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It is generally acknowledged that the age of antibiotics could come to an end, due to their widespread and inappropriate use. Particularly for chronic wounds alternatives are being thought. Antimicrobial Photodynamic Therapy is a potential candidate, and while approved for some indications, such as periodontitis, chronic sinusitis and other niche indications, its use in chronic wounds is not established. To further facilitate the development of Antimicrobial Photodynamic Therapy in chronic wounds we present an easy to use animal model exhibiting the key hallmarks of chronic wounds, based on full-thickness skin wounds paired with an optically transparent cover. The moisture-retaining wound exhibited rapid expansion of pathogen colonies up to 8 days while not jeopardizing the host survival. Use of two bioluminescent pathogens; methicillin resistant Staphylococcus aureus and Pseudomonas aeruginosa permits real time monitoring of the pathogens. The murine model was employed to evaluate the performance of four different photosensitizers as mediators in Photodynamic Therapy. While all four photosensitizers, Rose Bengal, porphyrin TMPyP, New Methylene Blue and TLD1411 demonstrated good to excellent antimicrobial efficacy in planktonic solutions at 1 to 50 µM concentrations, whereas in in vivo the growth delay was limited with 24-48 hr delay in pathogen expansion for methicillin resistant Staphylococcus aureus, and we noticed longer growth suppression of Pseudomonas aeruginosa with TLD1411 mediated Photodynamic Therapy. The murine model will enable developing new strategies for enhancement of Antimicrobial Photodynamic Therapy for chronic wound infections.

Metal-based photosensitizers are of interest as their absorption and chemical binding properties can be modified via the use of different ligands. Ru(2+) based photosensitizers are known to be effective photodynamic therapy (PDT) agents against bacteria, whereas use for oncological indications in vivo has not been demonstrated with the same level of evidence. We present data showing that premixing the Ru(2+)-complex TLD1433 with transferrin increases the molar extinction coefficient, including longer activation wavelengths, reduces photobleaching rates, and reduces the toxicity of the complex improving overall PDT efficacy. As the transferrin receptor is upregulated in most malignancies, premixing the Ru(2+) complex with transferrin converts the active pharmaceutical ingredient TLD1433 into a drug of potentially considerable clinical utility.

Summary Background The introduction of new disinfection and sterilization methods, such as antimicrobial photodynamic therapy, is urgently needed for the healthcare industry, in particular to address the pervasive problem of antibiotic resistance. This study evaluated the efficacy and the mechanisms of photodynamic antimicrobial chemotherapy (PACT), also known as photodynamic inactivation (PDI) of microorganisms, induced by novel Ru(II)-based photosensitizers against Staphylococcus aureus and methicillin-resistant S. aureus strains. Methods The photodynamic antibacterial effects of a new class of Ru(II)-based photosensitizers (TLD1411 and TLD1433) were evaluated against a strain of S. aureus (ATCC 25923) and a methicillin-resistant strain of S. aureus (MRSA, ATCC 33592). Bacterial samples were dosed with a range of photosensitizer concentrations (0.3–12 μM) and exposed to 530 nm light (90 J cm −2 ) in normoxic conditions (ambient atmosphere) and in hypoxic conditions (0.5% O 2 ). Results Both photosensitizers exerted photodynamic inactivation (PDI) of the microorganisms in normoxia, and this activity was observed in the nanomolar regime. TLD1411 and TLD1433 maintained this PDI potency under hypoxic conditions, with TLD1433 becoming even more active in the low-oxygen environment. Conclusion The observation of activity in hypoxia suggests that there exists an oxygen-independent, Type I photoprocess for this new class of compounds in addition to the typical Type II pathway mediated by singlet oxygen. The intrinsic positive charge of the Ru(II) metal combined with the oxygen independent activity demonstrated by this class of photosensitizers presents a new strategy for eradicating both gram-positive and gram-negative bacteria regardless of oxygenation level.

Fast detection of bacterial concentrations is important for the food industry and for healthcare. Early detection of infections and appropriate treatment is essential since, the delay of treatments for bacterial infections tends to be associated with higher mortality rates. In the food industry and in healthcare, standard procedures require the count of colony-forming units in order to quantify bacterial concentrations, however, this method is time consuming and reports require three days to be completed. An alternative is metabolic-colorimetric assays which provide time efficient in vitro bacterial concentrations. A colorimetric assay based on Resazurin was developed as a time kinetic assay (KRA) suitable for bacterial concentration measurements. An optimization was performed by finding excitation and emission wavelengths for fluorescent acquisition. A comparison of two non-related bacteria, foodborne pathogens Escherichia coli and Listeria monocytogenes, was performed in 96 well plates. A metabolic and clonogenic dependence was established for fluorescent kinetic signals.