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.
Highlights
The use of antibiotics to destroy selectively microorganisms (MO) represents one of the most revolutionary progresses made in scientific medicine, resulting in the treatment and sometimes complete eradication of earlier incurable diseases [1,2]
The bacterial strains used in this work were a recombinant bioluminescent strain of E. coli described in a previous work [12] and the bioluminescent marine bacterium Vibrio fischeri ATCC
Knowing that the light emission in these bacteria is directly proportional to their metabolic activity [12], we used their bioluminescence ability to evaluate their recovery after photodynamic treatment
Summary
The use of antibiotics to destroy selectively microorganisms (MO) represents one of the most revolutionary progresses made in scientific medicine, resulting in the treatment and sometimes complete eradication of earlier incurable diseases [1,2]. Bacteria have developed resistance mechanisms against antimicrobial drugs which were previously highly effective. Bacteria replicate very rapidly and a mutation that helps a MO to survive in the presence of an antibiotic will quickly become predominant in the microbial population [1,3]. Due to resistance to all β-lactam antibiotics, the glycopeptide antibiotic vancomycin has remained as last line of defense against Gram-positive bacteria. Methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci are species that are causing much concern at present [4] and there is an urgent need for the development of novel, convenient, non-resistant and inexpensive measures for fighting microbial diseases [1,5,6]
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