Host Cathelicidin Exacerbates Group B Streptococcus Urinary Tract Infection

Re-framing the importance of Group B Streptococcus as a gut-resident pathobiont

Streptococcus agalactiae (Group B Streptococcus, GBS) is a Gram-positive bacterial species that causes disease in humans across the lifespan. While antibiotics are used to mitigate GBS infections, it is evident that antibiotics disrupt human microbiomes (which can predispose people to other diseases later in life), and antibiotic resistance in GBS is on the rise. Taken together, these unintended negative impacts of antibiotics highlight the need for precision approaches for minimizing GBS disease. One possible approach involves selectively depleting GBS in its commensal niches before it can cause disease at other body sites or be transmitted to at-risk individuals. One understudied commensal niche of GBS is the adult gastrointestinal (GI) tract, which may predispose colonization at other body sites in individuals at risk for GBS disease. However, a better understanding of the host-, microbiome-, and GBS-determined variables that dictate GBS GI carriage is needed before precise GI decolonization approaches can be developed. In this review, we synthesize current knowledge of the diverse body sites occupied by GBS as a pathogen and as a commensal. We summarize key molecular factors GBS utilizes to colonize different host-associated niches to inform future efforts to study GBS in the GI tract. We also discuss other GI commensals that are pathogenic in other body sites to emphasize the broader utility of precise de-colonization approaches for mitigating infections by GBS and other bacterial pathogens. Finally, we highlight how GBS treatments could be improved with a more holistic understanding of GBS enabled by continued GI-focused study.

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.

In silico and experimental analysis of the repeated domains in BvaP, a protein important for GBS vaginal colonization

Streptococcus agalactiae (group B strep, GBS) infections in neonates are often fatal and strongly associated with maternal GBS vaginal colonization. Previously, we highlighted the importance of a formerly uncharacterized protein, BvaP, in GBS vaginal colonization. BvaP is highly conserved across GBS and is made up of repeated domains, with a variable number of repeats between strains. Here, we evaluate the prevalence of BvaP repeated domains and their relevance in phenotypes previously associated with vaginal colonization. Using in silico analysis, we found that the number of repeats in the BvaP protein does not generally appear to be associated with serotype, isolation site, or host. Using BvaP truncations in GBS strain A909, we determined that a smaller number of repeats was correlated with decreased bacterial chain length, but adherence to vaginal epithelial cells was complemented using BvaP containing one, two, three, or five repeats. Future research will be geared toward understanding the host immune response to BvaP in vivo and whether vaginal carriage or host response is dependent on the BvaP repeated domains.

Interspecies Interactions within the Host: the Social Network of Group B Streptococcus

Group B Streptococcus (GBS) is a pervasive neonatal pathogen accounting for a combined half a million deaths and stillbirths annually. The most common source of fetal or neonatal GBS exposure is the maternal microbiota. GBS asymptomatically colonizes the gastrointestinal and vaginal mucosa of 1 in 5 individuals globally, although its precise role in these niches is not well understood. To prevent vertical transmission, broad-spectrum antibiotics are administered to GBS-positive mothers during labor in many countries. Although antibiotics have significantly reduced GBS early-onset neonatal disease, there are several unintended consequences, including an altered neonatal microbiota and increased risk for other microbial infections. Additionally, the incidence of late-onset GBS neonatal disease remains unaffected and has sparked an emerging hypothesis that GBS-microbe interactions in developing neonatal gut microbiota may be directly involved in this disease process. This review summarizes our current understanding of GBS interactions with other resident microbes at the mucosal surface from multiple angles, including clinical association studies, agriculture and aquaculture observations, and experimental animal model systems. We also include a comprehensive review of in vitro findings of GBS interactions with other bacterial and fungal microbes, both commensal and pathogenic, along with newly established animal models of GBS vaginal colonization and in utero or neonatal infection. Finally, we provide a perspective on emerging areas of research and current strategies to design microbe-targeting prebiotic or probiotic therapeutic intervention strategies to prevent GBS disease in vulnerable populations.

