In vivo detection of Escherichia coli type 1 fimbrial expression and phasevariation during experimental urinary tract infection

Adhesion mediated by fimbriae is thought to play an important role in the p athogenesis of urinary tract infections (UTI) by Escherichia coli. The majo rity of clinical isolates of E. coli from UTI are able to express type 1 fi mbriae. However, the importance of these fimbriae as a virulence factor has been controversial. To investigate the expression of type 1 fimbriae in vi vo during UTI, mice were transurethrally infected with uropathogenic E. col i C175-94 and type 1 fimbrial expression was determined directly by two ind ependent methods at 2 h, 1 d and 3 d after infection. By use of an assay co mbining in situ rRNA hybridization and immunofluorescence, all bacterial ce lls detected in urine, bladders and kidneys from mice sacrificed 1 and 3 d after onset of infection were found to express type 1 fimbriae. In contrast , the majority of cells in the suspension used for infection of mice and sp ecimens from mice sacrificed 2 h after inoculation were found to be non-fim briated. Similar results were obtained with a PCR assay revealing the orien tation of the invertible promoter driving the transcription of type 1 fimbr ial genes. Whilst the promoter in both ON and OFF positions could be amplif ied from the suspension used for infection and specimens from mice sacrific ed 2 h after inoculation, at 1 and 3 d after onset of infection only the pr omoter in the ON orientation could be amplified. These results show that in troduction of E. coli C175-94 into the mouse urinary tract leads to markedl y enhanced expression of type 1 fimbriae.