Spent coffee ground disrupts Listeria monocytogenes biofilm formation through inhibition of motility and adhesion via quorum sensing regulation

Spent coffee grounds (SCGs) have been explored for use as various bioresources, such as biofuels, and are known to possess biological functions, including antioxidant activity. However, the antibiofilm properties of SCGs against pathogenic bacteria have not been fully investigated. Therefore, this study aimed to highlight the inhibitory effects of SCG extract (SCGE) on biofilm formation in Listeria monocytogenes and investigated the underlying mechanisms. Treatment with SCGE disrupted both biofilm formation and architecture in L. monocytogenes. Furthermore, SCGE reduced autoaggregation and surface hydrophobicity. However, SCGE did not affect the viability of planktonic L. monocytogenes, suggesting that the decrease in biofilm formation was not attributed to decreased viability. Instead, SCGE downregulated motility- and adhesion-related genes in L. monocytogenes. Furthermore, SCGE impaired the swimming motility of L. monocytogenes. It also impaired adhesion to and invasion of intestinal epithelial cells. Moreover, SCGE suppressed the production of autoinducer-2, indicating the inhibition of quorum sensing signaling. Taken together, these findings suggest that SCGE inhibits biofilm formation in L. monocytogenes by modulating quorum sensing signaling, which regulates bacterial motility and adhesion.