Abstract:Objective To investigate the inhibitory effect and mechanism of thymol on the biofilm formation of Proteus mirabilis (PM).Methods The minimal inhibitory concentration (MIC) and minimal biofilm inhibitory concentration (MBIC) of thymol were determined by the broth micro-dilution method. The time-kill curve of thymol was established by the colony counting method. Crystal violet staining was performed to determine the inhibitory effect of thymol on the biofilm formation of PM. The effects of thymol on the swarming and swimming of PM and the extracellular polymeric substances (extracellular polysaccharides, extracellular proteins, and eDNA) of the biofilm were determined. RT-qPCR was employed to investigate the effects of thymol on the expression levels of PM biofilm-related genes: rsbA (encoding histidine-containing phosphotransmitter of the bacterial two-component system), flhD (encoding the flagellar regulon), and mrpA (encoding mannose-resistant Proteus-like fimbriae).Results The MIC of thymol against PM was 0.156 mg/mL. Thymol significantly inhibited the biofilm formation of PM, with the MBIC of 0.313 mg/mL. Thymol inhibited the motility of PM, reduced the formation of extracellular polysaccharides, proteins, and eDNA in PM biofilm, and decreased the expression levels of rsbA, flhD, and mrpA.Conclusion Thymol inhibits the biofilm formation of PM by suppressing the motility and formation of extracellular polymers and down-regulating the expression of biofilm-related genes.