Luteolin attenuates the pathogenesis of Staphylococcus aureus by interfering with the agr system

Staphylococcus aureus is a serious human pathogen that causes a wide variety of infectious diseases with high morbidity and mortality. Luteolin was recently shown to inhibit biofilm formation and reduce the production of virulence factors and the transcription of agrA in S. aureus. Given the broad impacts of the agr quorum-sensing system on the biofilm formation and virulence factors of S. aureus, this study aimed to investigate the effects of luteolin on the agr system and pathogenicity of S. aureus. Here, we show that at subminimal inhibitory concentrations (sub-MICs) that have no effect on bacterial growth, luteolin can markedly inhibit the adhesion and biofilm formation of both wild-type (WT) and agr mutant strains of S. aureus strain Newman. The hemolytic activity and toxin protein levels were markedly decreased in the culture supernatants of luteolin-treated WT strain but not the luteolin-treated agr mutant strain. qRT-PCR analysis showed that upon luteolin treatment, the expression of genes involved in virulence and biofilm formation was downregulated in the WT S. aureus strain, and the inefficacy of luteolin with respect to the virulence factors of only the agr mutant confirmed the agr-mediated antivirulence potential of luteolin. Furthermore, treatment with sub-MIC luteolin attenuated human alveolar epithelial A549 cell injury caused by the WT Newman strain and protected mice from pneumonia caused by the WT strain, but these effects were not observed with the agr mutant strain. These findings indicate that luteolin is a promising compound that interferes with the agr system and can be developed into novel therapeutic drugs against S. aureus infections.