Genetic factors in host resistance to urinary tract infection

A bladder blueprint to build better models for understanding homeostasis and disease

The bladder is a complex organ that can be affected by various pathologies, such as cancer or infection. It has a specific tissue structure composed of many different cell types and layers, including urothelial and endothelial cells but also a muscle layer controlling stretch and contraction to void urine. The bladder has constitutive and induced immune responses to infection or damage and harbours a microbiome. Each of these features can be influenced by factors including age and biological sex, which makes modelling homeostasis and disease in the bladder complex and challenging. To model diseases that affect the bladder, mouse models are an invaluable tool to understand the bladder in situ. However, stark differences exist between mice and humans, and so mouse models of human disease have limitations. Thus, models that more closely approximate human physiology would be expected to contribute to improved understanding of bladder biology. As technology advances, improvements in model development and creation of 3D bladder structures are enabling scientists to recapitulate essential aspects of human bladder physiology to gain increased understanding of bladder homeostasis and diseases.

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.

Obesity and recurrent urinary tract infections in premenopausal women: a retrospective study

OBJECTIVES

Studies on the association between obesity and the risk of urinary tract infection (UTI) show inconsistent results. The aim of this study was to determine whether there is any association between obesity and recurrent UTIs (RUTIs) among premenopausal women.

METHODS

A retrospective case-control study was conducted in the outpatient clinics of the internal medicine departments of three hospitals. All consecutive non-pregnant premenopausal women aged 20-55 years, who presented with RUTIs over a 2-year period, were included; these women were compared to randomly selected women from the same outpatient clinics who had no history of RUTI and were age-matched ±5 years. RUTI was defined as a symptomatic UTI that followed the resolution of a previous UTI, or three or more symptomatic episodes over a 12-month period.

RESULTS

Six hundred and ninety-one premenopausal women with UTI were evaluated during the study period. A total 122 of 162 subjects with RUTIs were included in this study and compared to 122 control cases without a history of RUTI. The overall prevalence of RUTIs among the premenopausal women with UTI was 23.4% (162/691). Approximately half of those with RUTIs were obese. The mean age of women with RUTIs was 43.8±9 vs. 40±10 years among the controls (p=0.839). The mean body mass index of women with RUTIs was significantly higher than that of controls: 35±4 vs. 26±3kg/m(2) (p<0.001). Multivariate regression analysis showed that obesity was associated with RUTIs in premenopausal women (odds ratio 4.00, 95% confidence interval 3.2-4.61; p=0.001).

CONCLUSIONS

Obesity was found to be associated with RUTIs in premenopausal women.

Impact of host age and parity on susceptibility to severe urinary tract infection in a murine model

The epidemiology and bacteriology of urinary tract infection (UTI) varies across the human lifespan, but the reasons for these differences are poorly understood. Using established monomicrobial and polymicrobial murine UTI models caused by uropathogenic Escherichia coli (UPEC) and/or Group B Streptococcus (GBS), we demonstrate age and parity as inter-related factors contributing to UTI susceptibility. Young nulliparous animals exhibited 10–100-fold higher bacterial titers compared to older animals. In contrast, multiparity was associated with more severe acute cystitis in older animals compared to age-matched nulliparous controls, particularly in the context of polymicrobial infection where UPEC titers were ∼1000-fold higher in the multiparous compared to the nulliparous host. Multiparity was also associated with significantly increased risk of chronic high titer UPEC cystitis and ascending pyelonephritis. Further evidence is provided that the increased UPEC load in multiparous animals required TLR4-signaling. Together, these data strongly suggest that the experience of childbearing fundamentally and permanently changes the urinary tract and its response to pathogens in a manner that increases susceptibility to severe UTI. Moreover, this murine model provides a system for dissecting these and other lifespan-associated risk factors contributing to severe UTI in at-risk groups.

The association between serum levels of vitamin D and recurrent urinary tract infections in premenopausal women

OBJECTIVES

To examine whether there is any association between serum levels of 25-hydroxy vitamin D (25(OH) vitamin D) and the recurrence of urinary tract infections (UTIs) among premenopausal women.

