Precolonized Human Commensal Escherichia coli Strains Serve as a Barrier to E. coli O157:H7 Growth in the Streptomycin-Treated Mouse Intestine

Different Escherichia coli strains generally have the same metabolic capacity for growth on sugars in vitro, but they appear to use different sugars in the streptomycin-treated mouse intestine (Fabich et al., Infect. Immun. 76:1143-1152, 2008). Here, mice were precolonized with any of three human commensal strains (E. coli MG1655, E. coli HS, or E. coli Nissle 1917) and 10 days later were fed 10⁵ CFU of the same strains. While each precolonized strain nearly eliminated its isogenic strain, confirming that colonization resistance can be modeled in mice, each allowed growth of the other commensal strains to higher numbers, consistent with different commensal E. coli strains using different nutrients in the intestine. Mice were also precolonized with any of five commensal E. coli strains for 10 days and then were fed 10⁵ CFU of E. coli EDL933, an O157:H7 pathogen. E. coli Nissle 1917 and E. coli EFC1 limited growth of E. coli EDL933 in the intestine (10³ to 10⁴ CFU/gram of feces), whereas E. coli MG1655, E. coli HS, and E. coli EFC2 allowed growth to higher numbers (10⁶ to 10⁷ CFU/gram of feces). Importantly, when E. coli EDL933 was fed to mice previously co-colonized with three E. coli strains (MG1655, HS, and Nissle 1917), it was eliminated from the intestine (