Investigation of antimicrobials from native British plants used in 10th century Anglo-Saxon wound healing formulations

Chinese and Indian cultures consider their ancient herbal texts valuable resources in the search for novel compounds with potential pharmacological applications. However, despite a rich history of medicinal plant use throughout the British Isles, much of the native flora recorded in the Anglo-Saxon medical texts (the Herbarium, Bald’s Leechbook and the Lacnunga) studied here has yet to be evaluated. A model was developed for bio-screening medicinal plants using <30 g of dried material for bioassay and structure elucidation. In this study, six native species were screened using a 96-well microdilution bioassay (200, 40 and 8 μg/mL) against representative strains of Gram-positive and Gram-negative pathogens commonly found in wounds. All plants exhibited activity against Gram-positive organisms in one or more leaf extracts (MIC50 200 μg/mL). Of the 8 extracts per plant, the 25% and 75% EtOH root extracts of Agrimonia eupatoria L. and Potentilla reptans L. were effective against S. aureus at the lower concentration (MIC50 8 μg/mL) and inhibited growth of Gram-negative pathogen E. coli (MIC50 40 μg/mL). P. reptans was selected for further investigation on the basis of its activity against E. coli and underreported phytochemistry compared to A. eupatoria. In the MIC assay the 75% EtOH root extract of P. reptans demonstrated the widest range of activity against S. aureus (MIC50 31.25 – full MIC of 1000 μg/mL). The P. reptans root decoction was the most potent extract against E. coli (MIC50 3.9 μg/mL) and comparable to chloramphenicol, a broad spectrum antibiotic. Principal components analysis (PCA) when overlaid with antimicrobial activity, directed the optimisation of the HPLC and LC-MS methods. Seven antimicrobial compounds were putatively identified for P. reptans (agrimonolide-6-O-glucopyranoside, chlorogenic acid, ellagic acid, epicatechin, procyanidin B, procyanidin C, and tormentic acid). This study has shown some native species in the Anglo-Saxon formulations may have been effective for treating bacterial infection in wounds and that the medical texts are a valuable source for rediscovering plants and medicinal uses lost to Western herbal practice.