The growth of Escherichia coli cultures under the influence of pheomelanin nanoparticles and a chelant agent in the presence of light

Growing concern of antibiotic resistance has increased research efforts to find nonspecific treatments to inhibit pathogenic microorganisms. In this regard, photodynamic inactivation is a promising method. It is based on the excitation of a photosensitizer molecule (PS) with UV-Vis radiation to produce reactive oxygen species. The high reactivity of such species nearby the PS leads to oxidation of bacterial cell walls, lipid membranes (lipid peroxidation), enzymes, and nucleic acids, eventually producing cell death. In the last decade, many studies have been carried out with different photosensitizers to suppress the growth of bacteria, fungi, viruses, and malignant tumors. Here, our main motivation is to employ pheomelanin nanoparticles as sensitizers for inhibiting the growth of the Gram-negative bacteria E. coli, exposed to blue and UVA radiation. In order to perform our experiments, we synthesized pheomelanin nanoparticles from L-DOPA and L-cysteine through an oxidation process. We carried out experiments at different particle concentrations and different energy fluences. We found that cultures exposed to UVA at 166 mu g/mL and 270 J/cm(2), in conjunction with ethylenediaminetetraacetic acid (EDTA) as an enhancer, decreased in the viable count 5 log10. Different reactive oxygen species (singlet oxygen, hydroxyl radicals, and peroxynitrates) were detected using different procedures. Our results suggest that the method reported here is effective against E. coli, which could encourage further investigations in other type of bacteria.

Automated summary

Photodynamic inactivation is a promising method that utilizes photosensitizers to generate reactive oxygen species and inhibit the growth of pathogenic microorganisms. In this study, pheomelanin nanoparticles were used as sensitizers to successfully inhibit the growth of E. coli. The results suggest that this method is effective against E. coli and could potentially be applied to other bacteria.