Fig. 3

E. coli O91:H21 exhibits greater virulence compared to O22:H8. A Increased adhesion of E. coli O91:H21 to colon epithelial cells. CT26 cells: bacteria = 1: 10. Scale bar = 20 μm. N: Nuclei, White arrows: Bacteria surrounding or attaching CT26 cells. Lower: Quantitative bacterial counts adhering to one CT26 cell. n = 27–29 cells/group. ***P < 0.001. B More cell death induced by E. coli O91:H21 infection. CT26 cells: bacteria = 1:10, Green: live cells; Red: dead cells. Scale bar = 200 µm. Right: Quantitation of dead CT26 cell counts/field. n = 11 fields/group, *P < 0.05. C Increased E. coli O91:H21 in the colon lumen of GF mice. Red: E. coli, Blue: Nuclei. Scale bar = 50 μm. Right: Quantitation of E. coli⁺ fluorescence intensity in colon lumen (50 µm in diameter) of GF mice infected with E. coli O91:H21 or E. coli O22:H8. n = 37 areas (50 µm in diameter) from 4 mice per group, ****P < 0.0001. D Increased CFU of E. coli O91:H21 in the feces of GF mice. Right: Quantitative CFU (Log10) per g stool from GF mice infected with E. coli O91:H21 as compared to mice infected with E. coli O22:H8, n = 4 mice/group, **P < 0.01. E Increased levels of LPS in the feces and serum of GF mice infected with E. coli O91:H21. n = 3 mice/group, *P < 0.05, ***P < 0.001. F E. coli O91:H21 formed larger colonies on the colon mucosa of GF mice. Red: E. coli colonies; Blue: Nuclei. Scale bar = 100 μm. Right: Quantitative E. coli colonies in the colon of GF mice infected with E. coli O91:H21 or E. coli O22:H8. n = 29 colonies from 3 mice per group, ***P < 0.001. G Increased colon epithelial cell death in E. coli O91:H21 inoculated GF mice. Red: PI + cells in colon mucosa, Blue: Nuclei. Scale bar = 50 μm. Right: Quantitative PI + cells/field. n = 11–13 fields from 3 mice per group. **P < 0.01. H Increased ulcer formation in the colon mucosa of GF mice infected with E. coli O91:H21. Scale bar = 100 µm. Black arrows: Ulcer. Right: Quantitative number of ulcer in the colon mucosa. n = 17–23 fields from 5 mice/group. ***P < 0.001