Transcriptomic Analysis of the Effect of Glabridin on Biofilm Formation in Staphylococcus Aureus

Staphylococcus aureus (S. aureus) is among the major skin infection-causing pathogens in animals and humans. Its ability to form biofilms has become a foremost cause of bacterial infections and the extensive spread of drug resistance, which poses a great difficulty in clinical treatment. Glabridin (Glb), an extract of licorice with antibacterial and anti-infective properties, has a partially understood biofilm-inhibitory mechanism. This study investigated the inhibitory and antibiofilm activities of subinhibitory concentrations of Glb against S. aureus. The crystal violet assay revealed that Glb significantly suppressed biofilm expression. Scanning electron microscopy observations unveiled that Glb reduced S. aureus adhesion and accumulation by disrupting the spatial structure of the biofilm. In vitro extracellular DNA (eDNA) inhibition assays demonstrated that Glb inhibited biofilm formation by S. aureus by suppressing eDNA secretion. In total, 184 differentially expressed genes were obtained through transcriptomic (RNA-seq) sequencing, of which 81 and 103 genes were upregulated and downregulated, respectively. Glb regulated the transcript levels of biofilm-related genes through the phosphatase transfer system, two-component regulatory system, and nitrogen metabolism. The qPCR analysis was performed to confirm whether Glb interfered with the expression of regulatory genes involved in S. aureus biofilm formation (SarA, ArlR, FnbA, ClfA, icaD, and icaR) as well as the virulence gene Hla. In conclusion, this study demonstrates that Glb has a significant inhibitory effect on biofilm activity and is expected to be a good antibiofilm drug.