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.
Wound infection is a severe complication causing delayed healing and risks for patients. Conventional methods of diagnosis for infection involve error-prone clinical description of the wound and time-consuming microbiological tests. More reliable alternatives are still rare, except for invasive and unaffordable gold standard methods. This review discusses the diversity of new approaches for wound infection determination. There has been progress in the detection methods of microorganisms, including the assessment of the diversity of the bacterial community present in a wound, as well as in the elaboration of specific markers. Another interesting strategy involves the quantification of enzyme activities in the wound fluid secreted by the immune system as response to infection. Color-changing substrates for these enzymes consequently have been shown to allow detection of an infection in wounds in a fast and easy way. Promising results were also delivered in measuring pH changes or detecting enhanced amounts of volatile molecules in case of infection. A simple and effective infection detection tool is not yet on the market, but innovative ideas pave the way for the investigation of fast and easy point-of-care devices.
A gelatinase-based device for fast detection of wound infection was developed. Collective gelatinolytic activity in infected wounds was 23 times higher (p ≤ 0.001) than in noninfected wounds and blisters according to the clinical and microbiological description of the wounds. Enzyme activities of critical wounds showed 12-fold elevated enzyme activities compared with noninfected wounds and blisters. Upon incubation of gelatin-based devices with infected wound fluids, an incubation time of 30 minutes led to a clearly visible dye release. A 32-fold color increase was measured after 60 minutes. Both matrix metalloproteinases and elastases contributed to collective gelatinolytic enzyme activity as shown by zymography and inhibition experiments. The metalloproteinase inhibitor 1,10-phenanthroline (targeting matrix metalloproteinases) and the serine protease inhibitor phenylmethlysulfonyl fluoride (targeting human neutrophil elastase) inhibited gelatinolytic activity in infected wound fluid samples by 11-37% and 60-95%, respectively. Staphylococcus aureus and Pseudomonas aeruginosa, both known for gelatinase production, were isolated in infected wound samples.
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