Analysis of Serial Isolates of -Positive Escherichia coli Reveals a Highly Active IS Transposon.

The emergence of a transferable colistin resistance gene () is of global concern. The insertion sequence IS is a key component in the mobilization of this gene, but its role remains poorly understood. Six isolates were cultured from the same patient over the course of 1 month in Germany and the United States after a brief hospitalization in Bahrain for an unconnected illness. Four carried as determined by real-time PCR, but two were negative. Two additional -negative isolates were collected during follow-up surveillance 9 months later. All isolates were analyzed by whole-genome sequencing (WGS). WGS revealed that the six initial isolates were composed of two distinct strains: an initial ST-617 strain harboring and a second, unrelated, -negative ST-32 strain that emerged 2 weeks after hospitalization. Follow-up swabs taken 9 months later were negative for the ST-617 strain, but the -negative ST-32 strain was still present. was associated with a single copy of IS, located on a 64.5-kb IncI2 plasmid that shared >95% homology with other IncI2 plasmids. IS copy numbers ranged from 2 for the first isolate to 6 for the final isolate, but IS movement was independent of Some movement was accompanied by gene disruption, including the loss of genes encoding proteins involved in stress responses, arginine catabolism, and l-arabinose utilization. These data represent the first comprehensive analysis of IS movement in serial clinical isolates and reveal that, under certain conditions, IS is a highly active IS element whose movement may be detrimental to the host cell.