G-CSF induction early in uropathogenic Escherichia coli infection of the urinary tract modulates host immunity

Comprehensive analysis of multiple cytokines to stratify uropathogenic Escherichia coli pathogenesis in mouse model of urinary tract infection

PURPOSE

Urinary tract infection (UTI) is one of the most common human bacterial infections primarily caused by uropathogenic E. coli (UPEC). Empiric treatment in UTI cause emergence of multidrug resistance and limit treatment options. Understanding UTI at the molecular level with respect to the causative pathogen as well as subsequent host response pose an absolute necessity towards appropriate clinical management. This study aimed to investigate host cytokine response in mouse UTI model with respect to bacterial colonization and associated virulence gene expression upon infection.

METHOD

Mouse UTI model was established with two clinical UPEC isolates E. coli NP105 and E. coli P025. UPEC colonization in bladder and kidney was evaluated by bacterial culture (CFU/ml). Histopathology of the tissues were examined by hematoxylin and eosin staining. PCR and real time PCR were used to detect the incidence and expression of respective bacterial genes. Cytokine concentrations in tissues and sera were evaluated using ELISA. GraphPad prism version 8.0.2 was used for statistical interpretation.

RESULT

Highest bacterial colonization was observed on 7th and 9th day post infection (p.i). in bladder and kidney of mouse infected with E. coli P025 and E. coli NP105 respectively with a distinct difference in relative expression of fimH and papC adhesin genes in vivo. IL-1β level in tissues and sera of E. coli NP105 and E. coli P025 infected mouse was significantly different but the IL-17A, GCSF, TGF-β levels were comparable.

CONCLUSION

These findings show a role of IL1β to stratify pathogenicity of UPEC in mouse UTI model.

Host response during unresolved urinary tract infection alters female mammary tissue homeostasis through collagen deposition and TIMP1

Exposure to pathogens throughout a lifetime influences immunity and organ function. Here, we explore how the systemic host-response to bacterial urinary tract infection (UTI) induces tissue-specific alterations to the mammary gland. Utilizing a combination of histological tissue analysis, single cell transcriptomics, and flow cytometry, we identify that mammary tissue from UTI-bearing mice displays collagen deposition, enlarged ductal structures, ductal hyperplasia with atypical epithelial transcriptomes and altered immune composition. Bacterial cells are absent in the mammary tissue and blood of UTI-bearing mice, therefore, alterations to the distal mammary tissue are mediated by the systemic host response to local infection. Furthermore, broad spectrum antibiotic treatment resolves the infection and restores mammary cellular and tissue homeostasis. Systemically, unresolved UTI correlates with increased plasma levels of the metalloproteinase inhibitor, TIMP1, which controls extracellular matrix remodeling and neutrophil function. Treatment of nulliparous and post-lactation UTI-bearing female mice with a TIMP1 neutralizing antibody, restores mammary tissue normal homeostasis, thus providing evidence for a link between the systemic host response during UTI and mammary gland alterations.

Secretory leukocyte protease inhibitor protects against severe urinary tract infection in mice

Millions suffer from urinary tract infections (UTIs) worldwide every year with women accounting for the majority of cases. Uropathogenic Escherichia coli (UPEC) causes most of these primary infections and leads to 25% becoming recurrent or chronic. To repel invading pathogens, the urinary tract mounts a vigorous innate immune response that includes the secretion of antimicrobial peptides (AMPs), rapid recruitment of phagocytes, and exfoliation of superficial umbrella cells. Here, we investigate secretory leukocyte protease inhibitor (SLPI), an AMP with antiprotease, antimicrobial, and immunomodulatory functions, known to play protective roles at other mucosal sites, but not well characterized in UTIs. Using a preclinical model of UPEC-caused UTI, we show that urine SLPI increases in infected mice and that SLPI is localized to bladder epithelial cells. UPEC-infected SLPI-deficient (Slpi-/-) mice suffer from higher urine bacterial burdens, prolonged bladder inflammation, and elevated urine neutrophil elastase (NE) levels compared to wild-type (Slpi+/+) controls. Combined with bulk bladder RNA sequencing, our data indicate that Slpi-/- mice have a dysregulated immune and tissue repair response following UTI. We also measure SLPI in urine samples from a small group of female subjects 18-49 years old and find that SLPI tends to be higher in the presence of a uropathogen, except in patients with a history of recent or recurrent UTI, suggesting a dysregulation of SLPI expression in these women. Taken together, our findings show SLPI promotes clearance of UPEC in mice and provides preliminary evidence that SLPI is likewise regulated in response to uropathogen exposure in women.IMPORTANCEAnnually, millions of people suffer from urinary tract infections (UTIs) and more than $3 billion are spent on work absences and treatment of these patients. While the early response to UTI is known to be important in combating urinary pathogens, knowledge of host factors that help curb infection is still limited. Here, we use a preclinical model of UTI to study secretory leukocyte protease inhibitor (SLPI), an antimicrobial protein, to determine how it protects the bladder against infection. We find that SLPI is increased during UTI, accelerates the clearance of bacteriuria, and upregulates genes and pathways needed to fight an infection while preventing prolonged bladder inflammation. In a small clinical study, we show SLPI is readily detectable in human urine and is associated with the presence of a uropathogen in patients without a previous history of UTI, suggesting SLPI may play an important role in protecting from bacterial cystitis.

Tamm-Horsfall protein augments neutrophil NETosis during urinary tract infection

Urinary neutrophils are a hallmark of urinary tract infection (UTI), yet the mechanisms governing their activation, function, and efficacy in controlling infection remain incompletely understood. Tamm-Horsfall glycoprotein (THP), the most abundant protein in urine, uses terminal sialic acids to bind an inhibitory receptor and dampen neutrophil inflammatory responses. We hypothesized that neutrophil modulation is an integral part of THP-mediated host protection. In a UTI model, THP-deficient mice showed elevated urinary tract bacterial burdens, increased neutrophil recruitment, and more severe tissue histopathological changes compared to WT mice. Furthermore, THP-deficient mice displayed impaired urinary NETosis during UTI. To investigate the impact of THP on NETosis, we coupled in vitro fluorescence-based NET assays, proteomic analyses, and standard and imaging flow cytometry with peripheral human neutrophils. We found that THP increases proteins involved in respiratory chain, neutrophil granules, and chromatin remodeling pathways, enhances NETosis in an ROS-dependent manner, and drives NET-associated morphologic features including nuclear decondensation. These effects were observed only in the presence of a NETosis stimulus and could not be solely replicated with equivalent levels of sialic acid alone. We conclude that THP is a critical regulator of NETosis in the urinary tract, playing a key role in host defense against UTI.

The NLRP3 Inflammasome Is Dispensable in Methicillin-Resistant Staphylococcus aureus Urinary Tract Infection

The NLRP3 inflammasome is a cytoplasmic complex that senses molecular patterns from pathogens or damaged cells to trigger an innate immune defense response marked by the production of proinflammatory cytokines IL-1β and IL-18 and an inflammatory death called pyroptosis. The NLRP3 inflammasome is activated in the urinary tract by a variety of infectious and non-infectious insults. In this study, we investigated the role of the NLRP3 inflammasome by comparing the pathophysiology of methicillin-resistant Staphylococcus aureus (MRSA) ascending UTI in wild-type (WT) and Nlrp3-/- mice. The difference in the bacterial burden detected in the urinary tracts of MRSA-infected WT and Nlrp3-/- was not statistically significant at 6, 24, and 72 h post-infection (hpi). The levels of pro-inflammatory cytokines and chemokines as well as the numbers of granulocytes recruited to bladder and kidney tissues at 24 hpi were also similar between Nlrp3-/- and WT mice. The histopathological analysis of MRSA-infected bladder and kidney sections from Nlrp3-/- and WT mice showed similar inflammation. Overall, these results suggest that MRSA-induced urinary NLRP3 activity does not play a role in the pathophysiology of the ascending UTI.

