Analysis of myeloperoxidase activity in wound fluids as a marker of infection

Background: Neutrophilic polymorphonuclear leukocytes play a crucial role in the host defence against bacterial and fungal infections. They participate in the inflammatory response through the liberation of peptides and enzymes like myeloperoxidase (MPO). Therefore, MPO has a potential as a marker enzyme for the diagnosis of wound infection. Methods: Substrate specificities and reaction pathways of MPO were investigated for new MPO substrates: crystal violet, leuco crystal violet, fast blue RR (4-benzoylamino-2,5-dimethoxybenzenediazonium chloride hemi(zinc chloride) salt) and various systematically substituted model substrates based on 2,7-dihydroxy-1-(4-hydroxyphenylazo)naphtalene-3,6-disulphonic acid. In addition, fast blue RR was covalently bound to siloxanes allowing immobilization of the substrate, while cellobiosedehydrogenase was integrated for generation of hydrogen peroxide required by MPO. Results: Elevated concentrations of MPO were found in infected wounds compared with non-infected wounds (92.2 +/- 45.0 versus 1.9 +/- 1.8 U/mL). Various soluble and immobilized substrates were oxidized by MPO in wound samples and the influence of substrate structure and reaction pathways were elucidated for selected compounds. Conclusions: Incubation of different MPO substrates with infected wound fluid samples resulted in a clear colour change in the case of elevated MPO concentrations, thus allowing early diagnosis of wound infection.