Carvacrol-rich oregano oil and thymol-rich thyme red oil inhibit biofilm formation and the virulence of uropathogenic Escherichia coli

Aims: Urinary tract infections are caused primarily by uropathogenic Escherichia coli (UPEC), and indwelling catheters are usually colonized by UPEC biofilms tolerant to common antibiotics. Hence, UPEC biofilms pose a substantial challenge, and there is an urgent need for effective control strategies. Methods and Results: In this study, 79 essential oils were screened for antibiofilm ability against UPEC. Components of active oils were identified, and their antibiofilm activities were also investigated using 96-well plates with crystal violet assay, scanning electron microscopy, and confocal laser scanning microscopy. Oregano oil and thyme red oil and their major common constituents, carvacrol and thymol, significantly inhibited UPEC biofilm formation at subinhibitory concentrations (<0.01%). These findings were supported by observations that carvacrol and thymol reduced fimbriae production and the swarming motility of UPEC. Furthermore, carvacrol and thymol markedly decreased the hemagglutinating ability of UPEC, and UPEC was more easily killed by human whole blood in the presence of carvacrol and thymol. Conclusions: Carvacrol-rich oregano oil and thymol-rich thyme red oil have high antibiofilm and antivirulence activities against UPEC. Significance and Impact of Study: In the wake of rising antimicrobial resistance, we envisage that carvacrol and thymol could be used to prevent biofilm formation by UPEC and to reduce its virulence.