The Potential Role of Persister Cells in Urinary Tract Infections

PURPOSE OF REVIEW

This review explores the role of persister cells in urinary tract infections (UTIs). UTIs are one of the most common bacterial infections, affecting millions of people worldwide. Persister cells are a subpopulation of bacteria with dormant metabolic activity which allows survival in the presence of antibiotics.

RECENT FINDINGS

This review summarizes recent research on the pathogenesis of persister cell formation in UTIs, the impact of persister cells on the effectiveness of antibiotics, the challenges they pose for treatment, and the need for new strategies to target these cells. Furthermore, this review examines the current state of research on the identification and characterization of persister cells in UTIs, as well as the future directions for investigations in this field. This review highlights the importance of understanding the role of persister cells in UTIs and the potential impact of targeting these cells in the development of new treatments.

Secretory Leukocyte Protease Inhibitor Protects Against Severe Urinary Tract Infection in Mice

Millions suffer from urinary tract infections (UTIs) worldwide every year with women accounting for the majority of cases. Uropathogenic Escherichia coli (UPEC) causes most of these primary infections and leads to 25% becoming recurrent or chronic. To repel invading pathogens, the urinary tract mounts a vigorous innate immune response that includes the secretion of antimicrobial peptides (AMPs), rapid recruitment of phagocytes and exfoliation of superficial umbrella cells. Here, we investigate secretory leukocyte protease inhibitor (SLPI), an AMP with antiprotease, antimicrobial and immunomodulatory functions, known to play protective roles at other mucosal sites, but not well characterized in UTIs. Using a mouse model of UPEC-caused UTI, we show that urine SLPI increases in infected mice and that SLPI is localized to bladder epithelial cells. UPEC infected SLPI-deficient (Slpi-/-) mice suffer from higher urine bacterial burdens, prolonged bladder inflammation, and elevated urine neutrophil elastase (NE) levels compared to wild-type (Slpi+/+) controls. Combined with bulk bladder RNA sequencing, our data indicate that Slpi-/- mice have a dysregulated immune and tissue repair response following UTI. We also measure SLPI in urine samples from a small group of female subjects 18-49 years old and find that SLPI tends to be higher in the presence of a uropathogen, except in patients with history of recent or recurrent UTI (rUTI), suggesting a dysregulation of SLPI expression in these women. Taken together, our findings show SLPI protects against acute UTI in mice and provides preliminary evidence that SLPI is likewise regulated in response to uropathogen exposure in women.

Tissue-resident memory T cells mediate mucosal immunity to recurrent urinary tract infection

Urinary tract infection (UTI) is one of the most prevalent human bacterial infections. New therapeutic approaches, including vaccination and immunotherapy, are urgently needed to combat the rapid global dissemination of multidrug-resistant uropathogens. Development of therapies is impeded by an incomplete understanding of memory development during UTI. Here, we found that reducing bacterial load early in infection, by reducing the inoculum or with antibiotics after infection, completely abrogated the protective memory response. We observed a mixed T helper (T_H) cell polarization, composed of T_H1, T_H2, and T_H17 T cells, among T cells infiltrating the bladder during primary infection. Thus, we hypothesized that reducing antigen load altered T_H cell polarization, leading to poor memory. Unexpectedly, however, T_H cell polarization was unchanged in these scenarios. Instead, we uncovered a population of tissue-resident memory (T_RM) T cells that was significantly reduced in the absence of sufficient antigen. Demonstrating that T_RM cells are necessary for immune memory, transfer of lymph node- or spleen-derived infection-experienced T cells to naïve animals did not confer protection against infection. Supporting that T_RM cells are sufficient to protect against recurrent UTI, animals depleted of systemic T cells, or treated with FTY720 to block memory lymphocyte migration from lymph nodes to infected tissue, were equally protected compared with unmanipulated mice against a second UTI. Thus, we uncovered an unappreciated key role for T_RM cells in the memory response to bacterial infection in the bladder mucosa, providing a target for non-antibiotic-based immunotherapy and/or new vaccine strategies to prevent recurrent UTI.

The immune responses to different Uropathogens call individual interventions for bladder infection

Urinary tract infection (UTI) caused by uropathogens is the most common infectious disease and significantly affects all aspects of the quality of life of the patients. However, uropathogens are increasingly becoming antibiotic-resistant, which threatens the only effective treatment option available-antibiotic, resulting in higher medical costs, prolonged hospital stays, and increased mortality. Currently, people are turning their attention to the immune responses, hoping to find effective immunotherapeutic interventions which can be alternatives to the overuse of antibiotic drugs. Bladder infections are caused by the main nine uropathogens and the bladder executes different immune responses depending on the type of uropathogens. It is essential to understand the immune responses to diverse uropathogens in bladder infection for guiding the design and development of immunotherapeutic interventions. This review firstly sorts out and comparatively analyzes the immune responses to the main nine uropathogens in bladder infection, and summarizes their similarities and differences. Based on these immune responses, we innovatively propose that different microbial bladder infections should adopt corresponding immunomodulatory interventions, and the same immunomodulatory intervention can also be applied to diverse microbial infections if they share the same effective therapeutic targets.

A Systematic Review of the (Un)known Host Immune Response Biomarkers for Predicting Recurrence of Urinary Tract Infection

Recurrent urinary tract infections (rUTI) represent a major healthcare and economic burden along with a significant impact on patient’s morbidity and quality of life, even in the absence of well-known risk factors, such as vesicoureteral reflux. Despite numerous attempts to find a suitable therapeutic option, there is no clear benefit of any currently available intervention for prevention of UTI recurrence and its long-term consequences such as hypertension, renal scarring and/or insufficiency. The common treatment practice in many centers around the globe involves the use of continuous low-dose antibiotic prophylaxis, irrespective of various studies indicating increased microbial resistance against the prophylactic drug, leading to prolonged duration and escalating the cost of UTI treatment. Moreover, the rapid appearance of multi-drug resistant uropathogens is threatening to transform UTI to untreatable disease, while impaired host-microbiota homeostasis induced by a long-term use of antibiotics predisposes patients for various autoimmune and infectious diseases. New biomarkers of the increased risk of UTI recurrence could therefore assist in avoiding such outcomes by revealing more specific patient population which could benefit from additional interventions. In this light, the recent findings suggesting a crucial role of urothelial innate immunity mechanisms in protection of urinary tract from invading uropathogens might offer new diagnostic, prognostic and even therapeutic opportunities. Uroepithelial cells detect uropathogens via pattern recognition receptors, resulting in activation of intracellular signaling cascade and transcription factors, which ultimately leads to an increased production and secretion of chemokines, cytokines and antimicrobial peptides into the urinary stream. Emerging evidence suggest that the disturbance of a single component of the urinary tract innate immunity system might increase susceptibility for rUTI. The aim of the current review is to update clinicians and researchers on potential biomarkers of host immune response alterations predisposing for rUTI and propose those well worth exploring further. For this purpose, over a hundred original papers were identified through an extensive PubMed and Scopus databases search. This comprehensive review might enrich the current clinical practice and fill the unmet clinical needs, but also encourage the development of therapeutic agents that would facilitate urinary bacterial clearance by enhancing the host immune response.

Immunomodulation therapy offers new molecular strategies to treat UTI

Innovative solutions are needed for the treatment of bacterial infections, and a range of antibacterial molecules have been explored as alternatives to antibiotics. A different approach is to investigate the immune system of the host for new ways of making the antibacterial defence more efficient. However, the immune system has a dual role as protector and cause of disease: in addition to being protective, increasing evidence shows that innate immune responses can become excessive and cause acute symptoms and tissue pathology during infection. This role of innate immunity in disease suggests that the immune system should be targeted therapeutically, to inhibit over-reactivity. The ultimate goal is to develop therapies that selectively attenuate destructive immune response cascades, while augmenting the protective antimicrobial defence but such treatment options have remained underexplored, owing to the molecular proximity of the protective and destructive effects of the immune response. The concept of innate immunomodulation therapy has been developed successfully in urinary tract infections, based on detailed studies of innate immune activation and disease pathogenesis. Effective, disease-specific, immunomodulatory strategies have been developed by targeting specific immune response regulators including key transcription factors. In acute pyelonephritis, targeting interferon regulatory factor 7 using small interfering RNA or treatment with antimicrobial peptide cathelicidin was protective and, in acute cystitis, targeting overactive effector molecules such as IL-1β, MMP7, COX2, cAMP and the pain-sensing receptor NK1R has been successful in vivo. Furthermore, other UTI treatment strategies, such as inhibiting bacterial adhesion and vaccination, have also shown promise.

