Chronic wounds, particularly those stubbornly resistant to treatment, may have a surprising culprit: lactic acid produced by a common bacterium, Enterococcus faecalis. New research from the Singapore-MIT Alliance for Research and Technology (SMART), in collaboration with several institutions, reveals how this bacterium actively suppresses the human immune response, creating an environment where infection can thrive. This discovery offers a potential new avenue for developing therapies that go beyond traditional antibiotics, addressing a growing global health challenge.
For patients suffering from conditions like diabetic foot ulcers or post-surgical infections, the struggle to heal can be prolonged and debilitating. These chronic wounds place a significant burden on healthcare systems and, in severe cases, can lead to amputation. Understanding the mechanisms that contribute to their persistence is crucial for improving patient outcomes. The research, published in the journal Cell Host &. Microbe, sheds light on a previously underappreciated tactic employed by E. Faecalis – the strategic release of lactic acid to effectively “silence” the body’s natural defenses.
How Enterococcus faecalis Subverts the Immune System
Enterococcus faecalis is a bacterium frequently found in the human gut, but it can also colonize wounds, especially those that are leisurely to heal. Researchers have long known that certain bacteria can interfere with immune function, but the precise mechanisms were often unclear. This new study demonstrates that E. Faecalis doesn’t simply withstand the immune system; it actively suppresses it. The key lies in the large amounts of lactic acid the bacterium releases into the surrounding tissue. This acid lowers the pH of the wound environment, creating conditions unfavorable to immune cell activity.
The research team discovered that lactic acid impacts immune cells, specifically macrophages, in two key ways. Macrophages are critical components of the immune system, responsible for engulfing and destroying pathogens. Lactic acid enters these cells via a transporter protein called MCT-1 and also binds to a receptor on the cell surface known as GPR81. By targeting both pathways, E. Faecalis effectively disrupts the signaling cascades within macrophages, hindering their ability to respond to the infection. This disruption specifically impacts the NF-κB pathway, a crucial signaling pathway for triggering immune defenses. As detailed in a related study published in Infect Immun in December 2025, E. Faecalis also has the ability to persist and replicate *inside* neutrophils, further complicating immune response.
Evidence from Laboratory and Animal Models
To confirm their findings, the researchers conducted experiments using mouse models. They found that strains of E. Faecalis genetically engineered to be unable to produce lactic acid were cleared more quickly from wounds and triggered a much stronger immune response. This demonstrated a direct link between lactic acid production and immune suppression. The study revealed that the weakened immune environment created by E. Faecalis makes wounds more susceptible to colonization by other bacteria, such as Escherichia coli. This explains why chronic wounds are often polymicrobial, meaning they are infected with multiple species of bacteria, making them even more difficult to treat.
“Our study suggests that chronic wound infections persist not only due to the fact that of antibiotic resistance, but also because the immune system is suppressed at the infection site,” explained Dr. Ronni da Silva, a researcher involved in the study. “The buildup of lactic acid effectively silences key immune signals, preventing macrophages from responding properly.” Professor Kimberly Kline added that the findings provide a deeper understanding of the complex interplay between bacteria and the host immune system, potentially paving the way for novel treatment strategies.
Beyond Antibiotics: New Therapeutic Approaches
The implications of this research extend beyond simply identifying a bacterial mechanism. It opens up possibilities for developing therapies that target the bacterium’s ability to suppress the immune system, rather than solely relying on antibiotics. The researchers suggest several potential approaches, including therapies designed to reduce acidity in wounds or to block the pathways used by lactic acid to inhibit immune cells. Related research from SMART, published in August 2023, identified the enzyme RlmN, which senses chemical and environmental stresses in bacteria, as a potential target for drug development.
The Role of Lactic Acid in Polymicrobial Infections
The study’s findings are particularly relevant to polymicrobial infections, where multiple bacterial species coexist within a wound. By suppressing the immune response, E. Faecalis creates a permissive environment for other pathogens to establish themselves, exacerbating the infection and hindering healing. This is a common scenario in chronic wounds, where a complex interplay of bacterial species often contributes to the persistent inflammation and tissue damage.
Future Research and Clinical Translation
The researchers emphasize that further work is needed to validate these findings in human samples and to translate them into effective clinical treatments. Future studies will focus on investigating the role of lactic acid in human wound infections and on developing and testing novel therapeutic strategies. The team is also exploring the potential of using biomarkers to identify patients who are most likely to benefit from these new approaches. The next step involves preclinical studies to assess the safety and efficacy of potential therapies before moving to human clinical trials.
Key Takeaways
- Enterococcus faecalis suppresses the immune response in chronic wounds by releasing lactic acid.
- Lactic acid disrupts macrophage function by interfering with key signaling pathways, including NF-κB.
- The weakened immune environment created by E. Faecalis promotes the colonization of other bacteria.
- Targeting the bacterium’s ability to suppress immunity offers a promising new therapeutic strategy.
- Further research is needed to validate these findings in human studies and develop effective treatments.
This research represents a significant step forward in our understanding of chronic wound infections and offers hope for developing more effective treatments for patients who suffer from these debilitating conditions. The focus on modulating the immune response, rather than solely relying on antibiotics, could revolutionize the way we approach wound care and improve outcomes for millions of people worldwide. The researchers plan to continue their investigations, with the goal of bringing these promising new therapies to the clinic in the coming years.
Researchers will continue to validate these results in human samples and advance toward preclinical studies. Stay tuned for further updates on this important research.
Keep reading