FIG 2.

MotA and MotB contribute to APEC virulence. (A) The expression of motA and motB was significantly downregulated in the arcA mutant in response to duck serum under microaerobic (5% oxygen) conditions. (B) Deletion of motAB did not affect the growth of APEC XM in either LB or serum under either aerobic or microaerobic conditions. Bacterial strains were grown in LB and serum under both aerobic and microaerobic conditions, and the optical density at 600 nm (OD₆₀₀) was monitored every 2 h. The experiments were performed at least three times in quadruplicate. (C) Deletion of motAB resulted in attenuation of APEC XM. The motAB mutant and the WT (1 × 10⁵ CFU) were inoculated into 10 7-day-old ducks per group, and the mortality was monitored for 1 week. The virulence of the motAB mutant was significant attenuated compared to that of the WT strain (P < 0.05 by Fisher's exact test.).