Identification and characteristics of the dctR gene mutant and complemented strains. A Schematic chart and confirmation of the dctR gene mutant and complemented strains by PCR. The dctR gene was replaced by the FRT site in the mutant strain. The primers used for the PCR identification of the dctR gene deletion are also indicated. The amplification of the corresponding target genes indicate the success in mutant and complemented strain construction. B Transcriptional level analysis of dctR and its flanking genes by qRT-PCR. Deletion of dctR did not affect the expression of the flanking genes slp and chuS. Moreover, no transcription of dctR was observed in the mutant strain. C Bacterial growth curves. APEC strains were grown in LB at 37 °C, and the OD600nm was measured every hour. Mutant strain ΔdctR shows similar growth rate with the wild-type and complemented strains. D Bacterial motility. The motility diameter of the mutant strain was similar with those of the wild-type and complemented strains. Each value represents the average of three independent experiments. Significant differences were detected using one-way ANOVA (***P < 0.001).