The inhibitory effect of polyphenols on human gut microbiota

The intestinal microbiota (IM) is responsible for metabolism of many compounds provided in the diet, such as polyphenols, increasing their bioavailability. However, there are remarkably few studies investigating the influence of polyphenols on the composition and activity of the gut microbial community. This study evaluated the influence of the polyphenols naringenin (N), naringin (NR), hesperetin (H), hesperidin (HR), quercetin (Q), rutin (QR), and catechin (CAT) on the growth of human IM representatives (Bacteroides galacturonicus, Lactobacillus sp., Enterococcus caccae, Bifidobacterium catenulatum, Ruminococcus gauvreauii, Escherichia coli). Polyphenols were added to liquid medium at a final concentration of 20, 100 or 250 μg/ml (for Q concentrations were 4, 20 or 50 μg/ml) and their impact on the IM was assessed by measurement of the turbidity after 24-h culture. The minimal inhibitory concentration (MIC) for polyphenols that inhibited bacteria was estimated. CAT had no impact on the tested IM. Q had the strongest impact on R. gauvreauii, B. galacturonicus and Lactobacillus sp. (MIC 20-50 μg/ml) growth, whilst its rutinoside had no impact. NR and HR had no impact, but their aglycones N and H inhibited growth of almost all analyzed bacteria (MIC ≥250 μg/ml). We conclude that flavonoid aglycones, but not their glycosides, may inhibit growth of some intestinal bacteria. This means that polyphenols probably can modulate the IM and indirectly interfere with their own bioavailability.