Bacterial components are the major contributors to the macrophage stimulating activity exhibited by extracts of common edible mushrooms

Authors: TYLER, HEATHER - University Of Mississippi; HARON, MONA - University Of Mississippi; PUGH, NIRMAL - University Of Mississippi; ZHANG, JIN - University Of Mississippi; JACKSON, COLIN - University Of Mississippi; PASCO, DAVID - University Of Mississippi

Submitted to: Food & Function
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/2016
Publication Date: 9/15/2016
Citation: Tyler, H.L., Haron, M.H., Pugh, N.D., Zhang, J., Jackson, C.R., Pasco, D.S. 2016. Bacterial components are the major contributors to the macrophage stimulating activity exhibited by extracts of common edible mushrooms. Food & Function. 7:4213-4221.

Interpretive Summary: A growing body of evidence supports the theory that bacterial communities within immune-enhancing botanicals are the principal source of components responsible for the activation of innate immune cells exhibited by extracts from these plants. Since mushrooms have a long history of medicinal use for enhancing immune function, the objective of the current study was to determine if bacterial products derived from the bacteria that colonize these fungi are major contributors to the innate immune enhancing activity exhibited by these products. Statistically significant correlations were observed between in vitro macrophage activation exhibited by mushroom extracts and lipopolysaccharide content and bacterial load of these samples. Analysis of the bacterial community associated with the mushroom samples demonstrated that the composition was frequently dominated by Pseudomonas. These results suggest that components derived from mushroom associated bacteria contribute substantially to the innate immune enhancing activity exhibited by mushrooms and may result in similar therapeutic actions as reported for ingestion of bacterial preparations such as probiotics.

Technical Abstract: Background: Recent studies have indicated that a major contributor to the innate immune enhancing properties of some medicinal plants derive from the cell wall components of bacteria colonizing these plants. Purpose: The purpose of the current study was to assess if the bacteria present within edible and medicinal mushrooms substantially contribute to innate immune stimulating potential of these mushrooms. Study Design: Whole mushrooms from thirteen types of edible fungi and individual parts from Agaricus bisporus were analyzed for in vitro macrophage activation as well as bacterial lipopolysaccharides (LPS) content,cell load, and community composition. Methods: In vitro macrophage activation was measured as TNF-alpha production by RAW 264.7 cells exposed to mushroom extracts. Bacterial cell load and community composition were determined by extracting deoxyribonucleic acid (DNA) from mushrooms and analyzing the 16S ribosomal ribonucleic acid (rRNA) gene. Results: Substantial variation between samples was observed in macrophage activation (over 500-fold), total bacterial load (over 200-fold), and LPS content (over 10 million-fold). Both LPS content (p=0.832, p <0.0001) and total bacterial load (p=O.701, p <0.0001) correlated significantly with macrophage activation in the whole mushroom extracts. 16S rRNA gene sequencing demonstrated the bacterial community within whole mushroom samples was frequently dominated by Pseudomonas. Significant correlations between macrophage activation and total bacterial load (p= 0.723, p=0.0001) and LPS content (p=0.951, p<0.0001)were also observed between different tissues of Agaricus bisporus. In the different tissue parts Pseudomonas and Flavobacterium were the most prevalent genera identified and these taxa were significantly correlated with in vitro macrophage activation (p=0.697, p<0.0001and p=0.659, p=0.0001, respectively). Conclusion: These results suggest that components derived from mushroom associated bacteria contribute substantially to the innate immune enhancing activity exhibited by mushrooms and may result in similar therapeutic actions as reported for ingestion of bacterial preparations such as probiotics.