Expression characteristics of the plasmid-borne colistin resistance gene.

The plasmid-encoded colistin resistance gene () has recently been reported in various Gram-negative species. However, the expression profile of remains unknown. Here, we investigated the expression of in various plasmids and bacteria. The expression levels in pMCR1_IncX4 varied from 1.81 × 10 to 1.05 × 10 (pmol per μg total RNA) in the two strains SZ03 and SZ04 (ST25) and the two strains SZ01 and CDA6 (ST2448 and ST167, respectively). The expression levels of pMCR1_IncI2 in E. coli SZ02 (ST2085) and BJ13 (ST457) were 5.27 × 10 and 2.58 × 10, respectively. In addition, the expression of chromosomal in ST156 BJ10 was 5.49×10. Interestingly, after 4μg/ml colistin treatment, mcr-1 in pMCR1_IncX4 increased 2- and 4-fold at 20 and 120 mins, respectively, in all pMCR1_IncX4-harboring strains, except for ST2448 , which had a lower expression after 20 mins that restored to baseline levels after 120 mins. In contrast, expression of pMCR1_IncI2 in the two strains (SZ02, BJ13) and the chromosomal in (BJ10) remained at baseline levels after 20 and 120 mins. In the same genetic background host strain E600, expression of pMCR1_IncX4 and pMCR1_IncI2 were similar and were decreased after colistin treatment for 20 min. However, in pMCR1_IncX4 was up-regulated after colistin treatment for 120 min, while in pMCR1_IncI2 was down-regulated compared to the untreated control. Our results suggested that has distinct expression profiles on different plasmids, bacterial hosts, and after antibiotic treatment.