Evaluation of the Lemon Juice Induced Changes in Fatty Acid Composition, Membrane Fluidity and Virulence in Pathogenic Escherichia coli

Acidification is a crucial preservation technique that affects the survival and infection of foodborne pathogens. In this study, influence of the acidic growth medium on the resistance pattern of the pathogenic Escherichia coli in terms of changes in fatty acid composition as well as expression of virulent genes (eae, stx1, stx2 and hlyA) was investigated. It was revealed that lemon juice mediated acidic pH induced the transcription of stx2, with 3.1- and 2.5-fold increase of survived cells at pH 3.5 and 4.5, respectively, while the transcription level of stx1 in cells grown at pH 3.5 and 4.5 were 0.57 and 0.71-fold lower compared to control. Highest transcription level was observed in the cells grown at pH 3.5 and containing hlyA (4.6-fold), which was much higher than that at pH 5.5 and 4.5. However, pH had no effect on the transcription of eae gene. The results showed that isolated pathogenic E. coli cells from meat were susceptible to lemon juice mediated stress possibly due to the increased level of unsaturated fatty acid (USFA) and decreased level cyclic fatty acid (CFA). The fluidity of the membranes increased as the pH of the media dropped. The highest USFA/SFA ratio was observed in strains incubated at pH 3.5 with ratio of 0.31-0.38 and the value decreased as the pH increased, reaching a minimum value of 0.03 at pH 7.0. This study emphasizes on the importance of establishing effective strategies to combat acid-resistant pathogenic E. coli in food matrices.