Role of the fsr Quorum-Sensing System in Enterococcus faecalis Bloodstream Infection.

Enterococcus faecalis is an important intestinal colonizing bacteria and can cause various tissue infections, including invasive blood infection (BI). The annual incidence of E. faecalis BI has been estimated to be ~4.5 per 100,000, with a fatality rate that can reach 20%. However, whether bacterial colonization or invasive infections are tissue based has not been thoroughly studied. In this study, we analyzed 537 clinical isolates from 7 different tissues to identify the key genomic elements that facilitate the colonization and invasive infection of E. faecalis. Comparative genomic analysis revealed that the BI E. faecalis isolates had the largest genome size but the lowest GC content, fsr quorum-sensing system genes were enriched in the BI E. faecalis, and the fsr gene cluster could enhance biofilm formation and serum resistance ability. Our findings also provide deep insight into the genomic differences between different tissue isolates, and the fsr quorum-sensing systems could be a key factor promoting E. faecalis invasion into the blood. IMPORTANCE First, we conducted an advanced study on the genomic differences between colonizing and infecting E. faecalis, which provides support and evidence for early and accurate diagnoses. Second, we discovered that fsr was significantly associated with blood infections, which also provides additional information for studies exploring the invasiveness of E. faecalis. Most importantly, we found that fsr played an important role in both biofilm formation and serum resistance ability in E. faecalis.