Enhanced Vulnerability of Diabetic Mice to Hypervirulent Streptococcus agalactiae ST-17 Infection

Streptococcus agalactiae (Group B Streptococcus, GBS) is the leading cause of neonatal sepsis and meningitis but has been recently isolated from non-pregnant adults with underlying medical conditions like diabetes. Despite diabetes being a key risk factor for invasive disease, the pathological consequences during GBS infection remain poorly characterized. Here, we demonstrate the pathogenicity of the GBS90356-ST17 and COH1-ST17 strains in streptozotocin-induced diabetic mice. We show that GBS can spread through the bloodstream and colonize several tissues, presenting a higher bacterial count in diabetic-infected mice when compared to non-diabetic-infected mice. Histological sections of the lungs showed inflammatory cell infiltration, collapsed septa, and red blood cell extravasation in the diabetic-infected group. A significant increase in collagen deposition and elastic fibers were also observed in the lungs. Moreover, the diabetic group presented red blood cells that adhered to the valve wall and disorganized cardiac muscle fibers. An increased expression of KC protein, IL-1β, genes encoding immune cell markers, and ROS (reactive oxygen species) production was observed in diabetic-infected mice, suggesting GBS promotes high levels of inflammation when compared to non-diabetic animals. Our data indicate that efforts to reverse the epidemic of diabetes could considerably reduce the incidence of invasive infection, morbidity and mortality due to GBS.

In Vivo Role of Two-Component Regulatory Systems in Models of Urinary Tract Infections

Two-component signaling systems (TCSs) are finely regulated mechanisms by which bacteria adapt to environmental conditions by modifying the expression of target genes. In bacterial pathogenesis, TCSs play important roles in modulating adhesion to mucosal surfaces, resistance to antibiotics, and metabolic adaptation. In the context of urinary tract infections (UTI), one of the most common types infections causing significant health problems worldwide, uropathogens use TCSs for adaptation, survival, and establishment of pathogenicity. For example, uropathogens can exploit TCSs to survive inside bladder epithelial cells, sense osmolar variations in urine, promote their ascension along the urinary tract or even produce lytic enzymes resulting in exfoliation of the urothelium. Despite the usefulness of studying the function of TCSs in in vitro experimental models, it is of primary necessity to study bacterial gene regulation also in the context of host niches, each displaying its own biological, chemical, and physical features. In light of this, the aim of this review is to provide a concise description of several bacterial TCSs, whose activity has been described in mouse models of 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.

Phage Resistance Accompanies Reduced Fitness of Uropathogenic Escherichia coli in the Urinary Environment

Urinary tract infection (UTI) is among the most common infections treated worldwide each year and is caused primarily by uropathogenic Escherichia coli (UPEC). Rising rates of antibiotic resistance among uropathogens have spurred a consideration of alternative treatment strategies, such as bacteriophage (phage) therapy; however, phage-bacterial interactions within the urinary environment are poorly defined. Here, we assess the activity of two phages, namely, HP3 and ES17, against clinical UPEC isolates using in vitro and in vivo models of UTI. In both bacteriologic medium and pooled human urine, we identified phage resistance arising within the first 6 to 8 h of coincubation. Whole-genome sequencing revealed that UPEC strains resistant to HP3 and ES17 harbored mutations in genes involved in lipopolysaccharide (LPS) biosynthesis. Phage-resistant strains displayed several in vitro phenotypes, including alterations to adherence to and invasion of human bladder epithelial HTB-9 cells and increased biofilm formation in some isolates. Interestingly, these phage-resistant UPEC isolates demonstrated reduced growth in pooled human urine, which could be partially rescued by nutrient supplementation and were more sensitive to several outer membrane-targeting antibiotics than parental strains. Additionally, phage-resistant UPEC isolates were attenuated in bladder colonization in a murine UTI model. In total, our findings suggest that while resistance to phages, such as HP3 and ES17, may arise readily in the urinary environment, phage resistance is accompanied by fitness costs which may render UPEC more susceptible to host immunity or antibiotics.

IMPORTANCE UTI is one of the most common causes of outpatient antibiotic use, and rising antibiotic resistance threatens the ability to control UTI unless alternative treatments are developed. Bacteriophage (phage) therapy is gaining renewed interest; however, much like with antibiotics, bacteria can readily become resistant to phages. For successful UTI treatment, we must predict how bacteria will evade killing by phage and identify the downstream consequences of phage resistance during bacterial infection. In our current study, we found that while phage-resistant bacteria quickly emerged in vitro, these bacteria were less capable of growing in human urine and colonizing the murine bladder. These results suggest that phage therapy poses a viable UTI treatment if phage resistance confers fitness costs for the uropathogen. These results have implications for developing cocktails of phage with multiple different bacterial targets, of which each is evaded only at the cost of bacterial fitness.

