In vitro macrophage activation by edible mushroom extracts varies considerably and is highly correlated to bacterial LPS content

We have previously reported that over 97% of in vitro monocyte/macrophage activation by botanical plant extracts was due to bacterial components (LPS and Braun type lipoproteins). Furthermore, we have also shown that in Echinacea purpurea total bacterial load was significantly correlated with macrophage activity and LPS content. The objective of this study was to evaluate whether the immune enhancing activity also correlate with content of LPS and total bacterial load within edible mushrooms. In experiments using RAW 264.7 macrophages we observed substantial variation (over 1000-fold) in TNF-alpha production exhibited by extracts from 13 different types of mushrooms. Total bacterial load within the mushrooms ranged from 2.2 × 10⁵ to 7.3 × 10⁷ cells/g of dry material and community composition determined by 16S rRNA gene pyrosequencing showed that Pseudomonas was the most abundant genera detected in the majority of the samples. In agreement with our previous research on plant material, there was a strong correlation between macrophage stimulating activity and content of bacterial LPS within mushroom extracts R²= 0.78, p < 0.0001. Differences in total bacterial load within the mushroom material were significantly correlated with macrophage activation R²= 0.32, p < 0.0001 and bacterial LPS content R²= 0.21, p = 0.0004.

This research was partly funded by a grant from the NCCAM and ODS (R01AT007042). Additional funding was also provided by the USDA, ARS Specific Cooperative Agreement No. 58 – 6408 – 1-603.