Inhibition of Bacteroidetes and Firmicutes by select phytochemicals

Authors: LAKES, JOURDAN - University Of Kentucky; RICHARDS, CHRISTOPHER - University Of Kentucky; Flythe, Michael

Submitted to: Anaerobe
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/23/2019
Publication Date: 12/24/2019
Citation: Lakes, J.E., Richards, C.I., Flythe, M.D. 2019. Inhibition of Bacteroidetes and Firmicutes by select phytochemicals. Anaerobe. 61:102145. https://doi.org/10.1016/j.anaerobe.2019.102145.
DOI: https://doi.org/10.1016/j.anaerobe.2019.102145

Interpretive Summary: It is now recognized that the bacteria and other microorganisms in the gut influence many aspects of human and animal health. In addition to altering digestion in ruminants, other animals and humans, microbe-host interactions can alter host metabolic conditions, such as obesity and inflammation. It has long been understood that diet dramatically affects gut microorganisms in ruminants, and this is proving to be true in non-ruminants as well. However, phytochemicals, or plant secondary metabolites, are usually present in low concentrations. It is not always clear how minor dietary components, like phytochemicals, impact gut bacteria. Here we propose that phytochemicals can impact gut bacteria through antimicrobial action. Four well known bacteria were selected for study. 1 )Acetoanaerobium (Clostridium) sticklandii is from ruminants. 2) Clostridioides difficile (commonly called "C. diff") is a human pathogen that is closely related to A. sticklandii. 3)Prevotell bryantii is from ruminants. 4) Bacteroides fragilis, of human origin, is a relative of P. bryantii. The bacteria were grown in the presence of each of six common phytochemicals over a range of concentrations. The phytochemicals included five common alkaloids (nitrogen-containing phytochemical): berberine, capsaicin, nicotine, piperine and quinine, as well as the polyphenol (no nitrogen), curcumin. All of the phytochemicals inhibited at least one species of bacteria at some concentration. In general, quinine and berberine were the strongest antimicrobials and piperine the weakest. The conclusion is that commonly ingested phytochemicals can influence gut bacteria through antimicrobial mechanisms of action. The impact of this research is that it should be considered that ingested phytochemicals can influence the composition of gut microorganisms through antimicrobial activity.

Technical Abstract: Current research indicates that changes in gut microbiota can impact the host, but it is not always clear how dietary and environmental factors alter gut microbiota. One potential factor is antimicrobial activity of compounds ingested by the host. The goal of this study was to determine the antimicrobial activity of common plant secondary metabolites against pure cultures of paired, structurally and phylogenetically distinct gastrointestinal bacteria of human or bovine origin: Prevotella bryantii B14, Bacteroides fragilis 25285, Acetoanaerobium (Clostridium) sticklandii SR and Clostridioides difficile 9689. When growth media were amended with individual phytochemicals (the alkaloids: berberine, capsaicin, nicotine, piperine and quinine and the phenolic: curcumin), growth of each species was inhibited to varying degrees at the three greatest concentrations tested (0.10 to 10.00 mg mL-1). The viable cell numbers of all the cultures were reduced, =4-logs, by berberine at concentrations =1.00 mg mL-1. Quinine performed similarly to berberine for B14, 25285, and SR at the same concentrations. The other phytochemicals were inhibitory, but not as much as quinine or berberine. Nicotine had activity against all four species (=2-log reduction in viable cell number at 10.00 mg mL-1), but had stronger activity against the Gram-positive bacteria, SR and 9689, (=4-log reductions at 10.00 mg mL-1). In conclusion, the phytochemicals had varying spectra of antimicrobial activity. These results are consistent with the hypothesis that ingested phytochemicals have the ability to differentially impact gut microbiota through antimicrobial activity.