Human Milk Oligosaccharides Reduce Murine Group B Streptococcus Vaginal Colonization with Minimal Impact on the Vaginal Microbiota

Group B Streptococcus (GBS) colonizes the vaginal mucosa of a significant percentage of healthy women and is a leading cause of neonatal bacterial infections. Currently, pregnant women are screened in the last month of pregnancy, and GBS-positive women are given antibiotics during parturition to prevent bacterial transmission to the neonate. Recently, human milk oligosaccharides (HMOs) isolated from breastmilk were found to inhibit GBS growth and biofilm formation in vitro, and women that make certain HMOs are less likely to be vaginally colonized with GBS. Using in vitro human vaginal epithelial cells and a murine vaginal colonization model, we tested the impact of HMO treatment on GBS burdens and the composition of the endogenous microbiota by 16S rRNA amplicon sequencing. HMO treatment reduced GBS vaginal burdens in vivo with minimal alterations to the vaginal microbiota. HMOs displayed potent inhibitory activity against GBS in vitro, but HMO pretreatment did not alter adherence of GBS or the probiotic Lactobacillus rhamnosus to human vaginal epithelial cells. In addition, disruption of a putative GBS glycosyltransferase (Δsan_0913) rendered the bacterium largely resistant to HMO inhibition in vitro and in vivo but did not compromise its adherence, colonization, or biofilm formation in the absence of HMOs. We conclude that HMOs are a promising therapeutic bioactive to limit GBS vaginal colonization with minimal impacts on the vaginal microenvironment.

IMPORTANCE During pregnancy, GBS ascension into the uterus can cause fetal infection or preterm birth. In addition, GBS exposure during labor creates a risk of serious disease in the vulnerable newborn and mother postpartum. Current recommended prophylaxis consists of administering broad-spectrum antibiotics to GBS-positive mothers during labor. Although antibiotics have significantly reduced GBS neonatal disease, there are several unintended consequences, including altered neonatal gut bacteria and increased risk for other types of infection. Innovative preventions displaying more targeted antimicrobial activity, while leaving the maternal microbiota intact, are thus appealing. Using a mouse model, we found that human milk oligosaccharides (HMOs) reduce GBS burdens without perturbing the vaginal microbiota. We conclude that HMOs are a promising alternative to antibiotics to reduce GBS neonatal disease.

Group B streptococcal infection of the genitourinary tract in pregnant and non-pregnant patients with diabetes mellitus: An immunocompromised host or something more?

Group B Streptococcus (GBS), also known as Streptococcus agalactiae is a Gram-positive bacterium commonly encountered as part of the microbiota within the human gastrointestinal tract. A common cause of infections during pregnancy, GBS is responsible for invasive diseases ranging from urinary tract infections to chorioamnionitis and neonatal sepsis. Diabetes mellitus (DM) is a chronic disease resulting from impaired regulation of blood glucose levels. The incidence of DM has steadily increased worldwide to affecting over 450 million people. Poorly controlled DM is associated with multiple health comorbidities including an increased risk for infection. Epidemiologic studies have clearly demonstrated that DM correlates with an increased risk for invasive GBS infections, including skin and soft tissue infections and sepsis in non-pregnant adults. However, the impact of DM on risk for invasive GBS urogenital infections, particularly during the already vulnerable time of pregnancy, is less clear. We review the evolving epidemiology, immunology, and pathophysiology of GBS urogenital infections including rectovaginal colonization during pregnancy, neonatal infections of infants exposed to DM in utero, and urinary tract infections in pregnant and non-pregnant adults in the context of DM and highlight in vitro studies examining why DM might increase risk for GBS urogenital infection.

Hemolytic activity and biofilm-formation among clinical isolates of group B streptococcus causing acute urinary tract infection and asymptomatic bacteriuria

Streptococcus agalactiae, also known as group B Streptococcus, is an aetiological agent of urinary tract infection (UTI) in adults, including cystitis, pyelonephritis and asymptomatic bacteriuria (ABU). Whereas ABU-causing S. agalactiae (ABSA) have been shown to grow and achieve higher culture denstity in human urine compared to uropathogenic S. agalactiae (UPSA) other phenotypic distinctions between S. agalactiae isolated from different forms of UTI are not known. Here, we define the hemolytic activities and biofilm-formation of a collection of clinical isolates of UPSA, ABSA and recurrent S. agalactiae bacteriuria (rSAB) strains to explore these phenotypes in the context of clinical history of isolates. A total of 61 UPSA, 184 ABSA, and 47 rSAB isolates were analyzed for relative hemolytic activity by spot assay on blood agar, which was validated using a erythrocyte lysis suspension assay. Biofilm formation was determined by microtiter plate assay with Lysogeny and Todd-Hewitt broths supplemented with 1% glucose to induce biofilm formation. We also used multiplex PCR to analyze isolates for the presence of genes encoding adhesive pili, which contribute to biofilm formation. Comparing the hemolytic activities of 292 isolates showed, surprisingly, that ABSA strains were significantly more likely to be highly hemolytic compared to other strains. In contrast, there were no differences between the relative abilities of strains from the different clinical history groups to form biofilms. Taken together, these findings demonstrate a propensity of S. agalactiae causing ABU to be highly hemolytic but no link between clinical history of UTI strains and ability to form biofilm.

