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Horse dung has scientists on scent of antibiotic success

Unlike other antibiotics, the compound is a protein 
and offers a different mode of action

European biologists have discovered a bacteria-killing compound in common mushrooms that grow in horse dung. Unusually for an antibiotic, copsin is a protein; but laboratory trials showed it to have the same effect on bacteria as traditional antibiotics.

The scientific community hopes to be able to develop a new range of antibiotics to replace those that are increasingly losing their ability to work against infections like tuberculosis (TB). A research team led by Markus Aebi, professor of mycology at ETH Zurich (the Swiss Federal Institute of Technology in Zurich), believe they may have found the answer.

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They discovered copsin in the common inky cap mushroom Coprinopsis cinerea that grows on manure, while researching how the fungus and various bacteria affected each other’s growth. According to lead researcher, post-doc Andreas Essig, horse manure’s rich substrate is key.

“Horse dung is a very rich substrate that harbours a diversity of micro-organisms, including fungi and bacteria,” said Essig. “Now these micro-organisms are in a constant competition for nutrients and space and it’s therefore very likely to find potent antibiotics in such an environment, which are used by the different organisms to inhibit the growth of the competitors.”

Essig and his colleagues from ETH Zurich and the University of Bonn cultivated the fungus in a laboratory, along with several different types of bacteria, and found that C. cinerea killed certain bacteria. Further research demonstrated that the copsin produced by the mushroom was responsible for this antibiotic effect.

Copsin is a protein, whereas traditional antibiotics are often non-protein organic compounds. It belongs to the group of defensins, a class of small proteins produced by numerous to counter disease-causing micro-organisms. In fact, the human body produces defensins in the skin and mucous membranes to protect itself against infections.

Essig says copsin’s inherent stability is crucial to its potential use and that it could be useful in the food industry, because it kills pathogens such as Listeria, a type of bacteria that can cause severe food poisoning. “Copsin is an exceptionally stable protein, so you can for example boil it at 100 F, you can put it in strong acid for hours,” he said.

Aebi says it is not certain whether copsin could be used in an antibiotic, but that even if it cannot it remains important research.

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