Mechanisms of microbial-host interaction during asymptomatic bacteriuria

Abstract: Urinary tract infections (UTIs) present an interesting and relevant model for studying microbial adaptation. After establishing significant numbers, the bacteria either cause severe disease, or an asymptomatic carrier state resembling the normal flora at other mucosal sites. Patients with asymptomatic bacteriuria (ABU) are protected from re-infection if the strain that they carry outcompetes more pathogenic strains. Deliberate inoculation with the prototypic ABU strain Escherichia coli 83972 has therefore been developed and clinically proven to protect against recurrent UTI. To define the host influence on bacterial adaptation during long term E. coli 83972 ABU, we collected sequential isolates from patients that had been inoculated with E. coli 83972 and established stable bacteriuria. The isolates acquired several host-specific mutations, demonstrating that E. coli 83972 adapts to the individual host. Each host provided a unique niche, which was demonstrated by significant variations of mucosal host response parameters between patients. Variation in the host response to ABU has lead to uncertainty about the use of host response parameters as a basis for diagnostic and therapeutic decisions. In 23 patients, the host response to E. coli 83972 was accompanied by a low but host-specific increase in neutrophil chemotaxis but IL-6 levels did not increase. To define the effects of genetic variation on the urine proteomic host response, patients were genotyped for polymorphisms that have been linked to susceptibility to ABU and urine samples from the patients were screened for 31 immune markers. The genetic polymorphisms in the interferon regulatory factor 3 (IRF3) and Toll-like receptor 4 (TLR4) promoter had a significant impact on the magnitude of the host response during E. coli 83972 ABU, which consisted of mainly innate immune mediators. The transcriptional host response to ABU has not been examined in humans. To examine if ABU strains affect uroepithelial and leukocyte human host gene expression, we analyzed peripheral blood leukocytes from patients colonized by E. coli 83972 and uroepithelial cells stimulated with the same strain. E. coli 83972 inhibited RNA Polymerase II phosphorylation and suppressed pathogen-specific pathways in both systemic leukocytes and uroepithelial. We show that ABU is an active rather than passive process, and present a theory that basal transcriptional suppression may be a general mechanism used by commensal strains to modulate host gene expression. We further examined the kinetics of the local and systemic host response during ABU and the effect of type 1 and P fimbrial adhesion on the transcriptional signature. All patients inoculated with E. coli 83972pap activated the Interferon signaling pathway. Two patients inoculated with E. coli 83972fim downregulated Natural Killer cell signaling. Our results provide direct molecular evidence of host specific evolution of bacterial genomes as well as transcriptomic alterations in the host during ABU.