METHODS

During a period of 3 years, 93 premenopausal women with a medical history of recurrent UTIs were enrolled from the Infectious Diseases Unit. Cases with recurrent UTIs were compared to 93 age-matched (±5 years) women with no history of recurrent UTI (control group), in terms of serum 25(OH) vitamin D and different risk factors for recurrent UTI. Recurrent UTI was defined as three or more episodes of UTI over a 12-month period.

RESULTS

The mean age of women with recurrent UTIs was 43.8±9 years and of controls was 39±10 years (p=0.839). The mean serum levels of 25(OH) vitamin D among women with recurrent UTIs were significantly lower than those of controls (9.8 ng/ml±4 vs. 23 ng/ml±6; p<0.001). Multivariate analysis showed that a serum 25(OH) vitamin D level of <15 ng/ml (odds ratio 4.00, 95% confidence interval 3.40-4.62; p=0.001) was associated with recurrent UTIs in premenopausal women.

CONCLUSIONS

In this retrospective study, we found that recurrent UTIs in premenopausal women are associated with vitamin D deficiency.

Interplay between vesicoureteric reflux and kidney infection in the development of reflux nephropathy in mice

Vesicoureteric reflux (VUR) is a common congenital defect of the urinary tract that is usually discovered after a child develops a urinary tract infection. It is associated with reflux nephropathy, a renal lesion characterized by the presence of chronic tubulointersitial inflammation and fibrosis. Most patients are diagnosed with reflux nephropathy after one or more febrile urinary tract infections, suggesting a potential role for infection in its development. We have recently shown that the C3H mouse has a 100% incidence of VUR. Here, we evaluate the roles of VUR and uropathogenic Escherichia coli infection in the development of reflux nephropathy in the C3H mouse. We find that VUR in combination with sustained kidney infection is crucial to the development of reflux nephropathy, whereas sterile reflux alone fails to induce reflux nephropathy. A single bout of kidney infection without reflux fails to induce reflux nephropathy. The host immune response to infection was examined in two refluxing C3H substrains, HeN and HeJ. HeJ mice, which have a defect in innate immunity and bacterial clearance, demonstrate more significant renal inflammation and reflux nephropathy compared with HeN mice. These studies demonstrate the crucial synergy between VUR, sustained kidney infection and the host immune response in the development of reflux nephropathy in a mouse model of VUR.

Susceptibility to acute pyelonephritis or asymptomatic bacteriuria: host-pathogen interaction in urinary tract infections

Our knowledge of the molecular mechanisms of urinary tract infection (UTI) pathogenesis has advanced greatly in recent years. In this review, we provide a general background of UTI pathogenesis, followed by an update on the mechanisms of UTI susceptibility, with a particular focus on genetic variation affecting innate immunity. The innate immune response of the host is critically important in the antibacterial defence mechanisms of the urinary tract, and bacterial clearance normally proceeds without sequelae. However, slight dysfunctions in these mechanisms may result in acute disease and tissue destruction. The symptoms of acute pyelonephritis are caused by the innate immune response, and inflammation in the urinary tract decreases renal tubular function and may give rise to renal scarring, especially in paediatric patients. In contrast, in children with asymptomatic bacteriuria (ABU), bacteria persist without causing symptoms or pathology. Pathogenic agents trigger a response determined by their virulence factors, mediating adherence to the urinary tract mucosa, signalling through Toll-like receptors (TLRs) and activating the defence mechanisms. In ABU strains, such virulence factors are mostly not expressed. However, the influence of the host on UTI severity cannot be overestimated, and rapid progress is being made in clarifying host susceptibility mechanisms. For example, genetic alterations that reduce TLR4 function are associated with ABU, while polymorphisms reducing IRF3 or CXCR1 expression are associated with acute pyelonephritis and an increased risk for renal scarring. It should be plausible to "individualize" diagnosis and therapy by combining information on bacterial virulence and the host response.

