Antagonism of intestinal bacteria isolated from human infants against Escherichia coli O157:H7 infection in gnotobiotic mice

The protective role of intestinal flora against enteric infection is well known. Escherichia coli O157:H7 is one of the major causes of human enteritis. The aim of this study was to elucidate the composition of infant intestinal microbiota which prevents E. coli O157:H7 infection in hosts. We inoculated human infant faeces into germ-free mice and produced babyflora- associated (BFA) mice. The ability of the intestinal bacteria of BFA mice to eliminate E. coli O157:H7 was examined using gnotobiotic mice. Two groups of BFA (BFA-3 and BFA-4) mice showed different responses to E. coli O157:H7 infection. Orally challenged E. coli O157:H7 was eliminated from BFA-3 mice, whereas BFA-4 mice became carriers of E. coli O157:H7. There were remarkable differences in the composition of faecal flora between BFA-3 and BFA-4 mice, especially Bifidobacterium and Clostridium species. Using gnotobiotic mice, we found that enterobacteriaceae of BFA-3 mice are indispensable for the elimination. Enterococci and bifidobacteria appeared to support the protective function of enterobacteriaceae. The combination of aerobes from BFA-4 mice and bifidobacteria from BFA-3 mice instead of anaerobes from BFA-4 mice was capable of eliminating E. coli O157:H7. Enterobacteriaceae and Bifidobacterium species which are peculiar to human infants were important members of the microbiota to eliminate E. coli O157:H7 from their intestine. Key words: infant intestinal flora, gnotobiotic mice , Escherichia coli O157:H7, enterobacteriaceae, Bifidobacterium