LL-37 and Wound Biofilm Research: Antimicrobial Peptide Activity, Biofilm Disruption and Chronic Wound Biology UK 2026

This article is for Research Use Only. LL-37 is a research peptide not approved for human therapeutic use. All information is provided for scientific and educational purposes only.

Introduction: Biofilm, Chronic Wounds, and the Antimicrobial Peptide Research Opportunity

Chronic wounds — defined as wounds failing to progress through normal healing phases within 12 weeks — represent a significant global health research challenge. Diabetic foot ulcers, venous leg ulcers, pressure injuries, and surgical site infections account for a substantial burden of antimicrobial resistance-related morbidity. A defining feature of virtually all chronic wounds is the presence of polymicrobial biofilm: structured communities of bacteria encased in an extracellular polymeric substance (EPS) matrix that confers profound tolerance to antibiotics and host immune defences.

LL-37 — the sole cathelicidin in the human antimicrobial peptide (AMP) arsenal, derived from the C-terminal processing of hCAP-18 (human cationic antimicrobial protein 18) — has emerged as a particularly relevant research candidate for biofilm biology. Unlike most conventional antibiotics that target planktonic (free-floating) bacteria, LL-37 has documented activity against established biofilms of clinically relevant wound pathogens, disrupts biofilm structural integrity, and modulates the host immune response in wounded tissue. Understanding LL-37’s biofilm research biology requires integrating its direct antimicrobial mechanisms with its immunomodulatory and wound healing properties.

Biofilm Pathophysiology in Chronic Wounds

Wound biofilms develop in a structured sequence: initial bacterial adhesion to the wound bed matrix (mediated by bacterial surface adhesins binding fibronectin, collagen, and fibrinogen components of the wound extracellular matrix); micro-colony formation and quorum sensing-triggered EPS matrix production; and maturation of the three-dimensional biofilm architecture with internal water channels, nutrient gradients, and phenotypically diverse bacterial subpopulations.

The EPS matrix of wound biofilms is a formidable barrier comprising polysaccharides (alginate, Pel, Psl in Pseudomonas aeruginosa; poly-N-acetylglucosamine in Staphylococcus aureus), extracellular DNA (eDNA released from lysed bacteria), proteins (including surface adhesins and proteases), and bacterial outer membrane vesicles. This matrix impedes antibiotic penetration by physical exclusion and charge-based repulsion; produces enzymatic antibiotic degradation (β-lactamases in the matrix microenvironment); and creates metabolic gradients that generate persister cells — metabolically dormant bacteria with extreme antibiotic tolerance.

Common wound biofilm pathogens include Pseudomonas aeruginosa (which produces the most extensively studied EPS matrix), Staphylococcus aureus and methicillin-resistant S. aureus (MRSA), Enterococcus faecalis, Enterobacteriaceae species, and polymicrobial consortia where interbacterial interactions produce emergent resistance phenotypes more severe than any individual species. The research challenge is developing agents active against all these organisms and their biofilm forms — a challenge where LL-37’s broad-spectrum amphipathic mechanism offers potential advantages.

LL-37 Mechanism of Biofilm Disruption

LL-37’s anti-biofilm activity operates through distinct mechanisms from its planktonic bactericidal action. Against planktonic bacteria, LL-37 adopts an amphipathic α-helical conformation upon contact with bacterial membranes, inserts into the phospholipid bilayer, and disrupts membrane integrity through carpet/toroidal pore models — producing rapid osmotic lysis. Against established biofilms, the mechanisms are more complex and partially distinct:

EPS matrix disruption: LL-37 interacts with the anionic components of the EPS matrix (particularly eDNA and anionic polysaccharides) through electrostatic interactions, competing for matrix-binding sites that normally provide EPS structural integrity. Research using confocal laser scanning microscopy (CLSM) with fluorescent LL-37 and live/dead bacterial staining demonstrates that sub-MIC concentrations of LL-37 can penetrate and partially disrupt biofilm structure before achieving bactericidal activity — a “loosening” effect that may enhance antibiotic co-penetration.

