Influence of cyclopropane fatty acids on heat, high pressure, acid and oxidative resistance in Escherichia coli

Heat and high pressure resistant strains of Escherichia coli are a challenge to food safety. This study investigated effects of cyclopropane fatty acids (CFAs) on stress tolerance in the heat- and pressure-resistant strain E. coli AW1.7 and the sensitive strain E. coli MG1655. The role of CFAs was explored by disruption of cfa coding for CFA synthase with an in-frame, unmarked deletion method. Both wild-type strains consumed all the unsaturated fatty acids (C-16:1 and C-18:1) that were mostly converted to CFAs and a low proportion to saturated fatty acid (C16;0). Moreover, E. coli AW1.7 contained a higher proportion of membrane C-19:0 cyclopropane fatty acid than E. coli MG1655 (P < 0.05). The Delta cfa mutant strains did not produce CFAs, and the corresponding substrates C16:1 and C18:1 accumulated in membrane lipids. The deletion of cfa did not alter resistance to H2O2 but increased the lethality of heat, high pressure and acid treatments in E. coli AW1.7, and E. coli MG1655. E. coli AW1.7 and its Delta cfa mutant were more resistant to pressure and heat but less resistant to acid stress than E. colt MG1655. Heat resistance of wild-type strains and their cfa mutant was also assessed in beef patties grilled to an internal temperature of 71 degrees C. After treatment, cell counts of wild type strains were higher than those of the Delta cfa mutant strains. In conclusion, CFA synthesis in E. coli increases heat, high pressure and acid resistance, and increases heat resistance in food. This knowledge on mechanisms of stress resistance will facilitate the design of intervention methods for improved pathogen control in food production. (C) 2016 Elsevier B.V. All rights reserved.