Hyperactivation of innate immunity is a disease determinant in urinary tract infections (UTIs). Modulation of innate immunity has promise as a therapy for UTIs. In this Review, the authors discuss potential mechanisms and immunomodulatory therapeutic strategies in UTIs.

Excessive innate immune responses to infection cause symptoms and pathology in acute pyelonephritis and acute cystitis.

Innate immunomodulation therapy is, therefore, a realistic option for treating these conditions.

Targeting excessive innate immune responses at the level of transcription has been successful in animal models.

Innate immunomodulation therapy reduces excessive inflammation and tissue pathology and accelerates bacterial clearance from infected kidneys and bladders in mice.

Innate immunomodulation therapy also accelerates the clearance of antibiotic-resistant bacterial strains.

Innate Bacteriostatic Mechanisms Defend the Urinary Tract

Urinary tract infection (UTI) is the most common type of urogenital disease. UTI affects the urethra, bladder, ureter, and kidney. A total of 13.3% of women, 2.3% of men, and 3.4% of children in the United States will require treatment for UTI. Traditionally, bladder (cystitis) and kidney (pyelonephritis) infections are considered independently. However, both infections induce host defenses that are either shared or coordinated across the urinary tract. Here, we review the chemical and biophysical mechanisms of bacteriostasis, which limit the duration and severity of the illness. Urinary bacteria attempt to overcome each of these defenses, complicating description of the natural history of UTI.

Biomarkers for febrile urinary tract infection in children

BACKGROUND

The sensitivity and specificity of the leukocyte esterase test for the diagnosis of urinary tract infection (UTI) are suboptimal. Recent studies have identified markers that appear to more accurately differentiate children with and without UTI. The objective of this study was to determine the accuracy of these markers, which included CCL3, IL-8, CXCL1, TNF-alpha, IL-6, IFN-gamma, IL-17, IL-9, IL-2, and NGAL, in the diagnosis of UTI.

METHODS

This was a prospective cross-sectional study to compare inflammatory proteins between urine samples from febrile children with a UTI, matched febrile controls without a UTI, and asymptomatic healthy controls.

RESULTS

We included 192 children (75 with febrile UTI, 69 febrile controls, and 48 asymptomatic healthy controls). Urinary proteins that best discriminated between febrile children with and without UTI were NGAL, a protein that exerts a local bacteriostatic role in the urinary tract through iron chelation; CCL3, a chemokine involved in leukocyte recruitment; and IL-8, a cytokine involved in neutrophil recruitment. Levels of these proteins were generally undetectable in asymptomatic healthy children.

CONCLUSIONS

NGAL, CCL3, and IL-8 may be useful in the early diagnosis of UTI.

TRIAL REGISTRATION

ClinicalTrials.gov (NCT01391793) A higher resolution version of the Graphical abstract is available as Supplementary information.

Modified horseshoe crab peptides target and kill bacteria inside host cells

Bacteria that occupy an intracellular niche can evade extracellular host immune responses and antimicrobial molecules. In addition to classic intracellular pathogens, other bacteria including uropathogenic Escherichia coli (UPEC) can adopt both extracellular and intracellular lifestyles. UPEC intracellular survival and replication complicates treatment, as many therapeutic molecules do not effectively reach all components of the infection cycle. In this study, we explored cell-penetrating antimicrobial peptides from distinct structural classes as alternative molecules for targeting bacteria. We identified two β-hairpin peptides from the horseshoe crab, tachyplesin I and polyphemusin I, with broad antimicrobial activity toward a panel of pathogenic and non-pathogenic bacteria in planktonic form. Peptide analogs [I11A]tachyplesin I and [I11S]tachyplesin I maintained activity toward bacteria, but were less toxic to mammalian cells than native tachyplesin I. This important increase in therapeutic window allowed treatment with higher concentrations of [I11A]tachyplesin I and [I11S]tachyplesin I, to significantly reduce intramacrophage survival of UPEC in an in vitro infection model. Mechanistic studies using bacterial cells, model membranes and cell membrane extracts, suggest that tachyplesin I and polyphemusin I peptides kill UPEC by selectively binding and disrupting bacterial cell membranes. Moreover, treatment of UPEC with sublethal peptide concentrations increased zinc toxicity and enhanced innate macrophage antimicrobial pathways. In summary, our combined data show that cell-penetrating peptides are attractive alternatives to traditional small molecule antibiotics for treating UPEC infection, and that optimization of native peptide sequences can deliver effective antimicrobials for targeting bacteria in extracellular and intracellular environments.

A Novel microRNA of Japanese Flounder Regulates Antimicrobial Immunity Involving a Bacteria-Binding CSF3

MicroRNAs (miRNAs) are small non-coding RNAs that regulate diverse biological processes including immunity. In a previous high-throughput RNA sequencing study, a novel miRNA, pol-miR-novel_642, was identified from Japanese flounder (Paralichthys olivaceus), a farmed fish species with important economic value. In this study, we investigated the regulatory mechanism and the function of pol-miR-novel_642 and its target gene. We found that pol-miR-novel_642 targeted, in a sequence-specific manner, a flounder gene encoding an uncharacterized protein that is a structural homologue of murine granulocyte colony stimulating factor 3 (CSF3). The expression of pol-miR-novel_642 and its target gene (named PoCSF3-1) was regulated, in different manners, by the bacterial pathogen Edwardsiella tarda and the viral pathogen megalocytivirus. Overexpression of pol-miR-novel_642 or interference with PoCSF3-1 expression in flounder cells strongly potentiated E. tarda infection. Consistently, in vivo knockdown of PoCSF3-1 enhanced bacterial dissemination in flounder tissues but blocked viral replication, whereas in vivo overexpression of PoCSF3-1 inhibited bacterial dissemination and facilitated viral infection. Overexpression/knockdown of PoCSF3-1 and pol-miR-novel_642 also affected the activation of autophagy. Recombinant PoCSF3-1 (rPoCSF3-1) interacted with and inhibited the growth of Gram-negative bacteria in a manner relying on a PoCSF3-1-characteristic structural motif that is absent in mouse CSF3. rPoCSF3-1 also regulated the proliferation, inflammatory response, and immune defense of flounder head kidney leukocytes in a structure-dependent fashion. Together, these results reveal the function of a novel miRNA-CSF3 regulatory system of flounder, and add new insights into the role and mechanism of fish miRNA and CSF3 in antimicrobial immunity.

Early invasion of the bladder wall by solitary bacteria protects UPEC from antibiotics and neutrophil swarms in an organoid model

Recurrence of uropathogenic Escherichia coli (UPEC) infections has been attributed to reactivation of quiescent intracellular reservoirs (QIRs) in deep layers of the bladder wall. QIRs are thought to arise late during infection following dispersal of bacteria from intracellular bacterial communities (IBCs) in superficial umbrella cells. Here, we track the formation of QIR-like bacteria in a bladder organoid model that recapitulates the stratified uroepithelium within a volume suitable for high-resolution live-cell imaging. Bacteria injected into the organoid lumen enter umbrella-like cells and proliferate to form IBC-like bodies. In parallel, single bacteria penetrate deeper layers of the organoid wall, where they localize within or between uroepithelial cells. These "solitary" bacteria evade killing by antibiotics and neutrophils and are morphologically distinct from bacteria in IBCs. We conclude that bacteria with QIR-like properties may arise at early stages of infection, independent of IBC formation and rupture.

