High-polyphenol extracts from Sorghum bicolor attenuate replication of Legionella pneumophila within RAW 264.7 macrophages

Authors: GILCHRIST, AUBREY - Kansas State University; Smolensky, Dmitriy; Cox, Sarah; PERUMAL, RAMASAMY - Kansas State University; Noronha, Leela; SHAMES, STEPHANIE - Kansas State University

Submitted to: FEMS Microbiology Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/18/2020
Publication Date: 3/19/2020
Citation: Gilchrist, A., Smolensky, D., Cox, S.R., Perumal, R., Noronha, L.E., Shames, S. 2020. High-polyphenol extracts from Sorghum bicolor attenuate replication of Legionella pneumophila within RAW 264.7 macrophages. FEMS Microbiology Letters. https://doi.org/10.1093/femsle/fnaa053.
DOI: https://doi.org/10.1093/femsle/fnaa053

Interpretive Summary: Plant polyphenols have been previously shown to exhibit antimicrobial activity. While sorghum is a diverse crop with some varieties having high amount of polyphenols, the antimicrobial affects of sorghum polyphenols have not been studied. In this project, the authors looked at the efficacy of sorghum polyphenols on the bacteria which causes Legionare's disease in immune compromised individuals. The results have shown that sorghum polyphenols speed the clearance of the bacteria in mouse macrophage cell line. The polyphenols exhibited no toxicity to the mouse macrophages or to the bacteria growing outside of the macrophages. Normally the clearance of the bacteria is facilitated by an innate immune system protein Tumor Necrosis Factor (TNF). When the cells were treated with sorghum polyphenols, the clearance of the bacteria was enhanced with and without the presence of TNF, indicating that sorghum polyphenols may enhance clearance of the bacteria through novel mechanisms. This information will promote further study of sorghum polyphenols as antimicrobial agents.

Technical Abstract: Polyphenols derived from a variety of plants have demonstrated antimicrobial activity against diverse microbial pathogens. Legionella pneumophila is an intracellular bacterial pathogen that opportunistically causes a pulmonary disease in humans, called Legionnaires’ Disease, via replication within macrophages. Previous studies demonstrated that tea polyphenols attenuate L. pneumophila intracellular replication within mouse macrophages via amplification of tumor necrosis factor (TNF) production. Sorghum bicolor is a sustainable and resilient crop that thrives in arid environments and is well suited to continued production in warming climates. Polyphenols derived from sorghum have anticancer and antioxidant properties, but their antimicrobial activity has not been evaluated. Here, we investigated the impact of sorghum polyphenols on L. pneumophila intracellular replication within RAW 264.7 mouse macrophages. We discovered that sorghum high-polyphenol extract (HPE) treatment attenuates L. pneumophila intracellular replication in a dose dependent manner. Sorghum HPE did not impair bacterial replication in vitro or impact macrophage viability. Moreover, in contrast to tea polyphenols, HPE treatment impaired TNF secretion from infected macrophages. Thus, polyphenols derived from sorghum enhance macrophage restriction of L. pneumophila by a novel mechanism. This work provides a foundation for use of sorghum as an antimicrobial agent.