Role of LuxS/AI-2 quorum sensing in Staphylococcus aureus biofilm formation, intestinal damage and pathogenesis in loach (Misgurnus anguillicaudatus)

Staphylococcus aureus, a prevalent opportunistic pathogen, produces virulence factors that significantly threaten the health of aquatic animals and humans. The quorum sensing (QS) system is crucial for regulating virulence factor expression in pathogenic bacteria. However, the function by which QS regulates S. aureus intestinal colonization in aquatic animals and its subsequent adverse effects on the host have not been fully characterized. Here, we investigated the role of the LuxS/autoinducer-2 (AI-2) QS system in S. aureus strain SA, focusing on its impact on virulence factor expression, intestinal colonization, and host pathology. Using CRISPR-Cas9 technology, we successfully constructed the luxS gene deletion mutant strain SAΔluxS and its corresponding gene complementation strain SAΔluxS (luxS). Strain SAΔluxS exhibited impaired AI-2 synthesis but showed no significant changes in virulence factors such as enterotoxins, bacteriocins, and motility. However, its biofilm formation capacity was enhanced, primarily due to increased extracellular polysaccharide content within the biofilms. Exogenous addition of c-di-AMP led to enhanced biofilm formation in wild-type strain SA, and the elevated c-di-AMP levels in strain SAΔluxS were primarily attributed to reduced gdpP expression. Furthermore, LuxS/AI-2-mediated QS negatively regulated intestinal colonization of S. aureus and mitigated S. aureus-induced intestinal permeability, tissue disruption, and inflammatory response in loach (Misgurnus anguillicaudatus). These findings provide valuable insights into the mechanisms of S. aureus pathogenesis and contribute to developing novel strategies to prevent and control S. aureus infections in aquatic animals.