Quorum sensing inhibition: LL-37 has demonstrated inhibitory effects on quorum sensing (QS) signalling systems in P. aeruginosa, including the las and rhl systems that regulate EPS production, virulence factor expression, and biofilm maturation. By interfering with N-acyl homoserine lactone (AHL) signalling, LL-37 may disrupt the bacterial communication that coordinates biofilm maturation and maintenance — a mechanism with potential synergistic implications when combined with QS-inhibitor antibiotics.

Prevention of biofilm formation: At sub-MIC concentrations, LL-37 inhibits initial bacterial surface adhesion, impairing micro-colony formation — the first step in biofilm establishment. This anti-adhesion property is mechanistically distinct from biofilm disruption and suggests LL-37 may be most effective as a prophylactic coating agent for wound dressings or implant surfaces in research contexts, rather than purely as a disrupting agent for established biofilms.

eDNA targeting: Extracellular DNA is a structural scaffold component of many wound biofilms and is specifically targeted by LL-37’s net positive charge (at physiological pH). Research demonstrates that DNase I (which degrades eDNA) and LL-37 act synergistically against S. aureus and P. aeruginosa biofilms — with combined treatment producing greater reduction in biofilm biomass than either agent alone. This eDNA-targeting mechanism provides a rationale for combination research strategies.

LL-37 Activity Against Specific Wound Pathogens

Pseudomonas aeruginosa: The archetypical wound biofilm former, P. aeruginosa produces copious alginate EPS and is intrinsically resistant to many antibiotics. LL-37 demonstrates biofilm-inhibitory activity against P. aeruginosa at concentrations achievable at wound surfaces, though activity is substantially reduced in media supplemented with cations (Ca²⁺, Mg²⁺) or mucins that quench LL-37’s cationic activity. Research in CF (cystic fibrosis) lung biofilm models — where P. aeruginosa chronically colonises — has extensively characterised LL-37 resistance mechanisms (including the ArnT lipid A modification that reduces membrane net negative charge) relevant to wound biofilm contexts.

Staphylococcus aureus / MRSA: S. aureus wound biofilms are characterised by poly-N-acetylglucosamine (PNAG) as the primary EPS component, though biofilm-positive strains are highly variable. LL-37 shows bactericidal activity against planktonic MRSA at concentrations consistent with wound-surface delivery, though established S. aureus biofilms show variable susceptibility. S. aureus produces several LL-37 resistance mechanisms including aureolysin (a metalloprotease that degrades LL-37), DltABCD-mediated D-alanylation of teichoic acids (reducing negative surface charge), and staphylokinase (a proteolytic cleavage enzyme). Understanding these resistance mechanisms is critical for rational research design of LL-37 combination or stability-enhanced approaches.

Polymicrobial biofilms: Chronic wounds typically harbour polymicrobial biofilms rather than single-species infections. Interbacterial interactions in polymicrobial biofilms — including EPS cross-protection, antibiotic-degrading enzyme sharing, and cooperative virulence factor expression — produce emergent properties that make monotherapy research predictions unreliable. LL-37 research in polymicrobial biofilm models (using established polymicrobial combinations such as S. aureus + P. aeruginosa, or S. aureus + Candida albicans) provides ecologically valid data on AMP activity in the wound environment.

Immunomodulatory Properties Relevant to Chronic Wound Biology

Beyond direct antimicrobial activity, LL-37’s immunomodulatory properties are mechanistically important in the chronic wound research context. Chronic wounds are characterised by a dysregulated inflammatory state: persistent neutrophil infiltration producing proteolytic enzyme (MMP, elastase) overexpression that degrades growth factors and ECM components; macrophage polarisation skewed toward M1 pro-inflammatory phenotype; and failure to transition to the proliferative and remodelling healing phases.