Molecular determinants of disease severity in urinary tract infection

The most common and lethal bacterial pathogens have co-evolved with the host. Pathogens are the aggressors, and the host immune system is responsible for the defence. However, immune responses can also become destructive, and excessive innate immune activation is a major cause of infection-associated morbidity, exemplified by symptomatic urinary tract infections (UTIs), which are caused, in part, by excessive innate immune activation. Severe kidney infections (acute pyelonephritis) are a major cause of morbidity and mortality, and painful infections of the urinary bladder (acute cystitis) can become debilitating in susceptible patients. Disease severity is controlled at specific innate immune checkpoints, and a detailed understanding of their functions is crucial for strategies to counter microbial aggression with novel treatment and prevention measures. One approach is the use of bacterial molecules that reprogramme the innate immune system, accelerating or inhibiting disease processes. A very different outcome is asymptomatic bacteriuria, defined by low host immune responsiveness to bacteria with attenuated virulence. This observation provides the rationale for immunomodulation as a new therapeutic tool to deliberately modify host susceptibility, control the host response and avoid severe disease. The power of innate immunity as an arbitrator of health and disease is also highly relevant for emerging pathogens, including the current COVID-19 pandemic.

The Immune System Fails to Mount a Protective Response to Gram-Positive or Gram-Negative Bacterial Prostatitis

Bacterial prostatitis affects 1% of men, with increased incidence in the elderly. Acute bacterial prostatitis frequently progresses to chronicity, marked by recurrent episodes interspersed with asymptomatic periods of variable duration. Antibiotic treatment is standard of care; however, dissemination of antimicrobially resistant uropathogens threatens therapy efficacy. Thus, development of nonantibiotic-based approaches to treat chronic disease is a priority. Currently, why chronic prostatitis arises is unclear, as the immune response to prostate infection is incompletely understood. As 80% of prostatitis cases are caused by Gram-negative uropathogenic Escherichia coli (UPEC) or Gram-positive Enterococcus faecalis, we used a mouse transurethral instillation model to address the hypothesis that an innate immune response fails to develop following prostate infection with these uropathogens, leading to chronic disease. Surprisingly, infection induced robust proinflammatory cytokine expression and myeloid cell infiltration. Following a second infection, cytokine responses and innate cell infiltration were largely comparable to primary infection. Characteristic of memory responses, more lymphoid cells infiltrated the prostate in a second infection compared with a first, suggesting that adaptive immunity develops to eliminate the pathogens. Unexpectedly, bacterial burden in prostates challenged with either UPEC or E. faecalis was equal or greater than primary infection despite that a protective adaptive response to UPEC infection was evident in the bladder of the same animals. Our findings support that chronic or recurrent prostatitis develops despite strong innate immune responses and may be the result of a failure to develop immune memory to infection, pointing to actionable targets for immunotherapy.

Functionally distinct resident macrophage subsets differentially shape responses to infection in the bladder

Resident macrophages are abundant in the bladder, playing key roles in immunity to uropathogens. Yet, whether they are heterogeneous, where they come from, and how they respond to infection remain largely unknown. We identified two macrophage subsets in mouse bladders, MacM in muscle and MacL in the lamina propria, each with distinct protein expression and transcriptomes. Using a urinary tract infection model, we validated our transcriptomic analyses, finding that MacM macrophages phagocytosed more bacteria and polarized to an anti-inflammatory profile, whereas MacL macrophages died rapidly during infection. During resolution, monocyte-derived cells contributed to tissue-resident macrophage pools and both subsets acquired transcriptional profiles distinct from naïve macrophages. Macrophage depletion resulted in the induction of a type 1-biased immune response to a second urinary tract infection, improving bacterial clearance. Our study uncovers the biology of resident macrophages and their responses to an exceedingly common infection in a largely overlooked organ, the bladder.

Restriction of chronic Escherichia coli urinary tract infection depends upon T cell-derived interleukin-17, a deficiency of which predisposes to flagella-driven bacterial persistence

Urinary tract infections (UTI) frequently progress to chronicity in infected individuals but the mechanisms of pathogenesis underlying chronic UTI are not well understood. We examined the role of interleukin (IL)-17A in UTI because this cytokine promotes innate defense against uropathogenic Escherichia coli (UPEC). Analysis of UPEC persistence and pyelonephritis in mice deficient in IL-17A revealed that UPEC CFT073 caused infection at a rate higher than the multidrug resistant strain EC958. Il17a^-/- mice exhibited pyelonephritis with kidney bacterial burdens higher than those of wild-type (WT) mice. Synthesis of IL-17A in the bladder reflected a combination of γδ-T and T_H 17 cell responses. Analysis of circulating inflammatory mediators at 24h postinoculation identified predictors of progression to chronicity, including IL-6 and monocyte chemoattractant protein-1 (MCP-1). Histological analysis identified infiltrating populations of neutrophils, NK cells, and γδ T cells in the bladder, whereas neutrophils predominated in the kidney. Analysis of the contribution of flagella to chronicity using hyper-flagellated and fliC-deficient UPEC in WT and Il17a^-/- mice revealed that, in a host that is deficient for the production of IL-17A, flagella contribute to bacterial persistence. These findings show a role for IL-17A in defense against chronic UTI and a contribution of flagella to the pathogenesis of infection.

A Synthetic Peptide 2Abz23S29 Reduces Bacterial Titer and Induces Pro-Inflammatory Cytokines in a Murine Model of Urinary Tract Infection

Introduction

A urinary tract infection (UTI), which is often caused by uropathogenic E. coli (UPEC) strains, affects many people worldwide annually. UPEC causes the production of pro-inflammatory cytokines by the bladder epithelial cells; however, it has been proven that the UPEC can inhibit the early activation of the innate immune system.

Methods

This study aimed to examine the antibacterial and immunomodulatory effects of different doses of truncated alpha-defensins (human neutrophil peptide (HNP)-1) analog 2Abz²³S²⁹ on the mouse UTI model. Experimentally uropathogenic E. coli CFT073-infected mice were treated with low-dose 2Abz²³S²⁹ (250µg/mL), high-dose 2Abz²³S²⁹ (750µg/mL), ciprofloxacin (cip) (800µg/mL), or high-dose 2Abz²³S²⁹plus cip once a day 24 h post-infection. The 2Abz²³S²⁹ and cip treatment were given for two consecutive days.

Results

The in vivo results showed that fewer UPEC were recovered from the bladders of mice treated transurethrally with 2Abz²³S²⁹. Moreover, low-dose 2Abz²³S²⁹ significantly decreased the level of the interleukin-6 (IL-6), whereas high-dose 2Abz²³S²⁹ increased pro-inflammatory cytokines including IL-6, macrophage inflammatory protein/2 (MIP/2), tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-1β) in infected bladders of mice. Besides, the levels of cytokines IL-6 and MIP/2 in infected mice treated with a combination of high-dose 2Abz²³S²⁹ and cip were significantly higher than the untreated mice. In contrast, CFT073-infected mice treated with a combination of high-dose 2Abz²³S²⁹ and cip showed no changes in cytokines TNF-α and IL-1β levels, indicating that ciprofloxacin may play an anti-inflammatory role.

Conclusion

Collectively, apart from the direct antibacterial role of 2Abz²³S²⁹, our data illustrated that 2Abz²³S²⁹ modulates pro-inflammatory cytokine production of bladder in a dose-dependent manner, which has implications for the development of new anti-infective agents.

The immune response to infection in the bladder

The bladder is continuously protected by passive defences such as a mucus layer, antimicrobial peptides and secretory immunoglobulins; however, these defences are occasionally overcome by invading bacteria that can induce a strong host inflammatory response in the bladder. The urothelium and resident immune cells produce additional defence molecules, cytokines and chemokines, which recruit inflammatory cells to the infected tissue. Resident and recruited immune cells act together to eradicate bacteria from the bladder and to develop lasting immune memory against infection. However, urinary tract infection (UTI) is commonly recurrent, suggesting that the induction of a memory response in the bladder is inadequate to prevent reinfection. Additionally, infection seems to induce long-lasting changes in the urothelium, which can render the tissue more susceptible to future infection. The innate immune response is well-studied in the field of UTI, but considerably less is known about how adaptive immunity develops and how repair mechanisms restore bladder homeostasis following infection. Furthermore, data demonstrate that sex-based differences in immunity affect resolution and infection can lead to tissue remodelling in the bladder following resolution of UTI. To combat the rise in antimicrobial resistance, innovative therapeutic approaches to bladder infection are currently in development. Improving our understanding of how the bladder responds to infection will support the development of improved treatments for UTI, particularly for those at risk of recurrent infection.

