biostudies-literatureUnknownAntypas HSwiss National Science FoundationNIAID NIH HHSInfective endocarditis (IE) is a life-threatening biofilm-associated infection, yet the factors driving biofilm formation remain poorly understood. Here, we identified the Fsr quorum sensing (QS) system of <i>Enterococcus faecalis</i> as a potent negative regulator of IE pathogenesis. Using microfluidic and <i>in vivo</i> models, we show that Fsr is induced in late IE when bacteria become shielded from blood flow. Deleting Fsr altered biofilm metabolism and promoted robust biofilm growth and gentamicin tolerance <i>in vivo</i>. Furthermore, Fsr inactivation attenuated inflammation by disrupting IL-1β cleavage and activation via the Fsr-regulated gelatinase (<i>gelE</i>), allowing biofilm to grow unchecked by the immune system. Consistent with our pre-clinical findings, analysis of two IE pbioRxiv : the preprint server for biology2025.02.07.636843https://www.ebi.ac.uk/biostudies/studies/S-EPMC11839028biostudies-literatureFsr quorum sensing system restricts biofilm growth and activates inflammation in enterococcal infective endocarditis.PMC11839028204343211422310030R21 AI164018Neo CJYBrugger SDSchmidtchen VZinkernagel ASDA Silva RAGNg KKFWong JJManzano CWong SLTan RJWTanoto FRLi YKline KAPethe KWinter CCRadhesh SMAntypas HStaiger WIHasse BVAN Tyne DfalseFsr quorum sensing system restricts biofilm growth and activates inflammation in enterococcal infective endocarditis.Infective endocarditis (IE) is a life-threatening biofilm-associated infection, yet the factors driving biofilm formation remain poorly understood. Here, we identified the Fsr quorum sensing (QS) system of <i>Enterococcus faecalis</i> as a potent negative regulator of IE pathogenesis. Using microfluidic and <i>in vivo</i> models, we show that Fsr is induced in late IE when bacteria become shielded from blood flow. Deleting Fsr altered biofilm metabolism and promoted robust biofilm growth and gentamicin tolerance <i>in vivo</i>. Furthermore, Fsr inactivation attenuated inflammation by disrupting IL-1β cleavage and activation via the Fsr-regulated gelatinase (<i>gelE</i>), allowing biofilm to grow unchecked by the immune system. Consistent with our pre-clinical findings, analysis of two IE p2025-01-01T00:00:00Z2025 Feb2026-04-08T19:22:06.862Z2025-04-06T23:41:12.917ZS-EPMC118390283997495710.1101/2025.02.07.636843