FIG 4.

Expression of five selected genes in clinical isolate 68A with and without colistin exposure. The genes are the plasmid-located mcr-9, qseB, and qseC as well as the chromosome-located pmrA (DNA-binding response regulator) and pmrB (sensor protein) genes. Fold changes in mRNA levels were determined by RT-qPCR. The data have been normalized to values for reference 16S rRNA genes. Three independent replicates were performed; the data shown represent the means, and the error bars represent standard deviations. The asterisks indicate statistical significance at different levels by analysis of variance: *, P ≤ 0.1; **, P ≤ 0.05; ***, P ≤ 0.01; ****, P ≤ 0.001; *****, P ≤ 0.0001. The different colistin concentrations used in our assays are shown by color, with blue indicating no colistin, red indicating 4 μg/ml colistin, and green indicating 8 μg/ml colistin.