The study shows that the antiseptic polymer PHMB can kill bacteria in human wound fluid and stop the damage caused by Pseudomonas aeruginosa, which normally breaks down important skin proteins and inactivates the natural antimicrobial peptide LL‑37. In simple terms, PHMB protects wounds from bacterial enzymes that would otherwise destroy tissue and neutralize the body's own defenses.

Antimicrobial peptides are important effectors of innate immunity. Bacteria display multiple defence mechanisms against these peptides. For example, Pseudomonas aeruginosa releases potent proteinases that inactivate the human cathelicidin LL-37. Hence, in conditions characterized by persistent bacterial colonization, such as in P. aeruginosa-infected skin wounds, there is a need for efficient means of reducing bacterial load. Here, the effect of the cationic molecule polyhexamethylenebiguanide (PHMB) was evaluated. Infection models in human wound fluid and human skin were established. Radial diffusion methods, bacterial growth and bactericidal assays were used for determination of effects of PHMB on bacteria in the presence of plasma, wound fluid or human skin. At the protein and tissue levels, SDS-PAGE, light microscopy and scanning electron microscopy were used to study the effects of P. aeruginosa infection before and after addition of PHMB. PHMB killed common ulcer-derived bacteria in the presence of human wound fluid. Furthermore, elastase-expressing P. aeruginosa completely degraded wound fluid proteins as well as human skin during infection ex vivo. The infection, and consequent protein degradation, was reversed by PHMB. The ex vivo infection models presented here should be helpful in the screening of novel antimicrobials and constitute a prerequisite for future clinical studies.