Antimicrobial resistance is significant concern to public health that negatively impacts the worldwide populace. With the increasing incidences of multidrug-resistant (MDR) pathogens, treatment of infections is becoming more difficult than ever before. In recent years, our team has been involved with the use of blue light (BL) for the treatment of infection. BL is a potent microbicide that can kill a multiplicity of pathogenic microbes. A concern, however, is that the effects of BL are short lived, when the light switches off, so do the antimicrobial effects.Therefore, we considered, that we could increase the longevity of microbicidal activity of BL via its concomitant application with antibiotics. In this study, we tested our hypothesis that aBL can enhance antibiotic activity in MDR bacteria.
This study investigated the aBL effects on bacterial species carrying β-lactamase genes and alterations in β-lactamase activity following aBL. In addition, we assessed the β-lactamase and protein damage induced by aBL and the bactericidal effect of aBL combined with a β-lactam antibiotic. Our finds demonstrate that aBL can effectively kill strains carrying β-lactamase genes and reduce the β-lactamase activity. We also demonstrated the role of porphyrins on the photoreaction promoted by aBL and the resulting protein damage. Additionally, ceftazidime activity was significantly improved by aBL in a Metallo-β-lactamase strain. Our finds support the aBL against the β-lactamases and encourage future outcomes.
Antimicrobial resistance has necessitated the investigation of novel approaches to prolong the use of conventional antibiotics. We hypothesized that using the innovative ‘drug-free’ approach, antimicrobial blue light (aBL), which is a selective generator of ROS in bacteria, we can exploit increases in intracellular ROS to synergize to conventional antibiotics, given that they share a parallel pathway of bactericidal activity. Studies from our group have also suggested the adjuvant potential of aBL that may further promote the effectiveness of antibiotics. Here, we explored the synergistic and adjuvant effects of aBL using different antibiotic classes against bacteria, in vitro and in vivo.
In this study, we first evaluated the effectiveness of antimicrobial blue light (aBL) in vitro against Vibrio vulnificus in planktonic and biofilm cultures. In addition, we assessed aBL for the prevention of potentially lethal burn infections caused by Vibrio vulnificus in mice. We found that aBL was highly effective in killing V. vulnificus in both planktonic and biofilm cultures. Moreover, aBL significantly reduced the bacterial burden in infected mouse burns and reduced the rate of fatal sepsis in mice.
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.
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.
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.
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