Genome-based analyses of fitness effects and compensatory changes associated with acquisition of blaCMY, blaCTX-M, and blaOXA-48/VIM-1 containing plasmids in Escherichia coli

Resistance plasmids are under selective conditions beneficial for the bacterial host, but in the absence of selective pressure this carriage may cause fitness costs. Compensation of this fitness burden is important to obtain competitive ability under antibiotic-free conditions. In this study we investigate fitness effects after a conjugative transfer of plasmids containing various beta-lactamase genes transferred into E. coli. Transconjugants demonstrating highest growth differences were selected and challenged in long-term growth experiments. Growth rates were assessed at different time points during growth for 500 generations. Whole genome sequencing of initial and evolved transconjugants revealed genomic changes over time. Most plasmid acquisitions resulted in minor growth deficiencies only. Transfer of a single blaCMY-16 carrying plasmid resulted in a growth burden and a growth benefit in independent matings. Long-term growth led to a compensation of fitness burdens and benefits. Analysing WGS determined genomic changes over time.