B-259. Role of L-fucose and Resident Commensal Escherichia coli Strains in Inhibiting E. coli EDL933 (O157:H7) Growth in the Mouse Intestine

S. M. Autieri1, M. P. Leatham1, R. Mercado-Lubo1, D. C. Laux1, T. Conway2, P. S. Cohen1;
1Univ. of Rhode Island, Kingston, RI, 2Univ. of Oklahoma, Norman, OK.

E. coli EDL933, an O157:H7 strain, colonizes the streptomycin-treated CD-1 mouse intestine when it is the only E. coli strain fed to mice; but is eliminated when fed to mice pre-colonized with E. coli MG1655, a human commensal strain. In the present study, evidence is presented that accumulation of an intermediate of L-fucose catabolism, possibly L-fuculose-1-phosphate, limits E. coli EDL933 growth under these conditions. When mice were fed 105 CFU each of wildtype E. coli EDL933 and an E. coli EDL933 ΔfucAO mutant, which accumulates L-fuculose-1-phosphate, the wildtype E. coli EDL933 was found to be the better intestinal colonizer, colonizing at levels three to four orders of magnitude higher than the E. coli EDL933 ΔfucAO mutant. Surprisingly, an E. coli EDL933 ΔfucK mutant, which can’t convert L-fuculose to L-fuculose-1-phosphate, was found to be a better colonizer than wildtype E. coli EDL933, colonizing at a level two orders of magnitude higher than the wildtype E. coli EDL933. When mice were precolonized with E. coli MG1655 for 10 days and then fed either 105 of wildtype E. coli EDL933 or the E. coli EDL933 ΔfucK mutant, within a few days wildtype E. coli EDL933 was essentially eliminated from the intestine, but the E. coli EDL933 ΔfucK mutant grew about 1000-fold, to the level of the precolonized E. coli MG1655. Mice were also pre-colonized with either E. coli HS or E. coli Nissle1917, two other commensal strains, for 10-days and then fed 105 CFU of either wildtype E.coli EDL933 or the E. coli EDL933 ΔfucK mutant. Interestingly, the E. coli HS failed to provide protection against growth of either the wildtype E. coli EDL933 or the E. coli EDL933 ΔfucK mutant in the intestine. In contrast, E. coli Nissle1917, a probiotic strain used to treat gastrointestinal infections in humans, eliminated both the wildtype E.coli EDL933 and the E.coli EDL933 ΔfucK mutant from the intestine. Therefore, E. coli EDL933 growth in the mouse intestine appears to be influenced by at least two factors, the L-fucose concentration and the ability of E. coli EDL933 to compete with resident commensal E. coli strains.