Thymol : inhibitory activity on Escherichia coli and Staphylococcus aureus adhesion to human vaginal cells

Adhesion is an important starting event in the pathogenesis of bacterial infection because the microorganisms must first adhere to host tissue in order to multiply and create a colony or colonies before specific symptoms allow the disease process to be detected. This is particularly true in the case of female urogenital infections, including urinary tract infections, bacterial vaginosis and vaginitis. Thymol is a component of thyme essential oil, which has been reported to possess interesting antimicrobial effects on various microorganisms; however, its ability to interact with the adhesion of bacteria (an important determinant of bacterial virulence) has not been investigated. The aim of this study was to assess whether thymol interferes with the adhesion of Escherichia coli and Staphylococcus aureus to human vaginal epithelial cells. The adhesiveness of three strains of E. coli to vaginal cells was significantly reduced at thymol concentrations ranging from 1/2 MIC to 1/32 MIC, and in three strains of S. aureus at concentrations ranging from 1/2 MIC to 1/16 MIC. Sub-MICs down to 1/8 MIC also significantly reduced the hemagglutination of E. coli, which is correlated with fimbriation and thus provides a clue relating to the interference of thymol, a phenolic structure with an hydroxyl group, on the physico-chemical characteristics of the outer surface of bacteria. This is of interest for the strategy of protecting against vaginitis or vaginosis using drugs other than antibiotics.