If you became infected with bad gut bacteria, like the sometimes deadly E. coli or Klebsiella, the antibiotic colistin could save your life. Researchers discovered the substance in 1947, but since the 1980s it is hardly used in humans. This is because of its strong side effects. Colistin can damage the kidneys, for example.
Yet, these side effects are exactly what make the substance so valuable: Because it is rarely used, hardly any resistance has developed in humans. The drug can be used when other antibiotics, like cephalosporin and carbapenem, fail. In 2012, the WHO put colistin on its list of „critically important antibiotics.“
You can see the resistance against different antibiotics in Europe in our suberbug atlas.
In meat production, the situation is different. Here, colistin has been one of the most popular antibiotics for years. Veterinarians predominantly prescribe it to treat gut infections in farm animals. Experts estimate that the total consumption worldwide is 12.000 tons per year.
The justification for such extensive use? The drug is seldom used to treat humans. And arising resistance would be limited to bugs that infect animals. It was assumed that colistin is one of the few antibiotics whose resistance genes cannot move from germ to germ.
This notion was knocked down by Chinese scientists. They saw more and more bugs developing resistance to colistin and became suspicious: Is there a resistance gene that can jump from bug to bug after all?
It turned out that yes, there is: The scientists collected E. coli from pig farms and demonstrated that the bacteria can transmit the resistance, even across species. The culprit is a gene, called mcr-1, that makes changes to the bacterial wall, preventing colistin from docking onto it. The researchers discovered that mcr-1 is widespread among animal bugs. Even more concerning is that the gene was also found in some germs which infect humans.
In December 2015, events escalated: The European Medical Agency announced it will reconsider its recommendations regarding the use of colistin in farming. And scientists started looking for the resistance gene in their regions. They discovered the gene in Thailand, Denmark, Holland and France — and at the beginning of January in Germany. The Federal Institute for Risk Assessment investigated old samples and found the newly discovered colistin gene most frequently in E. coli from poultry.
Another German research group was also successful. They found the new gene in four samples: Three of them stemmed from pigs, one from a human wound.