Figure 2.

The presence of the afa-1 operon in haemagglutinating E coli correlates with diffuse adherence and invasion to HEp-2 epithelial cells. Giemsa stain of HEp-2 cells infected with E coli strains. (A) All eight haemagglutinin-positive library clones showed diffuse adherence to cell cultures. (B) Eight haemagglutination (HA)-negative fosmid clones chosen at random from the library were non-adherent. (C) Colonic mucosally associated E coli HM358 exhibited a diffusely adherent pattern as per diffusely adherent E coli C1845. The E coli K12 plating strain EPI300T1 containing pCC1Fos was non-adherent. (D) The eight haemagglutination-positive fosmid library clones possessing the afa-1 gene cluster, exhibiting diffuse adherence, showed increased ability to invade Hep-2 cells compared to haemagglutination-negative clones. Invasion calculated as percentage of the original inoculums (multiplicity of infection 10) and expressed relative to E coli LF82 previously shown to be invasive in this cell line.² * p<0.05 and *** p<0.001 when compared to the non-invasive plating strain EPI300-T1 containing pCC1Fos alone (mean±SEM; N=3 experiments, each performed with n=3 replicates; Kruskal–Wallis).