The toll interleukin-1 receptor (IL-1R) 8/single Ig domain IL-1R-related molecule modulates the renal response to bacterial infection

Our immune system has to constantly strike a balance between activation and inhibition of an inflammatory response to combat invading pathogens and avoid inflammation-induced collateral tissue damage. Toll interleukin-1 receptor 8 (IL-1R-8)/single Ig domain IL-1R-related molecule (TIR8/SIGIRR) is an inhibitor of Toll-like receptor (TLR)/IL-1R signaling, which is predominantly expressed in the kidney. The biological role of renal TIR8 during infection is, however, unknown. We therefore evaluated renal TIR8 expression during Escherichia coli pyelonephritis and explored its role in host defense using TIR8(-/-) versus TIR8(+/+) mice. We found that TIR8 protein is abundantly present in the majority of cortical tubular epithelial cells. Pyelonephritis resulted in a significant downregulation of TIR8 mRNA in kidneys of TIR8(+/+) mice. TIR8 inhibited an effective host response against E. coli, as indicated by diminished renal bacterial outgrowth and dysfunction in TIR8(-/-) mice. This correlated with increased amounts of circulating and intrarenal neutrophils at the early phase of infection. TIR8(-/-) tubular epithelial cells had increased cytokine/chemokine production when stimulated with lipopolysaccharide (LPS) or heat-killed E. coli, suggesting that TIR8 played an anti-inflammatory role during pathogen stimulation by inhibiting LPS signaling. These data suggest that TIR8 is an important negative regulator of an LPS-mediated inflammatory response in tubular epithelial cells and dampens an effective antibacterial host response during pyelonephritis caused by uropathogenic E. coli.

Assessment of Toll-like receptor-4 gene polymorphism on pyelonephritis and renal scar

The aim of this study was to evaluate the effect of the TLR-4 gene TLR4 c.896A < G polymorphism on the development and clinical severity of urinary tract infections (UTI) and renal scar formations in children. The patients with first diagnosis of UTI (n = 112) and healthy controls (n = 93) were enrolled in the study. The TLR4 c.896A < G polymorphism was analysed in groups. The mean age of the patients in the study group was 8.1 ± 3.5 years and 9.2 ± 2.7 years for those in the control group. The TLR4 c.896A < G polymorphism was detected in 12.5% in the UTI group and in 15.1% of the control group. Forty patients showed pyelonephritis (PN) with scar tissue, 37 patients had PN without scars, and 35 patients had lower UTI. The TLR4 c.896A < G polymorphism was found in 22.5% of patients with scar-positive PN, and it was also present in 10.8% of patients with scar-negative PN and 2.9% of patients with lower UTI. We found higher TLR4 c.896A < G polymorphism and allelic frequency in patients with upper UTI compared to patients with lower UTI (P = 0.041 and P = 0.039, respectively). No significant difference was observed between patients and the control group for TLR-4 c.896A3. The TLR4 c.896A < G polymorphism and alleles were higher in patients with upper UTI than in patients with lower UTI. The TLR4 c.896A < G polymorphism frequency was nearly twice that in the scar-positive PN patients when compared to the scar-negative patients. Larger-scale studies involving larger numbers of patients should be performed.

Genetics of innate immunity and UTI susceptibility

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

Early severe inflammatory responses to uropathogenic E. coli predispose to chronic and recurrent urinary tract infection

