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 .
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.
Hong Li,Haiying Cui,Tariq Aziz,Ashwag Shami,Abdelrahman R. Ahmed,Fakhria A. Al-Joufi,Lin Lin
Inhibitory mechanism of phloretin on the AgrA LytTR- agr complex was revealed. • The AgrA LytTR domain protein was purified successfully. • EMSA confirmed phloretin may disrupt the binding of AgrA LytTR domain and P3 promoter. • MD simulations revealed that phloretin sterically hindered AgrA- agr binding, validated by mixed fluorescence quenching. • Phloretin acts as QSI to inhibit the secretion of enterotoxin and hemolysin in beef. Staphylococcus aureus ( S. aureus ) represents a major foodborne pathogen whose enterotoxin production poses significant challenges to food safety due to its high environmental resistance and limited efficacy of conventional sterilization. Since the expression of enterotoxins is predominantly governed by the agr quorum sensing system, targeting this regulatory pathway has become a strategic choice for virulence control. This study elucidated the mechanism by which phloretin, a potential quorum sensing inhibitor, interferes with the agr system to attenuate virulence. To achieve this, the recombinant AgrA LytTR domain was expressed and purified, and its interaction with phloretin was characterized using thermal shift assays (TSA), electrophoretic mobility shift assays (EMSA), and molecular dynamics (MD) simulations. The results showed that phloretin specifically binds to the AgrA LytTR domain, enhancing its thermal stability and disrupting AgrA LytTR- agr operon binding by reducing the free energy of interaction between them, without causing significant structural rearrangement. Mechanistic analysis indicated that phloretin sterically hinders key β -sheet turn residues (HIS169, ASN201, ARG233), thereby impairing DNA recognition, downregulating RNAIII transcription, and inhibiting agr signaling. In cooked beef, phloretin significantly inhibited the secretion of enterotoxins and α -hemolysin, while delaying lipid oxidation and protein degradation, and maintaining the meat texture. These findings suggested that phloretin is a multifunctional substance with anti-virulence, antioxidant, and preservative properties, demonstrating its potential as a natural food preservative. Download: Download high-res image (118KB) Download: Download full-size image
危险品化学品经营许可证（带存储）