Antimicrobial Photodynamic Therapy: Study of Bacterial Recovery Viability and Potential Development of Resistance after Treatment

Abstract

Antimicrobial photodynamic therapy (aPDT) has emerged in the clinical field as a potential alternative to antibiotics to treat microbial infections. No cases of microbial viability recovery or any resistance mechanisms against it are yet known. 5,10,15-tris(1-Methylpyridinium-4-yl)-20-(pentafluorophenyl)-porphyrin triiodide (Tri-Py+-Me-PF) was used as photosensitizer. Vibrio fischeri and recombinant Escherichia coli were the studied bacteria. To determine the bacterial recovery after treatment, Tri-Py+-Me-PF (5.0 μM) was added to bacterial suspensions and the samples were irradiated with white light (40 W m−2) for 270 minutes. Then, the samples were protected from light, aliquots collected at different intervals and the bioluminescence measured. To assess the development of resistance after treatment, bacterial suspensions were exposed to white light (25 minutes), in presence of 5.0 μM of Tri-Py+-Me-PF (99.99% of inactivation) and plated. After the first irradiation period, surviving colonies were collected from the plate and resuspended in PBS. Then, an identical protocol was used and repeated ten times for each bacterium. The results suggest that aPDT using Tri-Py+-Me-PF represents a promising approach to efficiently destroy bacteria since after a single treatment these microorganisms do not recover their viability and after ten generations of partially photosensitized cells neither of the bacteria develop resistance to the photodynamic process.

Porphyrin-based cationic amphiphilic photosensitisers as potential anticancer, antimicrobial and immunosuppressive agents

“…specifically against cell-wall, virus polymerase or protease) has inevitably led to the emergence of resistant clones, thus becoming a global threat (Bacon et al 2003;Coen and Whitley 2011;Cortez et al 2011;Memoli et al 2011). Due to ROS-mediated targeting of microbial membranes, membrane proteins, DNA, etc., of various pathogens, PACT represents a broad-spectrum multitargeted approach with very limited, if any, chances for the development of resistant bacteria or viruses (Jori et al 2006, Tavares et al 2010Costa et al 2012b;Dosselli et al 2012;Maisch 2015). PACT has been applied successfully to inactivate bacteria, fungi, protozoans and parasites, especially in topical applications such as skin wounds (burns and diabetic foot ulcers) or oral infections (periodontitis and root canal infections) (Tim 2015).…”

“…Photodynamic antimicrobial chemotherapy (PACT) is a possible remedy as it proved to be effective against methicillinresistant Staphylococcus aureus (MRSA) and other multiresistant bacteria (Maisch 2015). Moreover, there is no evidence for the development of resistance to PACT, and such resistance is considered highly improbable, because the oxidative stress in PACT is initiated by a PS that is usually present at multiple cellular sites (Tavares et al 2010;Maisch 2015). Similarly, PDT attacks tumours by causing oxidative damage to different cellular components, and even though there are some examples of resistance to PDT, evidence of resensitisation and synergy in chemoresistant tumour cell lines support the notion that PDT could play an important role in overcoming cancer drug resistance (Spring et al 2015).…”

Microbicidal Activity of Artificially Generated Hydroxyl Radicals

“…Without irradiation, photosensitizer does not exert cytotoxic effect, indicating that residual toxicity after the treatment is negligible. Furthermore, it is suggested that the PDT does not induce bacterial resistance because singlet oxygen oxidize bacterial cell components non-selectively [26,27]. This is a major advantage in comparison with antibiotics.…”

Evaluation of meso-substituted cationic corroles as potential antibacterial agents

“…These ROS will react with many cellular components that will induce oxidative processes leading to cell death (Bonnett 2000, Maisch 2009, Ergaieg et al 2008, Tavares et al 2011, Costa et al 2013, Wainwright et al 2017. The great advantage of this methodology is the unlikelihood of the microorganisms to develop resistance mechanisms since there is not a particular target in the cell and also the PS don't have to accumulate in its interior to be efficient (Dahl et al 1989, Tavares et al 2010, Costa et al 2011a, Preuß et al 2013, Alves et al 2014a.…”

“…The light output from these bioluminescent bacteria is a highly sensitive marker of their metabolic activity and it can be easily read in a luminometer with a strong correlation between bioluminescence (measured in relative light units, RLU) and viable cell counts. (Tavares et al 2010, Alves et al 2011a, b, Mesquita et al 2014b. The efficiency of the At 20 µM, corroles 2b and 3b were able to reduce A. fischeri bioluminescence of > 6 log 10 RLU after 30 min of irradiation (0.18 kJ cm -2 ) and the results were not significantly different from the pattern of Tetra-Py + -Me (data not shown).…”