The Antibacterial Activitiy Of Unifloral Honey From Scrophularia Ningpoensis Hemsl.and The Associated Mechanism

In recent years,discovering antimicrobial substances from natural products has attracted extensive attention due to the stagnant development of antibiotics and the persistent expansion of drug resistance.Honey,possessing profound antibacterial activity,has been used as a remedy for skin wounds infection and gastrointestinal disease for thousands of years.However,the in vitro and in vivo antibacterial activity and the associated mechanism of honey from medicinal plants are still unknown.In this study,eight kinds of uniflorous honey derived from medicinal plants native to China was screened for the antimicrobial activity.We investigated the in vitro and in vivo effectiveness and mechanisms of antibacterial action between Scrophularia ningpoensis Hemsl.honey（S.ningpoensis honey）and manuka honey in depth,and explored the relationship between the components and antibacterial activity of S.ningpoensis honey through non-targeted metabolomics.1.Eight kinds of medicinal plant-derived uniflorous honey native to China were gathered.Their in vitro antibacterial activities were evaluated using seven strains of Gram-positive/negative bacteria in comparison with manuka honey.It was found that S.ningpoensis honey possessed the strongest in vitro antibacterial efficacy comparable to manuka honey among the eight tested unifloral honey samples.2.When exploring the antibacterial mechanism of S.ningpoensis honey,it was found that it could induce bacterial death through disrupting cell membrane and genomic DNA,and such an ability was stronger than manuka honey.Meanwhile,S.ningpoensis honey could down-regulate the expression of genes associated with virulence,biofilm formation and invasion of bacteria,including ica A,ica D,eno,sar A,agr A,sig B,fib and ebps in S.aureus,and las I,las R,rhl I,rhl R and alg C in P.aeruginosa.3.In the in vivo assays,S.ningpoensis honey did not exhibit obvious antibacterial activity in the systemically infected mouse model,while it significantly reduced the bacterial load of the muscles under the acute MRSA-infected skin wounds.At the same time,S.ningpoensis honey significantly decreased the level of TNF-αin the sera of S.aureus and P.aeruginosa-infected mice,and the level of alanine transaminase,aspartate aminotransferase,and alkaline phosphatase in the sera of healthy mice.4.The untargeted metabolomic technique was employed to reveal the differential compounds present in S.ningpoensis honey and manuka honey.A total of 249 differential metabolites were identified,with 100upregulated and 149 down-regulated in S.ningpoensis honey vs.manuka honey.It was found that apart from H₂O₂,some other nonperoxide compounds such as adenosine,chavicol,4-methylcatechol,trehalose,palmitoleic acid and salidroside,might play a vital role in the antibacterial properties of S.ningpoensis honey.This study is the first to thoroughly investigate the in vitro and in vivo antibacterial activity and mechanisms of monofloral honey from medicinal plants native to China and the componential profile of S.ningpoensis honey.It facilitates the application of medicinal plant-derived honey in place of manuka honey.Meanwhile,it offers the clues towards the discovery of antibacterial substances from medicinal plant-derived honey and exploring novel target sites in bacteria.