Insight into the effect of quinic acid on biofilm formed by Staphylococcus aureus

Abstract

The biofilm formation of Staphylococcus aureus on food contact surfaces is the main risk of food contamination. In the present study, we firstly investigated the inhibitory effect of quinic acid (QA) on biofilm formed by S. aureus. Crystal violet staining assay and microscopy analysis clearly showed that QA at sub-MIC concentrations was able to significantly reduce the biofilm biomass and cause a collapse on biofilm architecture. Meanwhile, fibrinogen binding assay showed that QA had obviously effect on the S. aureus bacteria adhesion. XTT reduction assay and confocal laser scanning microscopic images revealed that QA significantly decreased metabolic activity and viability of biofilm cells. In addition, qRT-PCR analysis explored the potential inhibitory mechanism of QA against biofilm formation, which indicated that QA significantly repressed the gene sarA and activated the gene agrA. Moreover, QA exhibited a highly ability to reduce the number of sessile S. aureus cells adhered on the stainless steel. So, it was suggested that QA could be used as a promising antibiofilm agent to control biofilm formation of S. aureus.

Fig. 1. Effect of quinic acid on the planktonic growth and biofilm biomass of S. aureus ATCC 29213. Data were expressed as mean ± standard deviation (n = 3). **P < 0.01, compared with control.

Fig. 2. Microscopic visualization of inhibitory activity of quinic acid against S. aureus ATCC 29213 biofilm formation by scanning electron micrographs at 2000 and 5000 times magnification, respectively.

Fig. 3. Effect of quinic acid on the relative percentage adhesion of S. aureus ATCC 29213 to fibrinogen. Data were expressed as mean ± standard deviation (n = 3). **P < 0.01, compared with control.

Fig. 4. Effect of quinic acid on the metabolic activity of S. aureus ATCC 29213 biofilm cells (A). Data were expressed as mean ± standard deviation (n = 3). *P < 0.05, **P < 0.01, compared with control. The confocal laser scanning microscopic images at 620 times magnification of S. aureus ATCC 29213 biofilm stained with LIVE/DEAD BacLight bacterial viability kit for untreated cells (B) and treatment with 1.25 mg mL⁻¹ of quinic acid (C).

Fig. 5. qRT-PCR results of five related genes (icaR, icaA, sigB, agrA, sarA) in S. aureus ATCC 29213 biofilm formation with 1.25 mg mL⁻¹ of quinic acid treatment (A). Data were expressed as mean ± standard deviation (n = 3). *P < 0.05, **P < 0.01, compared with control. A proposed model for regulatory pathway of S. aureus ATCC 29213 biofilm formation in the presence of quinic acid (B).

Fig. 6. Effect of quinic acid on the population of S. aureus ATCC 29213 biofilm cells adhered to stainless steel. Data were expressed as mean ± standard deviation (n = 3). **P < 0.01, compared with control.