Synergistic inactivation of Pseudomonas aeruginosa by oregano oil and blue light

摘要

Background and Objectives: Antimicrobial resistance is a rapidly evolving and emerging threat to modernmedicine. Non-antibiotic approaches can be alternatives to minimize the development of antimicrobialresistance. The present study aims at investigation of synergistic effects of antimicrobial blue light (aBL) at405 nm with oregano oil on bacterial inactivation, both of which are non-antibiotic approaches and possessdifferent and multiple targets.Materials and Methods: The bactericidal efficacy of aBL and/or oregano oil against Pseudomonas aeruginosa01 (PA01) was evaluated in in vitro and in infected mouse burns.Results: A combination of aBL at 405 nm with oregano oil synergistically enhanced the efficacy of PA01inactivation in vitro. When aBL at 180 J/cm~2 or 150 J/cm~2 was combined with oregano oil at 0.3 or 0.4 mg/mL,respectively, approximately 8-log_(10) CFU reduction was achieved. In contrast, aBL alone reduced only about 2-log_(10) CFU, whereas oregano oil alone at ≤ 0.8 mg/ml did not kill the bacterium significantly under similarconditions. In vivo animal study showed that aBL at 270 J/cm~2 in combination with oregano oil at 2 mg/mldiminished the bacterial bioluminescence by approximately 8-log_(10) if applied 16 h after bacterial inoculationonto the infected mouse burns. In marked contrast, aBL or oregano oil alone decreased the bacterialbioluminescence by approximately 2.7- or 1.5-log_(10), respectively. Moreover, we identified twenty differentcomponents that account for 97.45% of the total oil composition by gas chromatography-mass spectrometry(GC/MS). The major components are carvacrol (72.25%) and thymol (6.62%) and their synergy with aBL arebeing tested individually.Conclusion: A combination of aBL with oregano oil can be a potential alternative for effective treatment ofbacterial infections locally.