UNLABELLED: Quorum sensing (QS) is widely utilized by both bacteria and fungi to mediate cell-cell communication. Previous studies have demonstrated that the indole derivative indole-3-ethanol (also known as tryptophol) controls morphogenesis as a QS molecule in fungi. However, whether this QS signal is involved in the modulation of biological functions in bacteria remains unknown. Here, we report that indole-3-ethanol controls the biological functions and pathogenicity of subsp. ATCC 13047. The biosynthesis of indole-3-ethanol is performed by YjgB (ECL_RS22935), an alcohol dehydrogenase. Deletion of results in impaired biological functions and virulence. Furthermore, we revealed that indole-3-ethanol from reduces the competitive fitness of by inhibiting its biofilm formation, extracellular polysaccharide synthesis, and virulence. Given that both and are common human intestinal microbes, our results highlight the critical roles of indole-3-ethanol in both intraspecies signaling and interspecies communication in bacteria. IMPORTANCE: Quorum sensing is a cell-cell communication mechanism widely employed by bacteria to control various biological functions and pathogenicity. In this study, we demonstrated that employs indole-3-ethanol as a quorum-sensing signal to control biological functions and virulence. We also revealed that indole-3-ethanol from effectively inhibits biofilm formation and virulence in . Our findings not only suggest the important role of indole-3-ethanol in the regulation of the pathogenicity of but also provide new insights into the development of indole-3-ethanol as an anti-virulence agent against .