Downloaded from www.microbiologyresearch.org by IP: 54.70.40.11 On: Fri, 02 Aug 2019 11:57:33 Microbiology (1999), 145, 2683–2690 Printed in Great Britain In vivo detection of Escherichia coli type 1 fimbrial expression and phase variation during experimental urinary tract infection Carsten Struve and Karen Angeliki Krogfelt Author for correspondence : Karen Angeliki Krogfelt. Tel : 45 3268 3745. Fax: 45 3268 3873. e-mail : kakssi.dk Department of Gastrointestinal Infections, Statens Serum Institut, 5 Artillerivej, 2300 Copenhagen 5, Denmark Adhesion mediated by fimbriae is thought to play an important role in the pathogenesis of urinary tract infections (UTI) by Escherichia coli. The majority of clinical isolates of E. coli from UTI are able to express type 1 fimbriae. However, the importance of these fimbriae as a virulence factor has been controversial. To investigate the expression of type 1 fimbriae in vivo during UTI, mice were transurethrally infected with uropathogenic E. coli C175-94 and type 1 fimbrial expression was determined directly by two independent methods at 2 h, 1 d and 3 d after infection. By use of an assay combining in situ rRNA hybridization and immunofluorescence, all bacterial cells 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 specimens from mice sacrificed 2 h after inoculation were found to be non-fimbriated. Similar results were obtained with a PCR assay revealing the orientation of the invertible promoter driving the transcription of type 1 fimbrial genes. Whilst the promoter in both ON and OFF positions could be amplified from the suspension used for infection and specimens from mice sacrificed 2 h after inoculation, at 1 and 3 d after onset of infection only the promoter in the ON orientation could be amplified. These results show that introduction of E. coli C175-94 into the mouse urinary tract leads to markedly enhanced expression of type 1 fimbriae. Keywords : type 1 fimbriae, phase variation, urinary tract infection, in situ hybridization, immunofluorescence INTRODUCTION Escherichia coli is the pathogen responsible for most cases of uncomplicated urinary tract infections (UTI), one of the most frequent human infectious disorders (Sobel, 1991). Fimbriae mediate the ability of E. coli cells to adhere to the uroepithelium, thereby resisting elim- ination by the flow of urine. Adhesion is therefore considered an important step in the pathogenesis of UTI (Reid & Sobel, 1987). Among the different types of fimbrial adhesins, P fimbriae have been identified as an important virulence factor among uropathogenic E. coli strains (Donnenberg & Welch, 1996). The role of type 1 fimbriae in pathogenesis has been less clear, especially due to the ubiquity of the fimbriae, as they are found on ................................................................................................................................................. Abbreviation : UTI, urinary tract infections. approximately 70 % of all E. coli isolates and most P- fimbriated E. coli strains also possess type 1 fimbriae (Orndorff & Bloch, 1990 ; Hagberg et al., 1981). Furthermore, in vitro adherence studies of either purified type 1 fimbriae or type-1-fimbriated E. coli strains to formaldehyde-fixed human tissue and to exfoliated epithelial cells from the urine gave contradictory results (Fujita et al. 1989; Virkola 1987; Ørskov et al. 1980). Recent studies of UTI with animal models show that type-1-fimbriated E. coli cells are better colonizers of the urinary tract than their isogenic mutants (Connell et al., 1996 ; Langermann et al., 1997 ; Sokurenko et al., 1998 ; Mulvey et al., 1998). Type 1 fimbriae mediate adhesion to structures con- taining -mannose, but have also been shown to mediate binding to non-glycosylated peptide epitopes (Sokurenko et al., 1994). The fim gene cluster, consisting 0002-3288  1999 SGM 2683