Effect of Bifidobacterium-Monoassociation and Feeding of Fructooligosaccharides on Lethal Activity of Enterohemorrhagic Escherichia coli O157 in Germ-Free Mice

抄録

A gnotobiotic mouse study was investigated to establish a suitable experimental model for evaluating an individual bacterial role for Escherichia coli O157: H7 infection. Germ-free (GF) BALB/c mice (nu/+) were found to die after 12-14 days of E. coli O157: H7 (strain CR 7087) infection, causing rough surface, atrophy, and faded color of the kidney, while specific pathogen-free (SPF) mice survived without any damage after similar infection. Using this model, the effect of Bifidobacterium-monoassociation (BA) and feeding of fructooligosaccharides (FOS) on the lethal activity of enterohemorrhagic E. coli O157: H7 was examined to elucidate if mice inoculated with B. adolescentis strain MBL8321 showed a significantly longer survival time than original GF mice after E. coli O157: H7 (strain CR 7087) infection. An analysis of the biomarkers in the present study provided the following information: 1) B. adolescentis was successfully associated at the 10⁹-10¹⁰ colony-forming unit (cfu) level throughout the test period, 2) the numbers of viable E. coli in feces decreased in the order of GF, BA (= BA-FOS) and SPF groups, and the amount of fecal Shiga toxin (Stx), serum creatinine and urea nitrogen also decreased in similar order, 3) the amount of cecal short-chain fatty acids (SCFAs) was found to correlate with the survival time, and 4) the feeding of FOS under this condition afforded no additional increase in either survival time or amount of cecal SCFAs. These results indicate that the study using gnotobiotic mice is suitable for an experimental model of E. coli O157: H7 infection, and suggest tha the intestinal microflora plays an important role for preventing E. coli O157 infection in mice. However, the model is not suitable for evaluating the inhibitory effect related to intestinal fermentation because the parameters for fermentation did not change.