Oregano Oil and Harmless Blue Light to Synergistically Inactivate Multidrug-Resistant Pseudomonas aeruginosa

Abstract

Blue light (BL) at 405 nm and oregano essential oil (OEO) have shown bactericidal activity by its own. Here, we demonstrated that the two synergistically killed multidrug-resistant (MDR) Pseudomonas aeruginosa (Pa). Pa ATCC19660 and HS0065 planktonic cells and mature biofilms were reduced by more than 7 log10 after treatment by BL combined with OEO, in sharp contrast to no significant bacterial reduction with the monotreatment. The duo also sufficiently eliminated acute or biofilm-associated infection of open burn wounds in murine without incurring any harmful events in the skin. The synergic bactericide was attributed mainly to the ability of OEO to magnify cytotoxic reactive oxygen species (ROS) production initiated by BL that excited endogenous tetrapyrrole macrocycles in bacteria while completely sparing the surrounding tissues from the phototoxic action. OEO ingredient analysis in combination with microbial assays identified carvacrol and its isomer thymol to be the major phytochemicals that cooperated with BL executing synergic killing. The finding argues persuasively for valuable references of carvacrol and thymol in assessing and standardizing the bactericidal potential of various OEO products.

Antibacterial and Antibiofilm Effects of Different Samples of Five Commercially Available Essential Oils

“…Their inhibitory activity against all bacteria tested is similar to Amoxicillin-Clavulanic acid. Our results were similar to those obtained in other studies, which confirm both activities (antibacterial and antibiofilm) on S. aureus [80], E. coli [81], and P. aeruginosa [82,83].…”

Photochemical Strategies toward Precision Targeting against Multidrug-Resistant Bacterial Infections

“…27 Blue light as an efficient bactericidal means is supported by wealth of literature regardless of drug resistance. 50,51 Therefore, blue light, as opposed to UV light, is recommended to be applied in phenolic compound-based POT. Besides, phenolic compounds, which are extracted from natural compounds, exhibit better biocompatibility and bioavailability compared to synthetic pharmaceuticals.…”

“…It would be more rational to apply UV light for food decontamination, not for clinics. ,, On the contrary, blue light is highly biocompatible and holds great potential for clinical practices . Blue light as an efficient bactericidal means is supported by wealth of literature regardless of drug resistance. , Therefore, blue light, as opposed to UV light, is recommended to be applied in phenolic compound-based POT.…”

Inhibitory effect of natural compounds on quorum sensing system in Pseudomonas aeruginosa: a helpful promise for managing biofilm community

“…An examination of the ingredients of oregano EO, together with microbiological tests, revealed that carvacrol and its isomer thymol are the primary phytochemicals that work together with BL to achieve synergistic killing. This research provides compelling evidence for the use of carvacrol and thymol as helpful benchmarks in evaluating and establishing the antibacterial effectiveness of different oregano EO products ( Lu et al, 2022a ). Therefore, as mentioned, in addition to the use of a thymol-based drug platform, the combined use of BL and thymol could be a promising antibiofilm approach for managing P. aeruginosa infections; however, more confirmatory studies are needed in this field.…”