C3 deposition on E. coli isolates. 6 E. coli isolates (lane 3–8) were incubated with 5% NHS in culture medium for 30 minutes. C3 deposition was detected by Western blot analysis. Lane1, Purified C3b (0.1 μg); lane 2 J96 were incubated with 5% NHS; lanes 3–5 isolates showing positive for C3-dependent internalisation (U1, U5, B2); lanes 6–8, isolates not showing C3-dependent internalisation (U9, U13, B7). The presence of C3b is indicated by 105 kDa (α' chain) and 75 kDa (β chain) bands, iC3b by 75 kDa (β chain), 67 kDa (α1 chain), and 40 kDa (α2 chain) bands.