Scientists have found in the wild in Germany a gene that was first detected in China and which makes bacteria resistant to colistin, often hailed as the "last-resort" antibiotic.
Called mcr-1, the gene was detected in a human bacteria sample and is widespread in farm animals, reported Germany's Institute for Risk Assessment (BfR) and the Hanover University of Veterinary Medicine.
Colistin is administered in Germany predominantly for treating intestinal disease in farm animals, the BfR said. In human medicine it is used to treat infections by bacteria resistant to other, better-tolerated antibiotics.
Experts are alarmed, because mcr-1 is the first known resistance gene for colistin that is able to move freely among different strains of bacteria. It can be passed on from harmless intestinal bacteria to pathogens, thus making these pathogens harder to treat.
Germany's University of Giessen, where mcr-1 was detected in the human bacteria sample, said the bacteria had also shown resistance to carbapenems, a class of antibiotics used to treat infections known or suspected to be caused by multidrug-resistant bacteria.
If such bacteria are resistant to colistin as well, it warned, "a hopeless situation without a treatment option can arise."
First detected in China in late 2015, mcr-1 is particularly known to make the intestinal bacteria Escherichia coli and salmonella in poultry resistant to colistin, the BfR said.
According to the Berlin-based Robert Koch Institute (RKI), which is responsible for disease control and prevention, use of the relatively old antibiotic has increased in recent years as "a last-resort therapy option" in cases of drug-resistant bacterial infections.
Doctors had tended to avoid it because its side effects are significant.
After farm animals and humans in China were found to have mcr-1, whose presence some scientists attribute to the frequent use of colistin in Chinese livestock production, German samples of colistin-resistant bacteria were examined for the gene.
Scientists say the latest finds indicate that mcr-1 has been present in Germany at least since 2011.
It remains unclear, however, how widespread it is and in which direction it's transferable between animals and humans. Older bacteria samples are now to be examined.
The BfR said Danish authorities had reported detection of the resistance gene in poultry meat samples from Germany in early December 2015. Tests conducted in other European countries yielded positive results in farm animals and humans too.
Christian Meyer, agriculture minister of the north-western German state of Lower Saxony, has called for an end to what he said was the excessive use of antibiotics in animal farming. His state's share of the antibiotics administered to animals in Germany is more than half, he noted.
"If we don't change course, we're headed straight for a post-antibiotics era," Meyer remarked, warning that at some point there may be no effective antibiotics of last resort left, which would pose a general threat to health.
The initial reports by Chinese scientists on the discovery of the resistance gene for colistin in many farm animals and meat samples as well as hospital patients caused concern, said Petra Gastmeier, director of the Institute of Hygiene and Environmental Medicine at Berlin's Charite hospital.
"Still, we thought, 'China's far away,'" she said.
Should colistin, too, lose its efficacy, she pointed out, all that would remain are combination therapies of more than one medication. She said it was important that physicians and veterinarians work closely together to come to grips with the problem of antibiotic resistance.
"The use (in animal farming) of last-resort antibiotics that are especially important for human health should be totally prohibited," declared Hubert Weiger, chairman of Friends of the Earth Germany, an environmental protection organization.
The group said some 16 tons of last-resort antibiotics had been used in German animal farming since 2014, adding that the amounts had increased despite the overall decrease in antibiotics use in animals.
For protection against disease-causing bacteria in meat, the BfR says consumers should "carefully observe the rules of kitchen hygiene" to ensure that no bacteria are transferred from raw meat to other foods. In addition, meat should be thoroughly cooked before consumption.