Antimicrobial resistance is a concern to public health, with methicillin resistant Staphylococcus aureus (MRSA) being particularly important. Blue light at 405 nm has demonstrated efficacy for the treatment of localized infections. With respect to MRSA, aBL is not effective enough to be developed into a stand-alone therapy. Findings demonstrated the antioxidant properties of the S. aureus pigment, staphyloxanthin (STX). We hypothesized that the efficacy of 405 nm light on MRSA may improve with STX photolysis using 460 nm light. We report an approach that exploits the STX photolysis effect of 460 nm light to sensitize MRSA to 405 nm light.
Otopathogens such as Moraxella Catarrhalis and Haemophilus influenzae are the major causes of pediatric chronic and recurrent otitis media (OM). This pilot study showed that both M. catarrhalis and H. influenzae were highly susceptible to antimicrobial blue light (aBL) inactivation at 405 nm, either in suspensions and biofilms. Transmission electron microscopy showed aBL-induced damage of cell membrane in M. catarrhalis cells. Ultra-performance liquid chromatography results revealed that protoporphyrin IX and coproporphyrin are the most abundant species of endogenous porphyrins in M. catarrhalis. Our findings suggest that aBL is potentially an effective alternative antimicrobial therapy for OM.
KEYWORDS: In vivo imaging, Skin, In vitro testing, Raman spectroscopy, Tissues, Bacteria, Pathogens, Scanning electron microscopy, Laser therapeutics, Resistance
With the effectiveness of antimicrobials waning because of antimicrobial resistance, it is imperative that novel strategies are investigated for the treatment of infections. Antimicrobial blue light (aBL) is an innovative strategy that has proven efficacy against an array of pathogens, albeit, with different species having variable susceptibilities to the therapy. Quinine was discovered during the mid-17th century as a plant-derived potent antimalarial. More recently, its bactericidal properties were revealed, illustrating its potential as an antimicrobial adjuvant. Here we report a novel combination therapy, aBL+quinine hydrochloride (Q-HCL) for the treatment of multi-drug resistant infections. QHCL successfully potentiated the antimicrobial effects of aBL in numerous microbial pathogens of different etiologies, in vitro and in vivo. In addition, it synergistically improved the antimicrobial effects of aBL against bacterial biofilms. Raman spectroscopy revealed that concurrent exposure of aBL and Q-HCL improved uptake of Q-HCL into bacterial cells, when compared to the non aBL exposed sample. In addition, ultra-pure liquid chromatography (UPLC) revealed that Q-HCL increased the relative abundance of porphyrins in bacteria, suggesting the mechanism of this synergistic interaction is through increased production of intermediate photosensitizing porphyrins arising through perturbation of the heme biosynthesis pathway by Q-HCL. Genotoxic potential of the combination therapy against mouse skin tissue, was evaluated using the TUNEL assay, where it was revealed that a high dose exposure of aBL+Q-HCL (<3x the therapeutic dose) was not genotoxic to mouse skin tissue. In conclusion, the findings strongly suggest the potential of aBL+Q-HCL combination therapy as an alternative to traditional antibiotics for the treatment of localized infections.
Antimicrobial resistance in Neisseria gonorrhoeae is a major issue of public health, and there is a critical need for the development of new anti-gonococcal strategies. In this study, we investigated the effectiveness of antimicrobial blue light (aBL; 405 nm wavelength), an innovative non-pharmacological approach, for the inactivation of N. gonorrhoeae. Our findings indicated that aBL preferentially inactivated N. gonorrhoeae, including antibiotic-resistant strains, over human vaginal epithelial cells in vitro. Furthermore, no genotoxicity of aBL to the vaginal epithelial cells was observed at the radiant exposure for inactivating N. gonorrhoeae. aBL also effectively inactivated N. gonorrhoeae that had attached to and invaded into the vaginal epithelial cells in their co-cultures. No gonococcal resistance to aBL developed after 15 successive cycles of sub-therapeutic aBL inactivation. Taken together, aBL represents a potent potential treatment for antibiotic-resistant gonococcal infection.
With the increasing number of pathogenic microbes that are becoming resistant to routinely used antimicrobials, it is important to look to non-traditional approaches for the treatment of infections. Antimicrobial blue light (aBL;405 nm) is a novel strategy for the treatment of infections. Here we report an investigation into the potential for resistance development to aBL in three clinically important Gram-negative bacteria, through sequential exposure in vitro and in vivo. We found that 20 cycles of aBL exposure, in vitro, did not incur resistance development, in any of the species tested (Acinetobacter baumanii, Pseudomonas aeruginosaor Escherichia coli). In addition, sub-curative sequential aBL treatment of a wound infected with a bioluminescent variant of the P. aeruginosa PAO1 strain, did not influence sensitivity to aBL. In conclusion, it is unlikely that sequential treatment of aBL will result in resistance generation, suggesting that multiple treatments of aBL may be administered without resistance development becoming a concern.
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