Polymyxin antibiotics are used as last-resort therapies to treat infections caused by multidrug-resistant Gram-negative bacteria. The plasmid-mediated colistin resistance determinant MCR-1 has been identified in Enterobacteriaceae in China in Nov. 2015.

　　In a recent study of 2066 bloodstream infection isolates (1495 Escherichia coli and 571 Klebsiella pneumoniae) in a large cross-section of Chinese hospitals, Dr. Yunsong Yu and his colleagues found that only 21 (1.0%) were mcr-1positive, of which 20 (1.3%) were E. coli and only one (0.2%) was K. pneumoniae. Only one of these mcr-1 positive isolates was carbapenem resistant. The 21 mcr-1-positive isolates were clonally diverse and carried mcr-1 on two types of plasmids, a 33 kb IncX4 plasmid and a 61 kb Inc12 plasmid. The 30 day mortality of the patients with bloodstream infections caused by mcr-1-positive isolates was zero. These results indicated that mcr-1-positive isolates from bloodstream infections were rare, sporadic, and remained susceptible to many antimicrobial agents. E. coli, rather than K. pneumoniae, was the main host of the mcr-1 gene. Further studies are needed to clarify the clinical impact of this novel resistance gene.

　　This work was published in Lancet Infect Dis entitled “Prevalence of mcr-1 inEscherichia coli and Klebsiella pneumoniae recovered from bloodstream infections in China: a multicenter longitudinal study” on January 27th, 2017. This study was funded by the National Natural Science Foundation of China.