Chronic infections are an increasing problem due to the aging population and the increase in antibiotic resistant organisms. Therefore, understanding the host-pathogen interactions that result in chronic infection is of great importance. Here, we investigate the molecular basis of chronic bacterial cystitis. We establish that introduction of uropathogenic E. coli (UPEC) into the bladders of C3H mice results in two distinct disease outcomes: resolution of acute infection or development of chronic cystitis lasting months. The incidence of chronic cystitis is both host strain and infectious dose-dependent. Further, development of chronic cystitis is preceded by biomarkers of local and systemic acute inflammation at 24 hours post-infection, including severe pyuria and bladder inflammation with mucosal injury, and a distinct serum cytokine signature consisting of elevated IL-5, IL-6, G-CSF, and the IL-8 analog KC. Mice deficient in TLR4 signaling or lymphocytes lack these innate responses and are resistant, to varying degrees, to developing chronic cystitis. Treatment of C3H mice with the glucocorticoid anti-inflammatory drug dexamethasone prior to UPEC infection also suppresses the development of chronic cystitis. Finally, individuals with a history of chronic cystitis, lasting at least 14 days, are significantly more susceptible to redeveloping severe, chronic cystitis upon bacterial challenge. Thus, we have discovered that the development of chronic cystitis in C3H mice by UPEC is facilitated by severe acute inflammatory responses early in infection, which subsequently are predisposing to recurrent cystitis, an insidious problem in women. Overall, these results have significant implications for our understanding of how early host-pathogen interactions at the mucosal surface determines the fate of disease.

Toll-like receptor 4 promoter polymorphisms: common TLR4 variants may protect against severe urinary tract infection

Background

Polymorphisms affecting Toll-like receptor (TLR) structure appear to be rare, as would be expected due to their essential coordinator role in innate immunity. Here, we assess variation in TLR4 expression, rather than structure, as a mechanism to diversify innate immune responses.

Methodology/Principal Findings

We sequenced the TLR4 promoter (4,3 kb) in Swedish blood donors. Since TLR4 plays a vital role in susceptibility to urinary tract infection (UTI), promoter sequences were obtained from children with mild or severe disease. We performed a case-control study of pediatric patients with asymptomatic bacteriuria (ABU) or those prone to recurrent acute pyelonephritis (APN). Promoter activity of the single SNPs or multiple allelic changes corresponding to the genotype patterns (GPs) was tested. We then conducted a replication study in an independent cohort of adult patients with a history of childhood APN. Last, in vivo effects of the different GPs were examined after therapeutic intravesical inoculation of 19 patients with Escherichia coli 83972. We identified in total eight TLR4 promoter sequence variants in the Swedish control population, forming 19 haplotypes and 29 genotype patterns, some with effects on promoter activity. Compared to symptomatic patients and healthy controls, ABU patients had fewer genotype patterns, and their promoter sequence variants reduced TLR4 expression in response to infection. The ABU associated GPs also reduced innate immune responses in patients who were subjected to therapeutic urinary E. coli tract inoculation.

Conclusions

The results suggest that genetic variation in the TLR4 promoter may be an essential, largely overlooked mechanism to influence TLR4 expression and UTI susceptibility.

Waging war against uropathogenic Escherichia coli: winning back the urinary tract

Urinary tract infection (UTI) caused by uropathogenic Escherichia coli (UPEC) is a substantial economic and societal burden-a formidable public health issue. Symptomatic UTI causes significant discomfort in infected patients, results in lost productivity, predisposes individuals to more serious infections, and usually necessitates antibiotic therapy. There is no licensed vaccine available for prevention of UTI in humans in the United States, likely due to the challenge of targeting a relatively heterogeneous group of pathogenic strains in a unique physiological niche. Despite significant advances in the understanding of UPEC biology, mechanistic details regarding the host response to UTI and full comprehension of genetic loci that influence susceptibility require additional work. Currently, there is an appreciation for the role of classic innate immune responses-from pattern receptor recognition to recruitment of phagocytic cells-that occur during UPEC-mediated UTI. There is, however, a clear disconnect regarding how factors involved in the innate immune response to UPEC stimulate acquired immunity that facilitates enhanced clearance upon reinfection. Unraveling the molecular details of this process is vital in the development of a successful vaccine for prevention of human UTI. Here, we survey the current understanding of host responses to UPEC-mediated UTI with an eye on molecular and cellular factors whose activity may be harnessed by a vaccine that stimulates lasting and sterilizing immunity.

