Two newfound genes help to shield bacteria from tigecycline, which doctors use to treat drug-resistant infections.

A potent antibiotic of last resort is under threat from swiftly spreading bacterial genes that allow microbes to shrug off the drug’s effects.

Developed in the 1990s, the drug tigecycline is used to fight Escherichia coli as well as bacteria that cause pneumonia and other life-threatening illnesses. Tigecycline provides a key line of defence against antibiotic-resistant bacteria, including organisms that have recently evolved resistance to colistin, another antibiotic of last resort.

By sampling Chinese pig farms, supermarket meat counters and other sites, Jianzhong Shen and Yang Wang at China Agricultural University in Beijing and their colleagues identified two genes that protect bacteria from tigecycline and other antibiotics. Both genes were found riding on circles of DNA that can roam from one bacterium to another, and shed genes as they travel. Samples from hospital patients also contained the tigecycline-resistance genes.

The authors say that global surveillance for these genes is urgently needed.