CpxR facilitates interbacterial competition of APEC in vitro. The indicated APEC donor and recipient strains were co-incubated at a ratio of 5:1, as shown by the dashed line. After incubation for 6 h at 30 °C, the donor and recipient strains were recovered. The competition outcomes between donor and recipient strains were calculated and are shown. A, B The interbacterial competition activities of wild-type, mutant and complemented strains were compared. C The interbacterial competition activity was also measured in the wild-type and mutant strains with NlpE overexpression. Statistical significance was assessed by using one-way ANOVA. (*P < 0.05; **P < 0.01).