Exploiting a conjugative CRISPR/Cas9 system to eliminate plasmid harbouring the mcr-1 gene from Escherichia coli

The transfer of multi-drug-resistance plasmids by bacterial conjugation is largely responsible for the development of drug resistance in bacteria, and causes serious problems in the treatment of infectious diseases. Since the first discovery of plasmid-borne colistin resistance gene mcr-1 was reported in late 2016, this gene has been found in a great number of Escherichia coli and other Gram-negative pathogens separated from different types of sources worldwide. The elimination of plasmids carrying mcr-1 and restoration of polymyxin sensitivity has very important clinical significance because polymyxins are frequently used as last-resort antibiotics to treat extensively drug-resistant Gram-negative bacterial infections. A host-independent conjugative plasmid was constructed in this study, and an engineered CRISPR/Cas9 system was used to remove plasmid harbouring mcr-1 from bacteria. This study found that this conjugative plasmid can not only be used as a new tool to remove resistance plasmids and sensitize the recipient bacteria to antibiotics, but can also make the recipient cell acquire immunity against mcr-1. This strategy provides a novel method to counteract the ever-worsening spread of mcr-1 among bacterial pathogens.