Fig. 2

Migration and invasive abilities of the AIEC LF82 strain are promoted depending on the increase in fliC expression. A Representative images of the bacterial growth zones (swimming diameters) for non-AIEC K12 and AIEC LF82 strains. Each bacterial strain (OD₅₇₀ = 1.0) was added to the center of a plate containing Luria Bertani (LB) medium containing 0.3% agar and incubated at 37 °C for 16 h. B Bacterial swimming diameters on LB agar plates were measured using the ImageJ software. Data are presented as mean ± SD. *P < 0.05, **P < 0.01; P-values were determined using the student’s t-test. C In vitro infection model using Transwell inserts. Caco-2 cells grown on the insert were incubated with the bacteria at a multiplicity of infection (MOI) of 1:100 (1 × 10⁵ bacteria/well) for 30 min. Caco-2 cells grown on the inserts were incubated with the bacteria for 3 h and then washed and incubated for 3 h in Dulbecco’s modified Eagle medium (DMEM) containing 400 μg/mL kanamycin to kill extracellular bacteria. D Caco-2 cells were lysed with PBS containing 1% Triton X-100, and the lysates were plated on LB agar. Colony-forming units (CFU) were counted after 24 h of incubation. Data are presented as the mean ± SD. *P < 0.05, **P < 0.01; P-values were determined using the student’s t-test. E Bacterial counts in the colon were determined five days after infection. Mice were administered antibiotics (20 mg/L streptomycin and 1 g/L ampicillin) for 9 days and then orally inoculated with 1 × 10.⁹ CFU of LF82 and ΔfliC-LF82. The colon tissue was homogenized in PBS, and the homogenates were plated onto MacConkey agar containing 50 μg/mL ampicillin. The number of CFU was counted. Data are presented as mean ± SD (n = 5 per group)