Understanding the antimicrobial properties of natural plant extracts and herbal infusions

Herbs, teas and natural products have long been used in traditional Chinese and Indian medicines and are becoming increasingly popular for selfcare, and for use in modern clinical practice. The 2018 NICE and PHE guidelines for coughs states that antibiotics should not be a first line treatment, and that honey and several herbs (such as Pelargonium) were recommended. There is a need to consider efficacy on complex polymicrobial communities (e.g. biofilms), which are known to be responsible for most chronic infections. Pilot data has also shown that a green tea-based infusion (Camellia sinsensis) and a turmeric infusion (Curcuma longa) demonstrates anti-viral activity when tested against coronavirus. Many other herbs and natural products have antimicrobial activity that has been reported but are often based on single species studies and do not reflect realistic conditions. Building on preliminary data from a NBIC-funded pilot study, this project aims to systematically test a range of herbal and plant extracts, and infusions, using standard and advanced methods. Using a range of bacterial and viral pathogens commonly associated with upper respiratory tract infections, including Streptococcus pyrogenes, Pseudomonas aeruginosa, Haemophilus influenzae, Moraxella catarrharis, coronavirus, RSV, and flu, we will test existing, and develop new, models for measuring antimicrobial activity. This will include understanding the mechanisms of action. Aims: Assessment of the antibiofilm activity of a range of extracts on several key bacterial pathogens using MBEC and MBIC assays. Develop a cell culture assay to allow investigation with key viral pathogens on upper respiratory tract cell lines to test the antiviral activity of extracts. Determine any synergistic or antagonistic relationships between extracts linked to antimicrobial activity. Understand the mechanisms of antimicrobial activity using transcriptomics, proteomics and advanced microscopy imaging, as well as tracking the development of viable but nonculturable (VBNC) populations and resistance profiles.