How Bacteria Disarm Immune Defenses in Chronic Wound Infections

Chronic wound infections are a major burden on healthcare systems because they require prolonged, resource-intensive care and are associated with severe outcomes, like amputation. What makes them particularly difficult to resolve is that they are often not simple infections; they are complex, and a lot of times [they are] polymicrobial ecosystems—multi-species communities where diverse microorganisms (bacteria, fungi, viruses) live in close proximity— embedded in biofilms.

These biofilms protect bacteria from antibiotics and immune responses, while different species may cooperate metabolically to enhance persistence.

On top of that, the host environment is fundamentally dysregulated, with chronic inflammation and impaired healing. Our work adds to this by showing that pathogens like E. faecalis can actively reprogram host immunity through metabolic outputs like lactic acid to suppress macrophage responses. So, rather than just resisting treatment, these infections actively create a permissive niche for long-term survival.

Altogether, this helps to explain why conventional antibiotic approaches often fail and highlights the need for host-directed and anti-biofilm therapies.

Diabetes shifts the balance toward microbial persistence through a combination of impaired immune function, metabolic dysregulation, and defective tissue repair. Innate immune cells like macrophages and neutrophils are less effective at clearing bacteria, while the tissue environment becomes more permissive due to hyperglycemia, hypoxia, and poor vascularization.

Importantly, this altered metabolic landscape likely converges and cross-talks with bacterial strategies. In our work, we show that E. faecalis produces lactic acid, which suppresses macrophage activation. In a diabetic context, where metabolism is already dysregulated, these immunosuppressive effects could well be amplified.

So, rather than a simple failure of defense, diabetes creates a condition where host and pathogen metabolism converge to promote long-term microbial persistence.

The local wound environment is an important determinant of both microbial behavior and immune function. Factors like pH, oxygen levels, and metabolite availability shape bacterial virulence, biofilm formation, and metabolic activity, while simultaneously reprogramming and shaping immune responses.

Our research has shown that lactic acid released by E. faecalis can actively modify this environment by producing lactic acid to suppress macrophage activation through specific host signaling pathways. This creates a feedback loop where the environment becomes increasingly permissive to bacterial persistence. So, the environment should be seen as an active driver of chronic infection and a key therapeutic target.

Our identification of lactic acid-mediated immune suppression adds to our current knowledge of chronic wound pathology. Rather than viewing these infections as simply resistant to clearance, we show that bacteria can actively suppress host immunity through metabolic outputs.

More broadly, our work introduces the concept of metabolic immune evasion, where bacterial metabolites help to reshape the local environment and host responses to promote persistence. This contributes to shifting the field toward targeting not just the pathogen, but also the metabolic interactions between host and microbe as a therapeutic strategy.

Our findings support the development of, for example, host-directed therapies that restore immune function rather than relying solely on antimicrobial activity. Our study identifies a defined axis of immune suppression that can be studied in the future to be therapeutically targeted to prevent macrophage inhibition.

We also found that this dysfunction is not irreversible. Using a drug that overrides the blockage caused by E. faecalis was sufficient to promote bacterial clearance in a wound mouse model, demonstrating that macrophages in wound infections are not intrinsically defective; they are actively suppressed but can be reprogrammed. This highlights this drug as a potential therapeutic node to rebalance immune responses in this context.

Together, these findings support a model where infection outcomes are determined by the balance between bacterial immunosuppressive signals and host activating pathways. Therapeutically, this opens the door to combination strategies that both relieve suppression, for instance, by targeting lactic acid signaling, and actively restore immune function. However, further studies are needed to fully establish these pathways as therapeutic targets in humans.

Additionally, wounds are particularly good candidates for targeted delivery approaches such as topical treatments or nanoparticles.