Newly published findings by a team of researchers in China describe the discovery of a plasmid-mediated mechanism in E. coli isolated from pigs that confers resistance to colistin – widely regarded as an antibiotic of last resort for treating drug resistant infections.
The researchers discovered the mechanism during a surveillance project looking at antibiotic resistance in E. coli from food animals when they found a large increase in the prevalence of colistin resistance in isolates. Further investigation revealed that a strain isolated from a pig, SHP45, possessed colistin resistance that could be transferred horizontally to another strain.
These findings led to the identification of a gene, mcr-1, conferring resistance to colistin and located on a plasmid within the bacterial cell. This is the first time that a resistance mechanism against polymyxin antibiotics like colistin has been found that is plasmid mediated and can be transferred horizontally to other bacteria.
Further studies revealed that the mcr-1 gene was present in E. coli isolates from 78 of 523 raw meat samples collected between 2011 and 2014 and in 166 of 804 animals. It was also found in 1% of samples taken from infected humans. The researchers showed that the plasmid containing the gene could be readily transferred to other bacteria.
The authors of the study say that the mcr-1 gene is currently confined to China, but warn that it is likely to spread rapidly to other countries. Their findings are published in the journal The Lancet Infectious Diseases and an abstract can be found here.