Advances in Understanding the Human Urinary Microbiome and Its Potential Role in Urinary Tract Infection

Recent advances in the analysis of microbial communities colonizing the human body have identified a resident microbial community in the human urinary tract (UT). Compared to many other microbial niches, the human UT harbors a relatively low biomass. Studies have identified many genera and species that may constitute a core urinary microbiome. However, the contribution of the UT microbiome to urinary tract infection (UTI) and recurrent UTI (rUTI) pathobiology is not yet clearly understood. Evidence suggests that commensal species within the UT and urogenital tract (UGT) microbiomes, such as Lactobacillus crispatus, may act to protect against colonization with uropathogens. However, the mechanisms and fundamental biology of the urinary microbiome-host relationship are not understood. The ability to measure and characterize the urinary microbiome has been enabled through the development of next-generation sequencing and bioinformatic platforms that allow for the unbiased detection of resident microbial DNA. Translating technological advances into clinical insight will require further study of the microbial and genomic ecology of the urinary microbiome in both health and disease. Future diagnostic, prognostic, and therapeutic options for the management of UTI may soon incorporate efforts to measure, restore, and/or preserve the native, healthy ecology of the urinary microbiomes.

Host Cathelicidin Exacerbates Group B Streptococcus Urinary Tract Infection

Group B Streptococcus (GBS) causes frequent urinary tract infection (UTI) in susceptible populations, including individuals with type 2 diabetes and pregnant women; however, specific host factors responsible for increased GBS susceptibility in these populations are not well characterized. Here, we investigate cathelicidin, a cationic antimicrobial peptide, known to be critical for defense during UTI with uropathogenic Escherichia coli (UPEC). We observed a loss of antimicrobial activity of human and mouse cathelicidins against GBS and UPEC in synthetic urine and no evidence for increased cathelicidin resistance in GBS urinary isolates. Furthermore, we found that GBS degrades cathelicidin in a protease-dependent manner. Surprisingly, in a UTI model, cathelicidin-deficient (Camp-/-) mice showed decreased GBS burdens and mast cell recruitment in the bladder compared to levels in wild-type (WT) mice. Pharmacologic inhibition of mast cells reduced GBS burdens and histamine release in WT but not Camp-/- mice. Streptozotocin-induced diabetic mice had increased bladder cathelicidin production and mast cell recruitment at 24 h postinfection with GBS compared to levels in nondiabetic controls. We propose that cathelicidin is an important immune regulator but ineffective antimicrobial peptide against GBS in urine. Combined, our findings may in part explain the increased frequency of GBS UTI in diabetic and pregnant individuals.IMPORTANCE Certain populations such as diabetic individuals are at increased risk for developing urinary tract infections (UTI), although the underlying reasons for this susceptibility are not fully known. Additionally, diabetics are more likely to become infected with certain types of bacteria, such as group B Streptococcus (GBS). In this study, we find that an antimicrobial peptide called cathelicidin, which is thought to protect the bladder from infection, is ineffective in controlling GBS and alters the type of immune cells that migrate to the bladder during infection. Using a mouse model of diabetes, we observe that diabetic mice are more susceptible to GBS infection even though they also have more infiltrating immune cells and increased production of cathelicidin. Taken together, our findings identify this antimicrobial peptide as a potential contributor to increased susceptibility of diabetic individuals to GBS UTI.

The pathogenesis and management of renal scarring in children with vesicoureteric reflux and pyelonephritis

Bacterial urinary tract infections (UTIs) are one of the most common reasons for children to be admitted to hospital. Bacteria infect and invade the bladder (the lower urinary tract) and if the infection disseminates to the upper urinary tract, significant inflammation in the kidneys may arise. Inflammation is a double-edged sword: it is needed to clear bacteria, but if excessive, kidney tissue is injured. During injury, nephrons are destroyed and replaced with deposition of extracellular matrix and a renal scar. In this review, we explore the pathogenesis of UTIs and discuss the risk factors that result in dissemination of bladder infection to the kidneys. Three major risk factors predispose to kidney infections: the presence of vesicoureteric reflux, the presence of bladder and bowel dysfunction, and defects in the ability of the host immune response to clear bacteria. In this review, we will discuss these factors, their relationship to renal scarring, and potential treatments that might be beneficial to prevent renal scar formation in children.

Urinary tract infections: microbial pathogenesis, host-pathogen interactions and new treatment strategies

Urinary tract infections (UTIs) are common, recurrent infections that can be mild to life-threatening. The continued emergence of antibiotic resistance, together with our increasing understanding of the detrimental effects conferred by broad-spectrum antibiotic use on the health of the beneficial microbiota of the host, has underscored the weaknesses in our current treatment paradigm for UTIs. In this Review, we discuss how recent microbiological, structural, genetic and immunological studies have expanded our understanding of host-pathogen interactions during UTI pathogenesis. These basic scientific findings have the potential to shift the strategy for UTI treatment away from broad-spectrum antibiotics targeting conserved aspects of bacterial replication towards pathogen-specific antibiotic-sparing therapeutics that target core determinants of bacterial virulence at the host-pathogen interface.

Rapid Bladder Interleukin-10 Synthesis in Response to Uropathogenic Escherichia coli Is Part of a Defense Strategy Triggered by the Major Bacterial Flagellar Filament FliC and Contingent on TLR5

Interleukin-10 is part of the immune response to urinary tract infection (UTI) due to E. coli, and it is important in the early control of infection in the bladder. Defining the mechanism of engagement of the immune system by the bacteria that enables the protective IL-10 response is critical to exploring how we might exploit this mechanism for new infection control strategies. In this study, we reveal part of the bacterial flagellar apparatus (FliC) is an important component that is sensed by and responsible for induction of IL-10 in the response to UPEC. We show this response occurs in a TLR5-dependent manner. Using infection prevention and control trials in mice infected with E. coli, this study also provides evidence that purified FliC might be of value in novel approaches for the treatment of UTI or in preventing infection by exploiting the FliC-triggered bladder transcriptome.

Urinary tract infection (UTI) caused by uropathogenic Escherichia coli (UPEC) engages interleukin-10 (IL-10) as an early innate immune response to regulate inflammation and promote the control of bladder infection. However, the mechanism of engagement of innate immunity by UPEC that leads to elicitation of IL-10 in the bladder is unknown. Here, we identify the major UPEC flagellar filament, FliC, as a key bacterial component sensed by the bladder innate immune system responsible for the induction of IL-10 synthesis. IL-10 responses of human as well as mouse bladder epithelial cell-monocyte cocultures were triggered by flagella of three major UPEC representative strains, CFT073, UTI89, and EC958. FliC purified to homogeneity induced IL-10 in vitro and in vivo as well as other functionally related cytokines, including IL-6. The genome-wide innate immunological context of FliC-induced IL-10 in the bladder was defined using RNA sequencing that revealed a network of transcriptional and antibacterial defenses comprising 1,400 genes that were induced by FliC. Of the FliC-responsive bladder transcriptome, altered expression of il10 and 808 additional genes were dependent on Toll-like receptor 5 (TLR5), according to analysis of TLR5-deficient mice. Examination of the potential of FliC and associated innate immune signature in the bladder to boost host defense, based on prophylactic or therapeutic administration to mice, revealed significant benefits for the control of UPEC. We conclude that detection of FliC through TLR5 triggers rapid IL-10 synthesis in the bladder, and FliC represents a potential immune modulator that might offer benefit for the treatment or prevention of UPEC UTI.

