A new gene¹ (mcr-1) that enables bacteria to be highly resistant² to polymyxins, the last line of antibiotic³ defence we have left, is widespread in Enterobacteriaceae [1] taken from pigs and patients in south China, including strains with epidemic⁴ potential, according to new research published in The Lancet Infectious Diseases. The mcr-1 gene was found on plasmids, mobile DNA⁵ that can be easily copied and transferred between different bacteria, suggesting an alarming potential to spread and diversify⁶ between different bacterial⁷ populations.

 

"These are extremely worrying results. The polymyxins (colistin and polymyxin B) were the last class of antibiotics⁸ in which resistance was incapable⁹ of spreading from cell to cell. Until now, colistin resistance resulted from chromosomal¹⁰ mutations, making the resistance mechanism¹¹ unstable¹² and incapable of spreading to other bacteria,"[2] explains author Professor Jian-Hua Liu from South China Agricultural University in Guangzhou, China. 

 

"Our results reveal the emergence¹³ of the first polymyxin resistance gene that is readily passed between common bacteria such as Escherichia coli and Klesbsiella pneumoniae, suggesting that the progression from extensive drug resistance to pandrug resistance is inevitable¹⁴."[2]

 

During routine testing of food animals for antimicrobial resistance in China, Liu and colleagues isolated¹⁵ an E coli strain (SHP45) from a pig on an intensive pig farm in Shanghai that showed resistance to colistin that could be transferred to another strain. This prompted the researchers to collect bacteria samples from pigs at slaughter¹⁶ across four provinces, and from pork and chicken sold in 30 open markets and 27 supermarkets across Guangzhou between 2011 and 2014. They also analysed bacteria samples from patients presenting with infections to two hospitals in Guangdong and Zhejiang provinces. Samples were tested for antibiotic susceptibility and the mcr-1 gene using polymerase chain reaction (PCR) and sequencing.

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