The role of P fimbriae for Escherichia coli establishment and mucosal inflammation in the human urinary tract

Sammanfattning: Bacterial adhesion to the bladder mucosa is a critical step for the establishment of Escherichia coli bacteriuria. The P-fimbriae, encoded by the pap gene cluster, are considered as virulence factors but the mechanisms have been debated. This study defined the roles for P fimbriation during the early colonization of the human urinary tract. Patients with recurrent UTI were first subjected to deliberate colonization with the non-fimbriated ABU strain E. coli 83972. Bacteriuria was established long term (1-4 years) in patients with dysfunctional bladders, but not in the patients with normal bladder function. Super-infections were transient and asymptomatic (Paper 1). P fimbriae enhanced the establishment of bacteria in the human urinary tract. P fimbriated transformants of the ABU strain (E. coli 83972pap+/prs+) reached 105 CFU/ml more rapidly than E. coli 83972 and the vector control. This was demonstrated by group wise and intra-individual analysis, in patients colonized on different occasions with E. coli 83972 or the P fimbriated transformants (Paper 2). P fimbriated E. coli triggered the host response more efficiently than the ABU strain. Higher neutrophil numbers and IL-8 and IL-6 concentrations in urine were obtained after colonization with the P fimbriated transformants. These results demonstrated that transformation of E. coli 83972 with the pap sequences is sufficient to convert it to a more potent host response inducer (Paper 3). The P fimbriae were shown to lower the significant bacteriuria threshold. The P fimbriated transformants needed lower bacterial numbers (103-4 CFU/ml) to predict a positive second urine culture with a > 80% accuracy and to trigger a significant host response (Paper 4). The expression of P fimbriae in vivo was monitored using a gfp reporter gene construct. Following inoculation, E. coli 83972pap+ gfp+ adhered to the uroepithelial cells. A host response was triggered, and the cells were cleared from adherent bacteria. In parallell, neutrophils containing GFP protein were detected. The results demonstrated that P fimbriae mediate adherence in the human urinary tract, and illustrate the complex interaction with the host response exemplified by neutrophils (Paper 5). These studies show that P fimbriae fulfil the Koch Henles molecular postulates for bacterial establishment and host response induction in the human urinary tract.