In vitro and in vivo evaluation of antibacterial activity and mechanism of luteolin from Humulus scandens against Escherichia coli from chicken.

Resistance of Escherichia coli (E.coli) to antibiotics has steadily increased over time; hence, there is an urgent need to develop safer alternatives to antibiotics. The present study aimed to evaluate the effect of luteolin (Lut) on E. coli from chicken. The bioactive compound Lut from Humulus scandens was selected by network pharmacology and molecular docking analyses. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and confocal laser scanning microscopy (CLSM) were used to observe the effects of Lut on the morphology and structure of E. coli cells. The data-independent acquisition (DIA) method was used to analyze protein expression level of E. coli before and after Lut treatment. The in vivo evaluation of the antibacterial, anti-inflammatory, and oxidative effects of Lut on E.coli was conducted using E.coli isolated strains infected the SPF chicken model. The network pharmacology analysis revealed 19 distinctive bioactive compounds such as Lut and β-sitosterol in H. scandens; furthermore, 30 core targets were selected from H. scandens. The KEGG enrichment analysis showed that the PI3K-Akt, TNF, MAPK, IL-17, JAK-STAT, and HIF-1 pathways were related from H. scandens. Based on the results of the network pharmacology analysis, Lut was subjected to screening by molecular docking analysis to determine its antibacterial effect on E. coli and the associated mechanism of action. The minimum inhibitory concentration (MIC) of Lut against E. coli standard strains was 500 µg/mL. SEM, TEM, and CLSM results indicated that Lut damaged the cell wall and cell membrane of E. coli strains and destroyed the cell structure, leading to cell death.The expression level of membrane structure, Phenylalanine metabolism and some other metabolic pathways in E.coli changed after treatment with Lut (P < 0.05). In vivo experiments in the SPF chicken model showed that Lut treatment alleviated the decline in the growth performance of chickens (P < 0.05), prevented pathological changes in the correspond ding organs and suppressed the inflammatory response induced by E. coli infection (P < 0.05), improved the immunity and antioxidant capacity of chickens (P < 0.05), and protected them against infection with E. coli strains. To summarize, Lut from H. scandens can inhibit E. coli growth by damaging the cell membrane structureand affecting the expression level of some metabolic proteins. In vivo experiments also showed that Lut can significantly reduce the damage caused by E. coli isolates on SPF chickens, improve their antioxidant capacity and immunity, and reduce inflammatory responses following E. coli infection.