Antimicrobial mechanisms of the urinary tract

The urinary tract is a key system to maintain the homeostasis of the human body. It is relatively open to the outside environment, the perineum, a region highly colonized by bacteria. Bacteria can even be found in urine of healthy individuals. Still, urinary tract infections are far less frequent than it could be expected under these conditions. The high resistance against such infections has been observed already more than 100 years ago. Since then, many antimicrobial mechanisms of the urinary tract have been elucidated. Some questions, however, remain challenges for patients, scientists and health care professionals. In this review, we try to summarize the achieved knowledge about mechanisms, maintaining the urinary tract free of infection. In addition, we discuss their relevance and possible clinical application.

A genetic basis of susceptibility to acute pyelonephritis

Background

For unknown reasons, urinary tract infections (UTIs) are clustered in certain individuals. Here we propose a novel, genetically determined cause of susceptibility to acute pyelonephritis, which is the most severe form of UTI. The IL-8 receptor, CXCR1, was identified as a candidate gene when mIL-8Rh mutant mice developed acute pyelonephritis (APN) with severe tissue damage.

Methods and Findings

We have obtained CXCR1 sequences from two, highly selected APN prone patient groups, and detected three unique mutations and two known polymorphisms with a genotype frequency of 23% and 25% compared to 7% in controls (p<0.001 and p<0.0001, respectively). When reflux was excluded, 54% of the patients had CXCR1 sequence variants. The UTI prone children expressed less CXCR1 protein than the pediatric controls (p<0.0001) and two sequence variants were shown to impair transcription.

Conclusions

The results identify a genetic innate immune deficiency, with a strong link to APN and renal scarring.

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

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

Minireview: functions of the renal tract epithelium in coordinating the innate immune response to infection

Infection of the urinary tract remains one of the most common infections affecting mankind. Renal epithelial cells, being one of the first cells to come into contact with invading organisms, are in a key position to coordinate host defense. The epithelium not only provides a physical barrier to infection, but can also augment the immune response via the production of a number of inflammatory mediators and antimicrobial proteins. Recent work has demonstrated that cells of the innate immune system, including epithelial cells, express toll-like receptors (TLRs), with the capacity to recognize bacterial components. Although the exact mechanisms remain unclear, engagement of TLRs can lead to epithelial cell activation and the production of inflammatory mediators. These include complement proteins, other bactericidal peptides, and chemotactic cytokines. The resulting inflammatory infiltrate serves to aid bacterial clearance, but can also lead to renal damage. In this review, we describe how renal epithelial cells contribute to the innate immune response to ascending urinary tract infection. We specifically relate previous work to more recent developments in this field. An improved understanding of the mechanisms involved may highlight potential therapeutic avenues to aid bacterial clearance and prevent the renal scarring associated with infection.

The host response to urinary tract infection

The authors use the UTI model to identify basic mechanisms of disease pathogenesis, host response induction, and defense. Their studies hold the promise to provide a molecular and genetic explanation for susceptibility to UTI, and to offer more precise tools for diagnosis and therapy of these infections. There are few infections where the host response is understood in such detail and where pathologic host responses can be linked to distinct disease states. The susceptibility to UTI varies greatly in the population. The studies suggest that distinct molecular defects can cause the clinical entity of acute pyelonephritis with renal scarring, and suggest that the susceptibility to UTI in certain patient groups may have a genetic basis. In addition, the distinct signal transduction pathways explain the development of symptoms, and propose that defects in those signaling mechanisms may occur in patients with ABU. In the future, it may be useful to include these host response parameters in the diagnostic arsenal, to help in early detection of patients susceptible to recurrent UTI and renal scarring. These patients may then be offered therapies that strengthen their defense, and be offered close surveillance for recurrences and other complications.

Host defense mechanisms in urinary tract infections

The host response to urinary tract infections is directed against both bacterial surface antigens, as well as bacterial products. The local response is perhaps the most important, with prevention of binding and tissue invasion as the hallmarks. Once an infection is established, the humoral immune system is most active in curtailing the damage and clearing the infecting organism. The prostate has a specialized complex of defenses that serves to reduce the incidence of infections in males.

