Evaluating Tannins and Flavonoids from Traditionally Used Medicinal Plants with Biofilm Inhibitory Effects against MRGN E. coli

Abstract

In the search for alternative treatment options for infections with multi-resistant germs, traditionally used medicinal plants are currently being examined more intensively. In this study, the antimicrobial and anti-biofilm activities of 14 herbal drugs were investigated. Nine of the tested drugs were traditionally used in Europe for treatment of local infections. For comparison, another five drugs monographed in the European Pharmacopoeia were used. Additionally, the total tannin and flavonoid contents of all tested drugs were analyzed. HPLC fingerprints were recorded to obtain further insights into the components of the extracts. The aim of the study was to identify herbal drugs that might be useable for treatment of infectious diseases, even with multidrug resistant E. coli, and to correlate the antimicrobial activity with the total content of tannins and flavonoids. The agar diffusion test and anti-biofilm assay were used to evaluate the antimicrobial potential of different extracts from the plants. Colorimetric methods (from European Pharmacopeia) were used for determination of total tannins and flavonoids. The direct antimicrobial activity of most of the tested extracts was low to moderate. The anti-biofilm activity was found to be down to 10 µg mL−1 for some extracts. Tannin contents between 2.2% and 10.4% of dry weight and total flavonoid contents between 0.1% and 1.6% were found. Correlation analysis indicates that the antimicrobial and the anti-biofilm activity is significantly (p < 0.05) dependent on tannin content, but not on flavonoid content. The data analysis revealed that tannin-rich herbal drugs inhibit pathogens in different ways. Thus, some of the tested herbal drugs might be useable for local infections with multi-resistant biofilm-forming pathogens. For some of the tested drugs, this is the first report about anti-biofilm activity, as well as total tannin and flavonoid content.

Chemical Profiling and Antioxidant Activity of Tanacetum vulgare L. Wild-Growing in Latvia

“…Considering that ethanol–water is a popular solvent for tannin extraction [ 28 ], the colorimetric tannin detection method from European Pharmacopeia was applied. It has to be taken into account that in this method, the tannin content is normalized to the redox potential of pyrogallol, suggesting that there might exist biases due to different redox potentials of the different tannins (e.g., catechines vs. gallotannins) [ 29 ]. Tannins are classified as hydrolyzable (gallic acid and ellagic acid) and condensed (proanthocyanidins) tannins [ 30 ].…”

“…The analyses of the extracts were carried out in accordance with the monograph 2.8.14 available in the European Pharmacopoeia. In short, according to Neumann 2022 [ 29 ], the drugs were pulverized, and approximately 500 mg was extracted with boiling water (150 mL) for 30 min. The water extract was filtered and split into two parts of equal volume.…”

Cinnamomum sp. and Pelargonium odoratissimum as the Main Contributors to the Antibacterial Activity of the Medicinal Drink Horchata: A Study Based on the Antibacterial and Chemical Analysis of 21 Plants

“…In a recent study by Neumann et al [ 92 ], when exploring the antimicrobial activity of several plant extracts against multidrug-resistant E. coli , they found that the inhibitory activity was mostly related to the tannin concentration rather than flavonoids (especially in alcoholic extracts). This finding is consistent with the presence of tannins in both Cinnamomum sp.…”

Quality parameters for the medicinal plant Drosera rotundifolia L.: A new approach with established techniques

“…This method is based on photometric analysis of a color complex, the color complex being formed by boric acid and oxalic acid. The method was described in detail in the publication by Neumann et al [ 47 ] The second method was a HPLC method which allowed quantification of four main flavonoids (hyperoside, isoquercitrin, quercetin, and 2″‐ O ‐galloylhyperoside). A Shimadzu chromatography system (LC‐20AD, Shimadzu Scientific Instruments, Nakagyo‐ku) with a photodiode array detector (PDA) was used.…”