Antibiofilm activity of shikimic acid against Staphylococcus aureus

The aim of this study was to evaluate the inhibitory activity of shikimic acid (SA) against biofilm formation of Staphylococcus aureus and to explore its potential molecular mechanism. Crystal violet staining assay showed that SA clearly reduced the biomass of the biofilm at its sub-MICs. Light microscopic images and scanning electron microscope (SEM) observations suggested that SA inhibited the biofilm adhesion on glass slides and induced apparent collapse of biofilm architecture. In addition, XTT reduction assay and confocal laser scanning microscopic images illustrated that the metabolic activity and the viability of the SA-treated biofilm cells significantly decreased. Cell mobility of the SA-treated S. aureus was also inhibited. These observations suggested that SA inhibited the initial biofilm formation by interfering the metabolic activity, the cell viability, and the cell mobility of S. aureus. However, SA failed to disrupt the one-day-old mature biofilm of S. aureus even at the concentrations higher than MIC, suggesting that SA disturbed the early steps in the biofilm formation of S. aureus. qRT-PCR analyses showed that SA down-regulated the transcription of sarA, while up-regulated the transcription of agrA, which resulted in the prevention of biofilm formation. So, SA could be a potential antibiofilm agent to inhibit biofilm formation of S. aureus.