Do type 1 fimbriae promote inflammation in the human urinary tract?

Type 1 fimbriae have been implicated as virulence factors in animal models of urinary tract infection (UTI), but the function in human disease remains unclear. This study used a human challenge model to examine if type 1 fimbriae trigger inflammation in the urinary tract. The asymptomatic bacteriuria strain Escherichia coli 83972, which fails to express type 1 fimbriae, due to a 4.25 kb fimB-fimD deletion, was reconstituted with a functional fim gene cluster and fimbrial expression was monitored through a gfp reporter. Each patient was inoculated with the fim+ or fim- variants on separate occasions, and the host response to type 1 fimbriae was quantified by intraindividual comparisons of the responses to the fim+ or fim- isogens, using cytokines and neutrophils as end-points. Type 1 fimbriae did not promote inflammation and adherence was poor, as examined on exfoliated cells in urine. This was unexpected, as type 1 fimbriae enhanced the inflammatory response to the same strain in the murine urinary tract and as P fimbrial expression by E. coli 83972 enhances adherence and inflammation in challenged patients. We conclude that type 1 fimbriae do not contribute to the mucosal inflammatory response in the human urinary tract.

Mucosal host responses to bacteriuria in colonic and ileal neobladders.

OBJECTIVE: To study the local host response in patients with colonic and ileal neobladders, with or without bacteriuria. METHODS: Twenty-three patients with colonic neobladders and 19 with ileal neobladders were included. Eleven radical prostatectomy patients and seven healthy male volunteers were used as controls. Six urine samples were obtained from all patients and controls over a six-month period. The samples were cultured semiquantitatively, and the number of neutrophils and concentrations of the inflammatory mediators interleukin 6 and 8 (IL-6, IL-8) in the urine were determined. RESULTS: The prostatectomy patients and healthy volunteers had sterile urine, and concentrations of IL-6 and IL-8 were below the detection limit. Most (>70%) of the urine samples from patients with colonic and ileal neobladders showed anaerobic or aerobic bacterial growth, and uropathogens were identified in about 45% of the samples. The local host response was minimal or undetectable in the sterile urine samples. However, the host response was markedly induced by uropathogenic strains in the urine, but not by urinary carriage of nonpathogenic or anaerobic strains. IL-8, but not IL-6, was increased in colonic neobladders, which corresponds to the mucosal host responses in patients with intact lower urinary tracts and asymptomatic bacteriuria. In ileal neobladders, the IL-8 responses were higher, and levels of IL-6 were significantly increased. CONCLUSION: Neobladders exhibit a significant local host response to colonization with bacterial uropathogens. This reaction is more pronounced and includes IL-6 activation in ileal neobladders than in colonic neobladders.

Uropathogenic Escherichia coli as a model of host-parasite interaction.

Resistance to mucosal infection varies greatly in the population, but the molecular basis of disease susceptibility is often unknown. Studies of host-pathogen infections are helpful to identify virulence factors, which characterise disease isolates, and successful defence strategies of hosts that resist infection. In the urinary tract infection (UTI) model, we have identified crucial steps in the pathogen-activated innate host response, and studied the genetic control of these activation steps. Furthermore, genetic variation in the innate host-response defence is investigated as a basis of disease susceptibility. The Toll-like receptor 4 (TLR4) controls initial mucosal response to uropathogenic Escherichia coli (UPEC). Bacterial TLR4 activation in epithelial cells leads to chemokine secretion and neutrophil recruitment and TLR4 mutant mice develop an asymptomatic carrier state. The chemokine receptor CXCR1 determines the efficiency of neutrophil migration and activation, and thus of bacterial clearance. CXCR1 mutant mice become bacteremic and develop renal scars and studies in UTI prone children have detected low CXCR1 expression, suggesting that CXCR1 is also essential for human disease susceptibility.

Escherichia coli, fimbriae, bacterial persistence and host response induction in the human urinary tract.

Urinary tract infections (UTI) are among the most common bacterial infections in humans. Symptomatic UTIs may be acute, recurrent or chronic but the most frequent form of UTI is asymptomatic bacteruria (ABU). In ABU, the mucosa remains inert, despite the presence of large bacterial numbers in urine. The difference in disease severity reflects the virulence of the infecting strain and the propensity of the host to respond to infection. It is essential to understand the molecular basis of disease diversity and the molecular interactions between bacteria and host that determine asymptomatic carriage and the transition to disease. We discuss the initial interactions between bacteria and the mucosal surfaces in the human urinary tract, and the bacterial factors involved in the breach of mucosal inertia. Specifically, the contribution of P and type 1 fimbriae to bacterial establishment and host response induction are investigated. The results show that P fimbriae serve as independent virulence factors when expressed by an ABU strain, by promoting the establishment of bacteriuria and the innate host response, which is the cause of symptoms and tissue damage. P fimbriae thus fulfil the molecular Koch postulates as independent virulence factors in the human urinary tract. Type 1 fimbriae, in contrast, did not act as virulence factors in this model, and thus appear to serve a different function in man than in the murine model.

PapG-dependent adherence breaks mucosal inertia and triggers the innate host response.

Mucosal pathogens differ from normal flora constituents in that they provoke a host response that upsets mucosal integrity. We investigated whether the elaboration of discrete adherence factors is sufficient to break the inertia of the mucosal barrier. PapG-mediated adherence was selected as an example, because P fimbrial expression characterizes uropathogenic Escherichia coli and because adherence starts the attack on the mucosal barrier. Patients were inoculated intravesically with transformed nonvirulent E. coli strains expressing functional P fimbriae (E. coli pap(+)) or mutant fimbriae lacking the adhesin (E. coli Delta papG). E. coli pap(+) was shown to activate the innate host response, and adherent gfp(+) bacteria were observed on excreted uroepithelial cells. E. coli Delta papG failed to trigger a response and was nonadhesive. We conclude that PapG-mediated adherence breaks mucosal inertia in the human urinary tract by triggering innate immunity and propose that this activation step differentiates asymptomatic carriage from infection.