Mechanisms of microbial-host interaction during asymptomatic bacteriuria

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

Bacterial control of host gene expression through RNA polymerase II

The normal flora furnishes the host with ecological barriers that prevent pathogen attack while maintaining tissue homeostasis. Urinary tract infections (UTIs) constitute a highly relevant model of microbial adaptation in which some patients infected with Escherichia coil develop acute pyelonephritis, while other patients with bacteriuria exhibit an asymptomatic carrier state similar to bacterial commensalism. It remains unclear if the lack of destructive inflammation merely reflects low virulence or if carrier strains actively inhibit disease-associated responses in the host. Here, we identify a new mechanism of bacterial adaptation through broad suppression of RNA polymerase II-dependent (Pol II-dependent) host gene expression. Over 60% of all genes were suppressed 24 hours after human inoculation with the prototype asymptomatic bacteriuria (ABU) strain E. coil 83972, and inhibition was verified by infection of human cells. Specific repressors and activators of Pol II-dependent transcription were modified, Pol II phosphorylation was inhibited, and pathogen-specific signaling was suppressed in cell lines and inoculated patients. An increased frequency of strains inhibiting Pol II was epidemiologically verified in ABU and fecal strains compared with acute pyelonephritis, and a Pol II antagonist suppressed the disease-associated host response. These results suggest that by manipulating host gene expression, ABU strains promote tissue integrity while inhibiting pathology. Such bacterial modulation of host gene expression may be essential to sustain asymptomatic bacterial carriage by ensuring that potentially destructive immune activation will not occur

Toll-Like Receptor 4 Promoter Polymorphisms: Common TLR4 Variants May Protect against Severe Urinary Tract Infection

10.1371/journal.pone.0010734PLoS ONE55

Host Imprints on Bacterial Genomes—Rapid, Divergent Evolution in Individual Patients

Bacteria lose or gain genetic material and through selection, new variants become fixed in the population. Here we provide the first, genome-wide example of a single bacterial strain's evolution in different deliberately colonized patients and the surprising insight that hosts appear to personalize their microflora. By first obtaining the complete genome sequence of the prototype asymptomatic bacteriuria strain E. coli 83972 and then resequencing its descendants after therapeutic bladder colonization of different patients, we identified 34 mutations, which affected metabolic and virulence-related genes. Further transcriptome and proteome analysis proved that these genome changes altered bacterial gene expression resulting in unique adaptation patterns in each patient. Our results provide evidence that, in addition to stochastic events, adaptive bacterial evolution is driven by individual host environments. Ongoing loss of gene function supports the hypothesis that evolution towards commensalism rather than virulence is favored during asymptomatic bladder colonization

Rare emergence of symptoms during long-term asymptomatic E. coli 83972 carriage, without altered virulence factor repertoire.

Asymptomatic bacteriuria (ABU), established by intravesical inoculation of E.coli 83972, is protective in patients with recurrent UTI. In an RCT cross-over study, two patients developed three symptomatic UTI episodes while carrying E.coli 83972. This study examined if a reacquisition of virulence by symptom isolates may account for the switch from ABU to symptomatic UTI

Genetics of innate immunity and UTI susceptibility.

A functional and well-balanced immune response is required to resist most infections. Slight dysfunctions in innate immunity can turn the 'friendly' host defense into an unpleasant foe and give rise to disease. Beneficial and destructive forces of innate immunity have been discovered in the urinary tract and mechanisms by which they influence the severity of urinary tract infections (UTIs) have been elucidated. By modifying specific aspects of the innate immune response to UTI, genetic variation either exaggerates the severity of acute pyelonephritis to include urosepsis and renal scarring or protects against symptomatic disease by suppressing innate immune signaling, as in asymptomatic bacteriuria (ABU). Different genes are polymorphic in patients prone to acute pyelonephritis or ABU, respectively, and yet discussions of UTI susceptibility in clinical practice still focus mainly on social and behavioral factors or dysfunctional voiding. Is it not time for UTIs to enter the era of molecular medicine? Defining why certain individuals are protected from UTI while others have severe, recurrent infections has long been difficult, but progress is now being made, encouraging new approaches to risk assessment and therapy in this large and important patient group, as well as revealing promising facets of 'good' versus 'bad' inflammation

Genetic studies of body mass index yield new insights for obesity biology

Note: A full list of authors and affiliations appears at the end of the article. Obesity is heritable and predisposes to many diseases. To understand the genetic basis of obesity better, here we conduct a genome-wide association study and Metabochip meta-analysis of body mass index (BMI), a measure commonly used to define obesity and assess adiposity, in up to 339,224 individuals. This analysis identifies 97 BMI-associated loci (P 20% of BMI variation. Pathway analyses provide strong support for a role of the central nervous system in obesity susceptibility and implicate new genes and pathways, including those related to synaptic function, glutamate signalling, insulin secretion/action, energy metabolism, lipid biology and adipogenesis.</p