Type 1 fimbriae contribute to catheter-associated urinary tract infections caused by Escherichia coli.

Biofilm formation on catheters is thought to contribute to persistence of catheter-associated urinary tract infections (CAUTI), which represent the most frequent nosocomial infections. Knowledge of genetic factors for catheter colonization is limited, since their role has not been assessed using physicochemical conditions prevailing in a catheterized human bladder. The current study aimed to combine data from a dynamic catheterized bladder model in vitro with in vivo expression analysis for understanding molecular factors relevant for CAUTI caused by Escherichia coli. By application of the in vitro model that mirrors the physicochemical environment during human infection, we found that an E. coli K-12 mutant defective in type 1 fimbriae, but not isogenic mutants lacking flagella or antigen 43, was outcompeted by the wild-type strain during prolonged catheter colonization. The importance of type 1 fimbriae for catheter colonization was verified using a fimA mutant of uropathogenic E. coli strain CFT073 with human and artificial urine. Orientation of the invertible element (IE) controlling type 1 fimbrial expression in bacterial populations harvested from the colonized catheterized bladder in vitro suggested that the vast majority of catheter-colonizing cells (up to 88%) express type 1 fimbriae. Analysis of IE orientation in E. coli populations harvested from patient catheters revealed that a median level of ∼73% of cells from nine samples have switched on type 1 fimbrial expression. This study supports the utility of the dynamic catheterized bladder model for analyzing catheter colonization factors and highlights a role for type 1 fimbriae during CAUTI.

In vitro Dynamic Model of a Catheterized Bladder and Biofilm Assay.

Biofilm formation on catheters is thought to contribute to persistence of catheter-associated urinary tract infections (CAUTI) which represent the most frequent nosocomial infections. Understanding of factors relevant for CAUTI pathogenesis and evaluation of new therapeutics or interference strategies requires a model system that mirrors the physico-chemical conditions prevailing in a catheterized human bladder. The described in vitro dynamic model of a catheterized bladder enables to emulate many of the characteristics of a catheterized human bladder albeit in the absence of a bladder epithelium. A minor modification compared to the original model system (Stickler, et al., 1999) allows temperature maintenance of the top 10 cm of the catheter, thereby enabling reproducible monitoring of biofilm formation on the internal catheter surface.