IMPORTANCE Interleukin-10 is part of the immune response to urinary tract infection (UTI) due to E. coli, and it is important in the early control of infection in the bladder. Defining the mechanism of engagement of the immune system by the bacteria that enables the protective IL-10 response is critical to exploring how we might exploit this mechanism for new infection control strategies. In this study, we reveal part of the bacterial flagellar apparatus (FliC) is an important component that is sensed by and responsible for induction of IL-10 in the response to UPEC. We show this response occurs in a TLR5-dependent manner. Using infection prevention and control trials in mice infected with E. coli, this study also provides evidence that purified FliC might be of value in novel approaches for the treatment of UTI or in preventing infection by exploiting the FliC-triggered bladder transcriptome.

Differential interleukin-1β induction by uropathogenic Escherichia coli correlates with its phylotype and serum C-reactive protein levels in Korean infants

Urinary tract infection (UTI) is one of the most common bacterial infections in infants less than age 1 year. UTIs frequently recur and result in long-term effects include sepsis and renal scarring. Uropathogenic Escherichia coli (UPEC), the most prevalent organism found in UTIs, can cause host inflammation via various virulence factors including hemolysin and cytotoxic necrotizing factors by inducing inflammatory cytokines such as interleukin (IL)-1β. However, the ability of each UPEC organism to induce IL-1β production may differ by strain. Furthermore, the correlation between differential IL-1β induction and its relevance in pathology has not been well studied. In this study, we isolated UPEC from children under age 24 months and infected bone-marrow derived macrophages with the isolates to investigate secretion of IL-1β. We found that children with higher concentrations of C-reactive protein (CRP) were more likely to harbor phylotype B2 UPEC strains that induced more IL-1β production than phylotype D. We also observed a significant correlation between serum CRP level and in vitro IL-1β induction by phylotype B2 UPEC bacteria. Our results highlight the diversity of UPEC in terms of IL-1β induction capacity in macrophages and suggest a potential pathogenic role in UTIs by inducing inflammation in infants.

Mucosal infection rewires TNFɑ signaling dynamics to skew susceptibility to recurrence

A mucosal infectious disease episode can render the host either more or less susceptible to recurrent infection, but the specific mechanisms that tip the balance remain unclear. We investigated this question in a mouse model of recurrent urinary tract infection and found that a prior bladder infection resulted in an earlier onset of tumor necrosis factor-alpha (TNFɑ)-mediated bladder inflammation upon subsequent bacterial challenge, relative to age-matched naive mice. However, the duration of TNFɑ signaling activation differed according to whether the first infection was chronic (Sensitized) or self-limiting (Resolved). TNFɑ depletion studies revealed that transient early-phase TNFɑ signaling in Resolved mice promoted clearance of bladder-colonizing bacteria via rapid recruitment of neutrophils and subsequent exfoliation of infected bladder cells. In contrast, sustained TNFɑ signaling in Sensitized mice prolonged damaging inflammation, worsening infection. This work reveals how TNFɑ signaling dynamics can be rewired by a prior infection to shape diverse susceptibilities to future mucosal infections.

DNA methylation analysis of porcine mammary epithelial cells reveals differentially methylated loci associated with immune response against Escherichia coli challenge

Background

Epigenetic changes such as cytosine (CpG) DNA methylations regulate gene expression patterns in response to environmental cues including infections. Microbial infections induce DNA methylations that play a potential role in modulating host-immune response. In the present study, we sought to determine DNA methylation changes induced by the mastitis causing Escherichia coli (E. coli) in porcine mammary epithelial cells (PMEC). Two time points (3 h and 24 h) were selected based on specific transcriptomic changes during the early and late immune responses, respectively.

Results

DNA methylation analysis revealed 561 and 898 significant (P < 0.01) differentially methylated CpG sites at 3 h and 24 h after E. coli challenge in PMEC respectively. These CpG sites mapped to genes that have functional roles in innate and adaptive immune responses. Significantly, hypomethylated CpG sites were found in the promoter regions of immune response genes such as SDF4, SRXN1, CSF1 and CXCL14. The quantitative transcript estimation indicated higher expression associated with the DNA CpG methylation observed in these immune response genes. Further, E. coli challenge significantly reduced the expression levels of DNMT3a, a subtype of de novo DNA methylation enzyme, in PMEC indicating the probable reason for the hypomethylation observed in the immune response genes.

Conclusions

Our study revealed E. coli infection induced DNA methylation loci in the porcine genome. The differentially methylated CpGs were identified in the regulatory regions of genes that play important role in immune response. These results will help to understand epigenetic mechanisms for immune regulation during coliform mastitis in pigs.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5976-7) contains supplementary material, which is available to authorized users.

Sex differences in IL-17 contribute to chronicity in male versus female urinary tract infection

Sex-based differences influence incidence and outcome of infectious disease. Women have a significantly greater incidence of urinary tract infection (UTI) than men, yet, conversely, male UTI is more persistent with greater associated morbidity. Mechanisms underlying these sex-based differences are unknown, in part due to a lack of experimental models. We optimized a model to transurethrally infect male mice and directly compared UTI in both sexes. Although both sexes were initially equally colonized by uropathogenic E. coli, only male and testosterone-treated female mice remained chronically infected for up to 4 weeks. Female mice had more robust innate responses, including higher IL-17 expression, and increased γδ T cells and group 3 innate lymphoid cells in the bladder following infection. Accordingly, neutralizing IL-17 abolished resolution in female mice, identifying a cytokine pathway necessary for bacterial clearance. Our findings support the concept that sex-based responses to UTI contribute to impaired innate immunity in males and provide a rationale for non-antibiotic-based immune targeting to improve the response to UTI.

Augmentation of Urinary Lactoferrin Enhances Host Innate Immune Clearance of Uropathogenic Escherichia coli

Urinary tract infection (UTI) is a prominent global health care burden. Although UTI is readily treated with antibiotics in healthy adults, complicated cases in immune-compromised individuals and the emerging antibiotic resistance of several uropathogens have accelerated the need for new treatment strategies. Here, we surveyed the composition of urinary exosomes in a mouse model of uropathgenic Escherichia coli (UPEC) UTI to identify specific urinary tract defense constituents for therapeutic development. We found an enrichment of the iron-binding glycoprotein lactoferrin in the urinary exosomes of infected mice. In subsequent in vitro studies, we identified human bladder epithelial cells as a source of lactoferrin during UPEC infection. We further established that exogenous treatment with human lactoferrin (hLf) reduces UPEC epithelial adherence and enhances neutrophil antimicrobial functions including bacterial killing and extracellular trap production. Notably, a single intravesicular dose of hLf drastically reduced bladder bacterial burden and neutrophil infiltration in our murine UTI model. We propose that lactoferrin is an important modulator of innate immune responses in the urinary tract and has potential application in novel therapeutic design for UTI.

Direct Detection of Tissue-Resident Bacteria and Chronic Inflammation in the Bladder Wall of Postmenopausal Women with Recurrent Urinary Tract Infection

Urinary tract infections (UTIs) are the most commonly reported infections in adult women and have high rates of recurrence, especially in postmenopausal women. Recurrent UTI (RUTI) greatly reduces quality of life, places a significant burden on the healthcare system, and contributes to antimicrobial resistance. Because treatment of RUTI by long-term antibiotic therapy is often ineffective or poorly tolerated in elderly women, new therapies must be developed. The molecular basis of RUTI, especially in postmenopausal women, has remained unclear because modeling RUTI in mice is difficult, and human data are limited. Invasion of the urothelium and induction of host inflammation are hypothesized to be key mechanisms by which bacterial pathogens cause RUTI. To further our understanding of RUTI in humans, we performed a systematic analysis of urine and bladder biopsy samples from postmenopausal women undergoing cystoscopy with fulguration of trigonitis in the advanced management of antibiotic-refractory RUTI. We provide direct evidence that bacteria reside in the bladder wall of postmenopausal RUTI patients and that diverse bacterial species can be isolated from the bladder tissue. Histopathological scoring revealed significant edema and alterations of urothelial architecture in RUTI patient biopsies. Lymphocytes, including plasma B-cells, were detected within the mesenchyme, urothelium, and follicular aggregates in the majority of patients, indicating that the local adaptive immune response is active during human RUTI. These data provide conclusive evidence that bacteria invade the human urothelium and suggest that diverse bacterial species and the adaptive immune response play important roles in RUTI in humans.

