Specific fosmid clones are selected during intestinal colonisation. Restriction enzyme analysis of fosmid pools before and after inoculation into mice. 10 colonies were randomly picked from plating of the inoculum fed to two mice on day 0 (A, lanes 2–11). On day 17 postfeeding, 4 colonies were picked from plating of faeces from each of the two mice (B and C, lanes 2–5). Fosmids were isolated and cut with restriction enzyme Sal I. The presented data (shown here for fosmid pool 1) are representative for all 12 fosmid pools.