Recurrent Urinary Tract Infection: A Mystery in Search of Better Model Systems

Urinary tract infections (UTIs) are among the most common infectious diseases worldwide but are significantly understudied. Uropathogenic E. coli (UPEC) accounts for a significant proportion of UTI, but a large number of other species can infect the urinary tract, each of which will have unique host-pathogen interactions with the bladder environment. Given the substantial economic burden of UTI and its increasing antibiotic resistance, there is an urgent need to better understand UTI pathophysiology - especially its tendency to relapse and recur. Most models developed to date use murine infection; few human-relevant models exist. Of these, the majority of in vitro UTI models have utilized cells in static culture, but UTI needs to be studied in the context of the unique aspects of the bladder's biophysical environment (e.g., tissue architecture, urine, fluid flow, and stretch). In this review, we summarize the complexities of recurrent UTI, critically assess current infection models and discuss potential improvements. More advanced human cell-based in vitro models have the potential to enable a better understanding of the etiology of UTI disease and to provide a complementary platform alongside animals for drug screening and the search for better treatments.

Streptococcus pyogenes upregulates arginine catabolism to exert its pathogenesis on the skin surface

The arginine deiminase (ADI) pathway has been found in many kinds of bacteria and functions to supplement energy production and provide protection against acid stress. The Streptococcus pyogenes ADI pathway is upregulated upon exposure to various environmental stresses, including glucose starvation. However, there are several unclear points about the advantages to the organism for upregulating arginine catabolism. We show that the ADI pathway contributes to bacterial viability and pathogenesis under low-glucose conditions. S. pyogenes changes global gene expression, including upregulation of virulence genes, by catabolizing arginine. In a murine model of epicutaneous infection, S. pyogenes uses the ADI pathway to augment its pathogenicity by increasing the expression of virulence genes, including those encoding the exotoxins. We also find that arginine from stratum-corneum-derived filaggrin is a key substrate for the ADI pathway. In summary, arginine is a nutrient source that promotes the pathogenicity of S. pyogenes on the skin.

Novel Models of Streptococcus canis Colonization and Disease Reveal Modest Contributions of M-Like (SCM) Protein

Streptococcus canis is a common colonizing bacterium of the urogenital tract of cats and dogs that can also cause invasive disease in these animal populations and in humans. Although the virulence mechanisms of S. canis are not well-characterized, an M-like protein, SCM, has recently identified been as a potential virulence factor. SCM is a surface-associated protein that binds to host plasminogen and IgGs suggesting its possible importance in host-pathogen interactions. In this study, we developed in vitro and ex vivo blood component models and murine models of S. canis vaginal colonization, systemic infection, and dermal infection to compare the virulence potential of the zoonotic S. canis vaginal isolate G361 and its isogenic SCM-deficient mutant (G361∆scm). We found that while S. canis establishes vaginal colonization and causes invasive disease in vivo, the contribution of the SCM protein to virulence phenotypes in these models is modest. We conclude that SCM is dispensable for invasive disease in murine models and for resistance to human blood components ex vivo, but may contribute to mucosal persistence, highlighting a potential contribution to the recently appreciated genetic diversity of SCM across strains and hosts.

Exposure to Moderate Glycosuria Induces Virulence of Group B Streptococcus

To explore whether glycosuria induces virulence of uropathogens, in turn facilitating urinary tract infection (UTI), we exposed group B Streptococcus (GBS) strain 10/84 to human urine plain or with 300 mg/dL glucose (mimicking moderate glycosuria). Exposure to moderate glycosuria significantly augmented bacterial growth, kidney bacterial burden in a mouse model of ascending UTI, and virulence characteristics and expression of corresponding genes. Exposure to glycosuria increased GBS adherence to human bladder epithelial cell line and expression of corresponding PI2a fimbrial gene, antimicrobial peptide LL-37 resistance and bacterial surface charge modulating dltA, and GBS hemolytic ability and expression of genes encoding pore-forming toxins.