Activities and Prevalence of Proteobacteria Members Colonizing Echinacea purpurea Fully Account for Macrophage Activation Exhibited by Extracts of This Botanical

Our previous work identified a fraction from Echinacea that potently activated macrophages in vitro through a Toll-like receptor 2-dependent mechanism. The active component was later identified as bacterial Braun-type lipoproteins. This agent together with bacterial LPS were responsible for over 97% of the macrophage activation potential exhibited by extracts of Echinacea and other immune enhancing botanicals. Subsequent studies indicated that ˜50% of the variation in in vitro macrophage stimulating activity exhibited by E. purpurea extracts could be accounted for by differences in total bacterial load within the plant material. We then tested the hypothesis that the type of bacteria, in addition to bacterial load, was necessary to fully account for extract activity. Bacterial community composition within commercial and freshly harvested (wild and cultivated) E. purpurea aerial samples was determined using high-throughput 16S rRNA gene pyrosequencing. Bacterial isolates representing 38 different taxa identified to be present within E. purpurea were acquired, and the activity exhibited by the extracts of these isolates varied by over 8,000-fold. Members of the Proteobacteria exhibited the highest potency for in vitro macrophage activation and were the most predominant taxa. Furthermore, the mean activity exhibited by the Echinacea extracts could be solely accounted for by the activities and prevalence of Proteobacteria members comprising the plant-associated bacterial community. The efficacy of E. purpurea material to treat respiratory infections may be partially determined by the Proteobacterial community composition of this plant, since ingestion of bacteria (probiotics) and other extracts containing bacterial components is reported to have a protective effect against this health condition.