Pathogenesis of urinary tract infection. Role of host defenses

In the last decade, there have been modest strides made in our understanding of the pathogenesis of urinary tract infections (UTIs). Matching the advances achieved in unraveling the complexities of bacterial virulence factors using molecular-genetic techniques has been a parallel increase in knowledge of host defense mechanisms. Host susceptibility to UTI in the past has been predominantly studied in patients with structural (obstruction) or functional abnormalities (diabetes mellitus); however, most patients with UTIs have no such demonstrable abnormalities, hence attention has now focused on host behavioral factors in addition to genetically determined cellular mechanisms that predispose to sporadic and recurrent UTI.

Ciclosporin-dependent, nu-independent, mucosal interleukin 6 response to gram-negative bacteria

Regulation of the mucosal inflammatory response to Gram-negative bacteria was analysed. The interleukin 6 (IL-6) secretion, influx of polymorphonuclear leucocytes into urine, and bacterial clearance from the kidneys were compared between Balb/c (nu/nu) and nu/+/- mice, with and without ciclosporin (CsA) treatment. There was no significant influence of the nu genotype on any of the host responses measured. CsA pretreatment significantly decreased Il-6 secretion in both nu/nu and nu/+/- mice, but did not affect bacterial clearance or the leucocyte response in any mouse strain tested. Tissue damage, in addition to bacterial infection, resulted in significantly higher levels of IL-6 than bacterial infection alone. Tissue-damaged mice were significantly less likely to clear the bacterial infection than their non-damaged counterparts, but there was no significant difference in the leucocyte response. CsA pretreatment did not significantly reduce the levels of IL-6 in the tissue-damaged mice. These results demonstrate that the mucosal inflammatory response to Gram-negative infection, including IL-6 secretion, is nu-independent, and that bacterial infection alone or in combination with tissue damage induce IL-6 secretion by two different pathways.

Roles of spleen and liver in the clearance of Escherichia coli K1 bacteraemia in infant rats

The age-dependent increase in resistance of infant rats to K1 E. coli infection was studied by analysing the clearance of intravenously injected radiolabelled O18:K1 E. coli bacteria. In susceptible 7-day-old rats, the rate of reticuloendothelial clearance could not compete with bacterial multiplication, while the resistance of 18-day-old rats was attributed to the increased sequestration of bacteria in the spleen. After passive immunization with rat monoclonal anti-O18 IgG2b, the O18:K1 E. coli were rapidly cleared by the liver in both age groups. O1:K1, O18:K5 and O18:K- E. coli, which activate complement in an antibody-independent manner and are apathogenic for 7-day-old rats, were also rapidly sequestered in the liver. 7-day-old rats developed a fulminant bacteraemia after receiving 100 O18:K1 E. coli intravenously. After several hours a transient decrease in the level of bacteraemia was observed. However, the clearance remained incomplete, resulting in persistent bacteraemia and death. Endotoxin-responsive infant mice are able to clear the bacteraemia completely after a similar initial phase of bacterial multiplication while no clearance is observed in endotoxin-hypo-responsive mice. The marked host specificity of K1 E. coli infection thus appears to be related to differences in a clearance mechanism which may be sustained by an endotoxin-induced inflammatory response.

Host factors in the resistance of newborn mice to K1 Escherichia coli infection

It is not clear which factors are responsible for the deficient resistance of human neonates to K1 E. coli sepsis and meningitis. To evaluate the relative importance of different defense mechanisms against bacterial invasion, we have analyzed the sensitivity of newborn mice with known immune deficiencies to infection after oral challenge with virulent K1 E. coli. T and B lymphocyte and complement (C5) defects had no significant effect on natural resistance. In contrast, both endotoxin-hyporesponsive mouse strains tested were highly sensitive. This susceptibility to infection was strongly age dependent. Infant endotoxin-hyporesponsive mice were killed by i.p. injection of less than ten virulent K1 E. coli cells. In contrast, endotoxin-responsive animals and F1 hybrids derived from crosses between endotoxin-responsive and hyporesponsive mice survived an injection with up to 10(4) bacteria. Mutants of a virulent 018:K1 E. coli strain defective in the synthesis of the capsular polysaccharide or the O-antigen of lipopolysaccharide were avirulent as were 01:K1 bacteria, which are under-represented among E. coli isolates from neonatal meningitis. Endotoxin-hyporesponsive mice were protected from lethal bacterial challenge by monoclonal IgG specific for the O-antigen of the challenge strain or by human recombinant interleukin 1. A fulminant bacterial multiplication in the bloodstream of endotoxin-hyporesponsive mice was observed after i.v. injection of 100 virulent K1 E. coli cells. Persistent bacteremia with 10(5) to 10(6) bacteria per ml of blood resulted in death of the animals one to two days after challenge. In the bloodstream of endotoxin-responsive mice the bacteria proliferated to a comparable extent within the first 6 h after challenge. Thereafter they were rapidly cleared from the circulation and the animals recovered from the infection.