LL-37 modulates this inflammatory dysregulation through several mechanisms:

• MMP regulation: LL-37 can both stimulate (in keratinocytes, promoting wound edge migration) and suppress (in macrophages, reducing MMP-9 overproduction) MMP activity in contextual fashion — suggesting wound-phase-appropriate effects
• Macrophage polarisation: LL-37 promotes M2 macrophage polarisation (anti-inflammatory, pro-reparative) in some experimental contexts by suppressing NF-κB-driven TNF-α and IL-6 production while maintaining phagocytic clearance activity
• Angiogenesis promotion: LL-37 stimulates VEGF production and endothelial cell migration, promoting neovascularisation essential for granulation tissue formation in wound healing — a pro-regenerative effect orthogonal to its antimicrobial properties
• Keratinocyte migration: LL-37 activates ErbB2 receptor transactivation in keratinocytes, stimulating their migration and proliferation for re-epithelialisation — the final wound closure phase that fails in chronic wounds

LL-37 Delivery Systems in Wound Research

A key research challenge for LL-37 in wound biology is delivery in a form that maintains bioactivity at the wound surface in the presence of wound fluid, serum proteases, salt concentrations, and pH variation. Native LL-37 is susceptible to proteolytic degradation by wound proteases (elastase, MMP-7, aureolysin) that are highly expressed in chronic wound environments — one reason why endogenous LL-37 levels, while elevated in wound tissue, may be insufficient to control biofilm. Research into LL-37 delivery systems for wound applications includes:

• Hydrogel incorporation: pH-responsive or thermoresponsive hydrogels enabling sustained LL-37 release with protection from protease degradation
• Nanoparticle encapsulation: PLGA, lipid, or chitosan nanoparticles providing protease-protective LL-37 delivery with controlled release kinetics
• Wound dressing integration: LL-37 immobilised onto electrospun fibre dressings or cellulose-based wound covers for contact-activated release
• LL-37 fragments and analogues: Shorter LL-37 fragments (P60.4Ac, SAAP-148, CaD24) with improved protease resistance and maintained or enhanced anti-biofilm activity

Antimicrobial Resistance Research Context

LL-37 is of particular research interest in the antimicrobial resistance (AMR) context. Unlike conventional antibiotics targeting specific bacterial enzymes or structural components (cell wall synthesis, ribosomal translation, DNA gyrase), LL-37’s membrane-disruption mechanism exerts selection pressure on membrane lipid composition and surface charge — properties that are energetically costly for bacteria to modify rapidly. This mechanistic basis has led to the hypothesis that resistance to cathelicidins develops more slowly than resistance to conventional antibiotics, making LL-37 and its derivatives research candidates for addressing the AMR crisis in chronic wound contexts specifically.

Research into LL-37 resistance mechanisms — including biofilm-based phenotypic tolerance (not genetic resistance), lipid A modification in P. aeruginosa, and protease-mediated degradation in S. aureus — is essential for developing LL-37-based approaches that anticipate and counteract resistance evolution. Combination research strategies pairing LL-37 with conventional antibiotics at sub-MIC concentrations — exploiting the biofilm-penetration enhancing and QS-inhibitory properties of LL-37 alongside the bactericidal activity of standard antibiotics — represent a practical AMR research direction with potential translational relevance.

Regulatory and Research Framing

LL-37 is supplied for research use only under MHRA research exemptions. It is not approved for clinical wound management or antimicrobial therapy in the UK. All research involving in vivo wound or infection models must comply with the Animals (Scientific Procedures) Act 1986 and require Home Office project licence authorisation. In vitro biofilm research using LL-37 falls under standard laboratory safety frameworks without requiring specific regulatory approval beyond institutional biosafety assessment for pathogen handling. No wound treatment protocols, clinical antimicrobial recommendations, or clinical dosing guidance are derived from this overview.