SURVIVAL RATE OF MICE AFTER TRANSIENT COLONIZATION WITH ESCHERICHIA-COLI CLONES CARRYING VARIANT SHIGA-LIKE TOXIN TYPE-II OPERONS

We have previously employed a streptomycin-treated mouse model to demo nstrate that Escherichia coli clones expressing particular variant Shi ga-like toxin type II operons differ in oral virulence, as judged by m edian survival time. Differences in virulence were not seen between al l toxin variants, including two which differed significantly in cytoto xicity for Vero cells. In the present study, we have modified the anim al model by withdrawing antibiotic selection and reintroducing normal mouse intestinal flora at various times after oral challenge with thre e different variant SLT-II-producing clones. This resulted in a transi ent colonization more akin to that seen in natural human infections. T his has enabled detection of significant differences in survival rate between mice challenged with E. coli clones producing different SLT-II variants, which were not observed when colonization was maintained at high levels. (C) 1996 Academic Press Limited.