Identification of essential oils with strong activity against stationary phase uropathogenic Escherichia coli

Escherichia coli is the most dominant pathogen causing urinary tract infections (UTIs), but the current most frequently prescribed antibiotics do not always effectively cure the infection due to quiescent persister bacteria, which present a treatment challenge because of frequent relapse. While it has been reported that some essential oils have antimicrobial activity against growing E. coli, the activity of essential oils against the non-growing stationary phase E. coli which is enriched in persisters has not been investigated. In this study, we evaluated the activity of 140 essential oils against stationary phase uropathogenic E. coli UTI89 and identified 39 essential oils at 0.5% concentration, 8 essential oils at 0.25% concentration, and 3 essential oils at 0.125% concentration to have high activity against stationary phase E. coli. Among the top eight essential oils, Oregano showed higher activity than the known persister drug tosufloxacin. The other top four hits including Allspice, Bandit thieves, Cinnamon bark, and Syzygium aromaticum could eradicate stationary phase E. coli at a low concentration of 0.25% after three- or five-day exposure, while Health shield, Cinnamon leaf, and Clove bud were found to be active at a higher concentration. In Oregano essential oil drug combination studies with common UTI antibiotics, Oregano plus quinolone drugs (tosufloxacin, levofloxacin, and ciprofloxacin) completely eradicated all stationary phase E. coli cells, partially enhanced the activity of nitrofurantoin, but had no apparent enhancement for fosfomycin, meropenem, and cefdinir. Our findings may facilitate the development of more effective treatments for persistent UTIs.