Molecular Epidemiology and Colistin Resistant Mechanism of mcr -Positive and mcr -Negative Clinical Isolated Escherichia coli

Transmissible colistin resistance mediated by the gene has been reported worldwide, but clinical isolates of -negative colistin-resistant are rarely reported. The aim of this study was to evaluate the mechanism of colistin resistance among -positive and -negative clinical isolates by performing a molecular epidemiological surveillance. For the first time ever, we show nearly the same isolation ratio for -negative and -positive colistin-resistant clinical isolates (47.5 and 52.5%, respectively), with no demonstrable nosocomial transmission. We provide evidence for the prevalence of the -positive IncX4 plasmid and its high potential for horizontal transfer, with no obvious sequence type (ST) preference. In addition, the minimal inhibitory concentrations (MICs) of colistin of the -negative isolates were obviously higher than those of -positive isolates. Apart from the usually detected genes, i.e., , and , other genes may be associated with the colistin resistance in -negative . To the best of our knowledge, this is the first paper to report the molecular epidemiological surveillance and the proper mechanism of colistin resistance in -negative clinical isolates. Together, the results show that colistin resistance was prevalent not only in the -positive clinical isolates but also in the -negative isolates.