Ismail, M. H. | bioRxiv Science

bioRxiv2025

Enterococcus faecalis-derived lactic acid facilitates persistent and polymicrobial wound infections by suppressing macrophage activation

Macrophage activation is essential for innate immunity, and its suppression enables pathogen persistence. We show that Enterococcus faecalis suppresses macrophage activation through lactic acid-mediated extracellular acidification. Mutants lacking lactate dehydrogenase (ldh), and thus unable to acidify the environment, fail to inhibit NF-{kappa}B. E. faecalis-derived lactic acid acts via MCT-1 and GPR81 through two distinct but complementary mechanisms that culminate in the reduction of NF-{kappa}B activity. Lactic acid acts through MCT-1 to inhibit ERK and STAT3 phosphorylation, leading to reduced STAT3 binding to the Myd88 promoter, and reduced MyD88 protein levels. Lactic acid signaling to GPR81 mediates the phosphorylation of the transcriptional factor YAP, ultimately attenuating NF-{kappa}B signaling. In a murine wound infection model, this lactic acid-driven immunosuppressive niche enables prolonged E. faecalis persistence and enhances the fitness of co-infecting bacteria such as Escherichia coli. These findings reveal how bacterial lactic acid subverts innate immunity to support chronic and polymicrobial infections. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=140 SRC="FIGDIR/small/635924v2_ufig1.gif" ALT="Figure 1"> View larger version (34K): org.highwire.dtl.DTLVardef@2e1565org.highwire.dtl.DTLVardef@17eaf85org.highwire.dtl.DTLVardef@356139org.highwire.dtl.DTLVardef@821581_HPS_FORMAT_FIGEXP M_FIG C_FIG Highlights- E. faecalis lactate dehydrogenase mutants fail to acidify the environment and cannot suppress NF-{kappa}B signaling. - Lactic acid is necessary and sufficient to drive NF-{kappa}B suppression in macrophages. - Lactic acid NF-{kappa}B suppression is relayed through two complementary routes: MCT- 1 transport and the lactate sensor GPR81. - MCT-1-dependent signaling blunts ERK/STAT3 phosphorylation, lowering MyD88 levels; whereas GPR81 drives YAP phosphorylation, reducing NF-{kappa}B activation. - E. faecalis-derived lactic acid drives immunosuppression, potentiates persistence, and promotes multi-species wound infection in vivo.

microbiology↗

bioRxiv2022

Purine and carbohydrate availability drive Enterococcus faecalis fitness during wound infection

Enterococcus faecalis is commonly isolated from a variety of wound types. Despite its prevalence, the pathogenic mechanisms of E. faecalis during wound infection are poorly understood. Using a mouse wound infection model, we performed in vivo E. faecalis transposon sequencing and RNA sequencing to identify fitness determinants that are crucial for replication and persistence of E. faecalis during wound infection. We found that E. faecalis purine biosynthesis genes are important for bacterial replication during the early stages of wound infection, a time when purine metabolites are rapidly consumed by E. faecalis within wounds. We also found that the E. faecalis MptABCD phosphotransferase system (PTS), involved in the import of galactose and mannose, is crucial for E. faecalis persistence within wounds of both healthy and diabetic mice, especially when carbohydrate availability changes throughout the course of infection. During in vitro growth with mannose as the sole carbohydrate source, shikimate and purine biosynthesis genes were downregulated in the OG1RF {Delta}mptD mutant compared to the isogenic wild-type strain, suggesting a link between mannose transport, shikimate, and purine biosynthesis. Together, our results suggest that dynamic and temporal microenvironment changes at the wound site affects pathogenic requirements and mechanisms of E. faecalis and raise the possibility of lowering exogenous purine availability and/or targeting galactose/mannose PTS to control wound infections. IMPORTANCEAlthough E. faecalis is a common wound pathogen, its pathogenic mechanisms during wound infection are unexplored. Here, combining a mouse wound infection model with in vivo transposon and RNA sequencing approaches, we identified the E. faecalis purine biosynthetic pathway and galactose/mannose MptABCD phosphotransferase system as essential for E. faecalis acute replication and persistence during wound infection, respectively. The essentiality of purine biosynthesis and the MptABCD PTS is driven by the rapid consumption of purine metabolites by E. faecalis during acute replication and changing carbohydrate availability during the course of wound infection. Overall, our findings reveal the importance of the wound microenvironment in E. faecalis wound pathogenesis and how these metabolic pathways can be targeted to better control wound infections.

microbiology↗