Researchers create antimicrobial substances using lignin and plant wastes

Researchers at the University of Nebraska-Lincoln are working to transform plant wastes, lignin in particular, into antimicrobial materials. The team, led by Shudipto Dishari, and Ross McCollum, associate professor of chemical and biomolecular engineering, explored the use of lignin, an abundant organic material and an important element in plant cell walls, in making sustainable antimicrobial substances.

They refined lignin from Norway spruce trees with quaternary ammonium, a cationic functional group typically used to destroy molds, bacteria, and viruses. The lignin-derived antimicrobial known as QAL was tested on wild-type and antibiotic-resistant E. coli. Thanks to the positive elements in the QAL, the lignin could combat the negatively charged outer bacterial skin.

The treatment lasted an hour and was promising. It delivered about 90% dead cells and between 90 to 100% growth inhibition.

What the scientists learned

Results published in American Chemical Society’s Sustainable Chemistry and Engineering journal showed the QAL prevented bacterial growth without posing threat to the human embryonic kidney cells. 

‘’While antibiotic-resistant bacteria are smart enough to save themselves from the action of conventional drugs, they cannot protect themselves from the non-specific effects that QAL makes,’’ Dishari said.

She believes we can ‘’get the best of both worlds if we can design low-cost, highly effective antimicrobials using green and eco-friendly materials.’’

According to the United Nations, drug-resistant illnesses may cause 10 million deaths by 2050. While researchers have successfully used synthetic materials to develop antimicrobials, it has come at a cost and with environmental implications.

This highlights the importance of the new study by Dishari and her team. ‘’By converting an untapped agricultural/process waste like lignin into value-added antimicrobials, we can significantly lower the expense of antimicrobial treatments and coatings in large-scale applications,’’ she noted.

Lignin is an untapped resource

The world produces over 100 million tons of lignin in a year, but the full potential of this natural resource is yet to be tapped. ‘’From a broader perspective, sustainable, scalable production of low-cost, efficient antimicrobials from waste lignin can help to sustain pulp and paper industries, biorefineries and agricultural farms and support the bioeconomy,’’ the lead researcher said.

Using lignin from Norway spruce trees for this study isn’t restrictive. In fact, it has offered opportunities to tackle drug-resistant cells with biorenewable agents.

According to Dishari, ‘’the chemical structure of lignin can vary depending on the plant source, but we are up to embracing this challenge as an exciting opportunity to play with lignin chemistry and design a wide range of antimicrobials with high efficacy.’’

This isn’t the first promising trial aimed at tackling antibiotic resistance. Scientists at the Royal Melbourne Institute of Technology (RMIT) and the University of South Australia (UniSA) tested black phosphorus-based nanotechnology against drug-resistant bacteria, including superbugs.

The findings published in Advanced Therapeutics revealed that the invention killed over 99% of bacteria without endangering other cells in biological models. It closed wounds by 80% within seven days.

“The beauty of our innovation is that it’s not simply a coating–it can actually be integrated into common materials that devices are made of, as well as plastic and gels, to make them antimicrobial,” said the co-lead researcher from RMIT, Professor Sumeet Walia.

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