Effect of sublethal thymol, carvacrol and trans-cinnamaldehyde adaptation on virulence properties of Escherichia coli O157:H7

Essential oils (EOs) have demonstrated wide-spectrum antimicrobial activities, and have been actively studied for their application in foods as alternative natural preservatives. However, information regarding microbial adaptive responses and changes in virulence properties following sublethal EO exposure is still scarce. The present study investigated the effect of sublethal thymol (Thy), carvacrol (Car) or trans -cinnamaldehyde (TC) adaptation on virulence gene expression and virulence properties of Escherichia coli O157:H7. Results demonstrated that E. coli O157:H7 grown to early stationary phase in the presence of sublethal EO showed significantly ( P E. coli O157:H7, which could benefit to their application in the food industry. IMPORTANCE The present study was conducted to evaluate changes in virulence properties in Escherichia coli O157:H7 adapted to sublethal essential oils (EOs). Results demonstrated reduced motility, biofilm-forming ability and efflux pump activities in EO-adapted E. coli O157:H7, with no induction of antibiotic resistance nor infection (adhesion and invasion) on Caco-2 cells. RT-qPCR results revealed changes in the expression of related virulence genes. Thus, the present study provides new insights into microbial virulence behavior following EO adaptation, and suggests that Thy, Car and TC sublethal exposure did not constitute a significant risk in inducing microbial virulence.