O145:NH than in E. coli O157:H7 F12. Conclusion Non-O157 E. coli strains exhibited lower susceptibility to WSC than O157:H7 strains, both in laboratory media and in lettuce, indicating that WSC alone may not be sufficient to control these strains and highlighting the potential food safety risks if used as a sole control measure.