The Impact of Maternal Microbes and Microbial Colonization in Early Life on Hematopoiesis

All body surfaces are colonized by microbes, which occurs through a dynamic process over the first few years of life. Initial colonizing microbes are transferred from the maternal microbiota to the newborn through vertical transmission. Postnatal maturation of the immune system is heavily influenced by these microbes, particularly during early life. Although microbial-mediated education of the immune system is better understood at mucosal sites, recent data indicate that the systemic immune system is also shaped by the microbiota. Bacterial products and metabolites produced through microbial metabolism can reach distal sites, and metabolites derived from the maternal microbiota can cross the placenta and are present in milk. Recent studies show that the microbiota can even influence immune development in primary lymphoid organs like the bone marrow. This review outlines our current knowledge of how the microbiota can impact hematopoiesis, with a focus on the effects of maternal and early-life microbiota.

Urine Cytokine and Chemokine Levels Predict Urinary Tract Infection Severity Independent of Uropathogen, Urine Bacterial Burden, Host Genetics, and Host Age

Urinary tract infections (UTIs) are among the most common infections worldwide. Diagnosing UTIs in older adults poses a significant challenge as asymptomatic colonization is common. Identification of a noninvasive profile that predicts likelihood of progressing from urine colonization to severe disease would provide a significant advantage in clinical practice. We monitored colonization susceptibility, disease severity, and immune response to two uropathogens in two mouse strains across three age groups to identify predictors of infection outcome. Proteus mirabilis caused more severe disease than Escherichia coli, regardless of mouse strain or age, and was associated with differences in interleukin-1β (IL-1β), beta interferon (IFN-β), CXCL5 (LIX), CCL5 (RANTES), and CCL2 (MCP-1). In a comparison of responses to infection across age groups, mature adult mice were better able to control colonization and prevent progression to kidney colonization and bacteremia than young or aged mice, regardless of mouse strain or bacterial species, and this was associated with differences in IL-23, CXCL1, and CCL5. A bimodal distribution was noted for urine colonization, which was strongly associated with bladder CFU counts and the magnitude of the immune response but independent of age or disease severity. To determine the value of urine cytokine and chemokine levels for predicting severe disease, all infection data sets were combined and subjected to a series of logistic regressions. A multivariate model incorporating IL-1β, CXCL1, and CCL2 had strong predictive value for identifying mice that did not develop kidney colonization or bacteremia, regardless of mouse genetic background, age, infecting bacterial species, or urine bacterial burden. In conclusion, urine cytokine profiles could potentially serve as a noninvasive decision support tool in clinical practice and contribute to antimicrobial stewardship.

Shigella-Induced Emergency Granulopoiesis Protects Zebrafish Larvae from Secondary Infection

Emergency granulopoiesis is a hematopoietic program of stem cell-driven neutrophil production used to counteract immune cell exhaustion following infection. Shigella flexneri is a Gram-negative enteroinvasive pathogen controlled by neutrophils. In this study, we use a Shigella-zebrafish (Danio rerio) infection model to investigate emergency granulopoiesis in vivo. We show that stem cell-driven neutrophil production occurs in response to Shigella infection and requires macrophage-independent signaling by granulocyte colony-stimulating factor (Gcsf). To test whether emergency granulopoiesis can function beyond homoeostasis to enhance innate immunity, we developed a reinfection assay using zebrafish larvae that have not yet developed an adaptive immune system. Strikingly, larvae primed with a sublethal dose of Shigella are protected against a secondary lethal dose of Shigella in a type III secretion system (T3SS)-dependent manner. Collectively, these results highlight a new role for emergency granulopoiesis in boosting host defense and demonstrate that zebrafish larvae can be a valuable in vivo model to investigate innate immune memory.

Shigella is an important human pathogen of the gut. Emergency granulopoiesis is the enhanced production of neutrophils by hematopoietic stem and progenitor cells (HSPCs) upon infection and is widely considered a homoeostatic mechanism for replacing exhausted leukocytes. In this study, we developed a Shigella-zebrafish infection model to investigate stem cell-driven emergency granulopoiesis. We discovered that zebrafish initiate granulopoiesis in response to Shigella infection, via macrophage-independent signaling of granulocyte colony-stimulating factor (Gcsf). Strikingly, larvae primed with a sublethal dose of Shigella are protected against a secondary lethal dose of Shigella in a type III secretion system (T3SS)-dependent manner. Taken together, we show that zebrafish infection can be used to capture Shigella-mediated stem cell-driven granulopoiesis and provide a new model system to study stem cell biology in vivo. Our results also highlight the potential of manipulating stem cell-driven granulopoiesis to boost innate immunity and combat infectious disease.

Bladder resident macrophages: Mucosal sentinels

Macrophages are instrumental in the response to infectious and noninfectious diseases, however, their role in the bladder is poorly understood. Indeed, the bladder is a mucosal tissue frequently overlooked in research, despite the prevalence of illnesses such as urinary tract infection and bladder cancer. Notably, bladder tissue macrophages are among the most populous resident immune cells in this organ and recent studies support that resident macrophages and infiltrating monocytes play nonredundant roles in response to infection, immunotherapy, and inflammation. Advancing our understanding of macrophage behavior in the bladder is complicated by the difficulty in obtaining tissue-resident cells. Surmounting this challenge, however, for a greater understanding of macrophage ontology, impact on innate and adaptive immunity, and regulation of homeostasis, will ultimately contribute to better therapies for common afflictions of the bladder.

Bacterial pathogenesis and interleukin-17: interconnecting mechanisms of immune regulation, host genetics, and microbial virulence that influence severity of infection

Interleukin-17 (IL-17) is a pro-inflammatory cytokine involved in the control of many different disorders, including autoimmune, oncogenic, and diverse infectious diseases. In the context of infectious diseases, IL-17 protects the host against various classes of microorganisms but, intriguingly, can also exacerbate the severity of some infections. The regulation of IL-17 expression stems, in part, from the activity of Interleukin-23 (IL-23), which drives the maturation of different classes of IL-17-producing cells that can alter the course of infection. In this review, we analyze IL-17/IL-23 signalling in bacterial infection, and examine the interconnecting mechanisms that link immune regulation, host genetics, and microbial virulence in the context of bacterial pathogenesis. We consider the roles of IL-17 in both acute and chronic bacterial infections, with a focus on mouse models of human bacterial disease that involve infection of mucosal surfaces in the lungs, urogenital, and gastrointestinal tracts. Polymorphisms in IL-17-encoding genes in humans, which have been associated with heightened host susceptibility to some bacterial pathogens, are discussed. Finally, we examine the implications of IL-17 biology in infectious diseases for the development of novel therapeutic strategies targeted at preventing bacterial infection.

Distinct Signature of Oxylipid Mediators of Inflammation during Infection and Asymptomatic Colonization by E. coli in the Urinary Bladder

Urinary tract infection (UTI) is an extremely common infectious disease. Uropathogenic Escherichia coli (UPEC) is the predominant etiological agent of UTI. Asymptomatic bacteriuric E. coli (ABEC) strains successfully colonize the urinary tract resulting in asymptomatic bacteriuria (ABU) and do not induce symptoms associated with UTI. Oxylipids are key signaling molecules involved in inflammation. Based on the distinct clinical outcomes of E. coli colonization, we hypothesized that UPEC triggers the production of predominantly proinflammatory oxylipids and ABEC leads to production of primarily anti-inflammatory or proresolving oxylipids in the urinary tract. We performed quantitative detection of 39 oxylipid mediators with proinflammatory, anti-inflammatory, and proresolving properties, during UTI and ABU caused by genetically distinct E. coli strains in the murine urinary bladder. Our results reveal that infection with UPEC causes an increased accumulation of proinflammatory oxylipids as early as 6 h postinoculation, compared to controls. To the contrary, ABEC colonization leads to decreased accumulation of proinflammatory oxylipids at the early time point compared to UPEC infection but does not affect the level of proresolving oxylipids. This report represents the first comprehensive investigation on the oxylipidome during benign ABEC colonization observed in ABU and acute inflammation triggered by UPEC leading to UTI.