Non-antibiotic prevention of urinary tract infection

The identification of several glycoconjugates as receptors for attaching bacteria has resulted in optimism regarding the use of receptor analogues in preventing infection. The structure of receptor-active oligosaccharides and the patient groups which might benefit from such treatment are most thoroughly understood for urinary tract infections. Prevention of adhesion and delay or decrease of infection was achieved using oligosaccharides from the globoseries of glycolipids containing Gal alpha 1----4Gal. This minimal receptor structure as a free saccharide was, however, not sufficient. It was the intact P, P1 and pk determinants which showed optimal activity in vitro. In addition, protection against experimental UTI results from previous exposure to whole bacteria or isolated antigens. The mechanism(s) of protection and their relevance in clinical UTI remain to be defined.

Difference in susceptibility to gram-negative urinary tract infection between C3H/HeJ and C3H/HeN mice

The difference in susceptibility to urinary tract infection between C3H/HeJ and C3H/HeN mice was tested for with gram-negative strains differing in lipopolysaccharide composition. Recently, impaired clearance of Escherichia coli from the kidney of C3H/HeJ compared to C3H/HeN mice was shown to be correlated with the LPS low responsiveness. In this study, a difference in clearance from the kidneys of C3H/HeJ and C3H/HeN mice was found only with lipopolysaccharide-containing bacteria. Gram-positive bacteria, e.g., Staphylococcus saprophyticus and Streptococcus agalactiae, were recovered in essentially equal numbers from the kidneys of mice of both strains. In contrast, of the lipopolysaccharide-containing strains used, all persisted in higher numbers in the kidneys of C3H/HeJ mice than in the kidneys of C3H/HeN mice. Variations in the O side chain did not eliminate this difference. E. coli Hu734 O75+K5+ and the rfb- mutant O75-K5+ remained in similar numbers in C3H/HeJ mice, although O75-K5+ was eliminated more rapidly in C3H/HeN mice. The core structure did not affect the differential persistence in the two mouse strains. The rfb mutants with R1-R4 cores were eliminated after 24 h from the C3H/HeN mice, but remained in significant numbers in the kidneys of C3H/HeJ mice. Even the Re mutant of Salmonella minnesota persisted in low numbers in C3H/HeJ mice. The relative bacterial recovery from either mouse strain was related to the overall virulence of the infecting bacterial strain, but the difference between C3H/HeJ and C3H/HeN mice was associated with responsiveness to parts of lipopolysaccharide common to the bacterial strains tested.

Non-antibiotic prevention of urinary tract infection

The identification of several glycoconjugates as receptors for attaching bacteria has resulted in optimism regarding the use of receptor analogues in preventing infection. The structure of receptor-active oligosaccharides and the patient groups which might benefit from such treatment are most thoroughly understood for urinary tract infections. Prevention of adhesion and delay or decrease of infection was achieved using oligosaccharides from the globoseries of glycolipids containing Gal alpha 1----4Gal. This minimal receptor structure as a free saccharide was, however, not sufficient. It was the intact P, P1 and pk determinants which showed optimal activity in vitro. In addition, protection against experimental UTI results from previous exposure to whole bacteria or isolated antigens. The mechanism(s) of protection and their relevance in clinical UTI remain to be defined.