Long before we had modern antibiotics to rely on, people often turned to traditional medicines from plants to treat infections.
The root of tormentil (Potentilla erecta), a small yellow wildflower that grows across Ireland, the UK and Europe, was used for centuries in Irish and European traditional medicine. It was used to treat wounds, sore throats, diarrhoea and gum disease. These traditional uses suggested that tormentil could contain compounds powerful enough to kill microbes.
Our latest research has now shown that not only does tormentil have antimicrobial activity, it may also be powerful enough to fight microbes that are resistant to modern antibiotics.
Antimicrobial resistance is a growing global threat. This occurs when bacteria evolve to survive the drugs used to treat common infections. This makes some infections very difficult and sometimes impossible to treat. Antimicrobial resistance could be pushing us back to a time when once treatable infections could again become deadly.
Researchers are therefore searching for new antimicrobial compounds. Plants are a promising source, having evolved over millennia to produce a wide range of bioactive chemicals to defend themselves against microbes.
In our recent study, we investigated whether various Irish bogland plants contain compounds that could help fight multi-drug resistant bacteria.
To do this, we prepared extracts from over 70 different plant species collected from bogs across Ireland. We then tested them against clinically relevant bacterial pathogens in the laboratory – including bacteria which cause severe pneumonia and urinary tract infections.
We used antimicrobial susceptibility testing to see whether the extracts inhibited bacterial growth. This involved exposing the bacteria to the various plant extracts to see which extract inhibited the growth of the bacteria.
We then tested these extracts on biofilms to determine whether the plant compounds could prevent bacteria from forming biofilms. Biofilms are bacterial communities surrounded by a slimy carbohydrate shield that protects them from antibiotics, disinfectants and the immune system.
Excitingly, our initial screening showed that tormentil extracts were antimicrobial and limited the formation of biofilms. This suggested these extracts contained compounds with antimicrobial activity, which may explain their historical use to treat infection.
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We also explored whether these plant extracts could work in combination with existing antibiotics, as some plant compounds don’t kill bacteria directly but instead can make antibiotics work better. So we combined low levels of the antibiotic colistin – an antibiotic that is only used as a last-resort against severe infections due to its potential toxicity to patients – with the tormentil extract. The low-level antibiotic dosage wasn’t enough to kill the bacteria when used on its own. But when combined with the tormentil extract, the plant compound enhanced the antibiotic’s efficacy.
Part of our team then performed an analysis to identify the compounds present in the tormentil extracts. Potentilla plants are known to contain naturally occurring compounds, such as ellagic acid and agrimoniin, which have antioxidant and anti-inflammatory properties.
We tested ellagic acid and agrimoniin compounds which were present in our bogland tormentil. We showed that these specific compounds could inhibit bacterial growth. This indicates they may be responsible for tormentil’s antimicrobial activity.
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We subsequently found these compounds were doing this by scavenging iron – a nutrient that’s essential for bacterial growth. This effectively starved the bacterial cells, preventing them from growing. We are now focused on optimising this antimicrobial activity and developing formulations to test its potential as a treatment in experimental models.
Nature has always been a rich source of medicine. Many antibiotics that we use today originally came from natural sources. For instance, the potent, last-resort antibiotics vancomycin – which is used to treat MRSA (methicillin-resistant Staphylococcus aureus) and C difficile infections – came from soil microbes.
With antimicrobial resistance continuing to rise globally, we urgently need new approaches and treatments. Plants may be an underexplored source of both new antimicrobial compounds and of compounds that make existing drugs more effective.
The story of tormentil shows how nature and traditional medicine can work hand in hand with modern science to address today’s challenges. It also highlights that solutions can be found in unexplored places – even in a small yellow wildflower growing in a bogland.
Ronan McCarthy receives funding from the UKRI, BBSRC, MRC and NERC.
John Walsh receives funding from the Department of Justice, Ireland for funding the project ‘Unlocking Nature’s Pharmacy from Bogland Species (UNPBS)’ under grant number DOJProject209825
Kavita Gadar receives funding from BBSRC.