Urinary Tract Infection in a Small Animal Model: Transurethral Catheterization of Male and Female Mice

Urinary tract infections (UTI) are extremely common worldwide, incurring significant morbidity and healthcare-associated expenses. Small animal models, which accurately reflect disease establishment and progression, permit dissection of host-pathogen interactions and generation of immunity to infection. In mice, intravesical instillation of uropathogenic E. coli, the causative agent in more than 85% of community acquired UTI, recapitulates many of the stages of infection observed in humans. Until recently, however, UTI could only be modeled in female animals. This limitation has hindered the study of sex-related differences in UTI, as well as other bladder pathologies, such as cancer. Here, we describe a method to instill male mice that allows direct comparison between female and male animals and provide a detailed protocol to assess bladder tissue by flow cytometry as a means to better understand host responses to infection. Together, these approaches will aid in the identification of host factors that contribute to sex biases observed in UTI and other bladder-associated diseases.

Enterococcus faecalis Promotes Innate Immune Suppression and Polymicrobial Catheter-Associated Urinary Tract Infection

Enterococcus faecalis, a member of the human gastrointestinal microbiota, is an opportunistic pathogen associated with hospital-acquired wound, bloodstream, and urinary tract infections. E. faecalis can subvert or evade immune-mediated clearance, although the mechanisms are poorly understood. In this study, we examined E. faecalis-mediated subversion of macrophage activation. We observed that E. faecalis actively prevents NF-κB signaling in mouse RAW264.7 macrophages in the presence of Toll-like receptor agonists and during polymicrobial infection with Escherichia coliE. faecalis and E. coli coinfection in a mouse model of catheter-associated urinary tract infection (CAUTI) resulted in a suppressed macrophage transcriptional response in the bladder compared to that with E. coli infection alone. Finally, we demonstrated that coinoculation of E. faecalis with a commensal strain of E. coli into catheterized bladders significantly augmented E. coli CAUTI. Taken together, these results support the hypothesis that E. faecalis suppression of NF-κB-driven responses in macrophages promotes polymicrobial CAUTI pathogenesis, especially during coinfection with less virulent or commensal E. coli strains.

Model systems for the study of Enterococcal colonization and infection

Enterococcus faecalis and Enterococcus faecium are common inhabitants of the human gastrointestinal tract, as well as frequent opportunistic pathogens. Enterococci cause a range of infections including, most frequently, infections of the urinary tract, catheterized urinary tract, bloodstream, wounds and surgical sites, and heart valves in endocarditis. Enterococcal infections are often biofilm-associated, polymicrobial in nature, and resistant to antibiotics of last resort. Understanding Enterococcal mechanisms of colonization and pathogenesis are important for identifying new ways to manage and intervene with these infections. We review vertebrate and invertebrate model systems applied to study the most common E. faecalis and E. faecium infections, with emphasis on recent findings examining Enterococcal-host interactions using these models. We discuss strengths and shortcomings of each model, propose future animal models not yet applied to study mono- and polymicrobial infections involving E. faecalis and E. faecium, and comment on the significance of anti-virulence strategies derived from a fundamental understanding of host-pathogen interactions in model systems.

Male kidney allograft recipients at risk for urinary tract infection?

Background

Urinary tract infection (UTI) is the most common infection after renal transplantation (RTx). Although female sex is a well-known risk factor for the development of UTI after RTx, the role of the donor sex in this context remains unclear.

Methods

In this case control study 6,763 RTx cases were screened for UTI when presenting at our transplant outpatient clinics. 102 different RTx patients fulfilled the inclusion criteria and were compared to 102 controls. Data on renal function was prospectively followed for 12 months. Results were compared to a previous RTx cohort from our transplant center. Additionally, we assessed the immunological response of leukocytes from 58 kidney recipients and 16 controls to lipopolysaccharide stimulation.

Result

After identification by univariate analysis, multivariate logistic regression analysis indicated female sex, minor height, advanced age and male kidney allograft sex to be associated with the occurrence of UTI after RTx. Female recipients who received male grafts had the best renal function 12 months after presentation. However, leukocyte response of recipients to lipopolysaccharide was impaired irrespective of donor and recipient sex to the same extend.

Conclusions

We conclude from our data that male kidney allografts are associated with the occurrence of UTI after RTx but did not influence the response of leukocytes to lipopolysaccharide. Further prospective studies are needed to identify the underlying mechanisms of higher male kidney donor dependent UTI.

Vitamin D-deficient mice have more invasive urinary tract infection

Vitamin D deficiency is a common health problem with consequences not limited to bone and calcium hemostasis. Low levels have also been linked to tuberculosis and other respiratory infections as well as autoimmune diseases. We have previously shown that supplementation with vitamin D can induce the antimicrobial peptide cathelicidin during ex vivo infection of human urinary bladder. In rodents, however, cathelicidin expression is not linked to vitamin D and therefore this vitamin D-related effect fighting bacterial invasion is not relevant. To determine if vitamin D had further protective mechanisms during urinary tract infections, we therefore used a mouse model. In vitamin D-deficient mice, we detected more intracellular bacterial communities in the urinary bladder, higher degree of bacterial spread to the upper urinary tract and a skewed cytokine response. Furthermore, we show that the vitamin D receptor was upregulated in the urinary bladder and translocated into the cell nucleus after E. coli infection. This study supports a more general role for vitamin D as a local immune response mediator in the urinary tract.

Urothelial generation and regeneration in development, injury, and cancer

Homeostatic maintenance and repair of the urothelium upon injury are required for a functional bladder in both healthy and disease conditions. Understanding the cellular and molecular mechanisms underlying the urothelial regenerative response is key to designing strategies for tissue repair and ultimately treatments for urologic diseases including urinary tract infections, voiding dysfunction, painful bladder syndrome, and bladder cancer. In this article, we review studies on urothelial ontogeny during development and regeneration following various injury modalities. Signaling pathways involved in urothelial regeneration and in urothelial carcinogenesis are also discussed. Developmental Dynamics 246:336-343, 2017. © 2016 Wiley Periodicals, Inc.

The cytochrome bd-I respiratory oxidase augments survival of multidrug-resistant Escherichia coli during infection

Nitric oxide (NO) is a toxic free radical produced by neutrophils and macrophages in response to infection. Uropathogenic Escherichia coli (UPEC) induces a variety of defence mechanisms in response to NO, including direct NO detoxification (Hmp, NorVW, NrfA), iron-sulphur cluster repair (YtfE), and the expression of the NO-tolerant cytochrome bd-I respiratory oxidase (CydAB). The current study quantifies the relative contribution of these systems to UPEC growth and survival during infection. Loss of the flavohemoglobin Hmp and cytochrome bd-I elicit the greatest sensitivity to NO-mediated growth inhibition, whereas all but the periplasmic nitrite reductase NrfA provide protection against neutrophil killing and promote survival within activated macrophages. Intriguingly, the cytochrome bd-I respiratory oxidase was the only system that augmented UPEC survival in a mouse model after 2 days, suggesting that maintaining aerobic respiration under conditions of nitrosative stress is a key factor for host colonisation. These findings suggest that while UPEC have acquired a host of specialized mechanisms to evade nitrosative stresses, the cytochrome bd-I respiratory oxidase is the main contributor to NO tolerance and host colonisation under microaerobic conditions. This respiratory complex is therefore of major importance for the accumulation of high bacterial loads during infection of the urinary tract.

Urinary Tract Infection: Pathogenesis and Outlook

The clinical syndromes comprising urinary tract infection (UTI) continue to exert significant impact on millions of patients worldwide, most of whom are otherwise healthy women. Antibiotic therapy for acute cystitis does not prevent recurrences, which plague up to one fourth of women after an initial UTI. Rising antimicrobial resistance among uropathogenic bacteria further complicates therapeutic decisions, necessitating new approaches based on fundamental biological investigation. In this review, we highlight contemporary advances in the field of UTI pathogenesis and how these might inform both our clinical perspective and future scientific priorities.