Analysis of the gene that makes bacteria resistant to colistin has shown that it emerged in 2005 in China, in pigs, and then spread very quickly around the world.

Colistin, like other polymyxin antibiotics, is considered a "last resort" drug. They are not particularly safe and can cause a number of side effects, so they are used when other antibiotics are no longer effective. Although colistin is used relatively rarely in humans, the number of bacterial strains resistant to it has increased dramatically in recent years.

Antibiotic resistance genes are often located on plasmids—autonomous extrachromosomal genetic elements that can be easily transferred from one bacterium to another. The colistin resistance gene is located on a plasmid called MCR-1 (mobilized colistin resistance). While the gene doesn't provide complete protection, it does force doctors to significantly increase the antibiotic dose, making treatment unsafe for the patient.

Although colistin is rarely used in humans, it has found widespread use in livestock farming: antibiotics are added to livestock feed en masse not only to combat pathogenic microbes but also to promote weight gain.

Recently, scientists from University College London studied the spread of the mcr-1 plasmid and discovered that it may have emerged as early as 2005 in China, most likely on a pig farm. MCR-1 came to the scientists' attention in 2016, when it had already been detected on every inhabited continent except Australia. A total of 457 colistin-resistant bacterial strains have been identified, including those belonging to the genera Escherichia, Salmonella, and Klebsiella.

The rapid spread of the resistance gene astonished the researchers. They believe that this is not the only gene that makes bacteria resistant to colisitin. In any case, the spread of antibiotic resistance is a global problem that requires the coordinated efforts of doctors and scientists worldwide.

In addition to promoting the rational use of antibiotics and reducing their use in agriculture, experts recommend intensifying the search for and use of alternative antimicrobial drugs.

* Ruobing Wang, Lucy van Dorp, Liam P. Shaw, Phelim Bradley, et al. The global distribution and spread of the mobilized colistin resistance gene mcr-1 // Nature Communications, 2018, 9: 1179 . doi:10.1038/s41467-018-03205-z