Pathogenesis Of Urinary Tract Infections Research Articles

Identification and characterization of a novel uropathogenic Escherichia coli-associated fimbrial gene cluster.

Recently, we identified a fimbrial usher gene in uropathogenic Escherichia coli strain CFT073 that is absent from an E. coli laboratory strain. Analysis of the CFT073 genome indicates that this fimbrial usher gene is part of a novel fimbrial gene cluster, aufABCDEFG. Analysis of a collection of pathogenic and commensal strains of E. coli and related species revealed that the auf gene cluster was significantly associated with uropathogenic E. coli isolates. For in vitro expression analysis of the auf gene cluster, RNA was isolated from CFT073 bacteria grown to the exponential or stationary phase in Luria-Bertani broth and reverse transcriptase PCR (RT-PCR) with oligonucleotide primers specific to the major subunit, aufA, was performed. We found that aufA is expressed in CFT073 only during the exponential growth phase; however, no expression of AufA protein was observed by Western blotting, indicating that under these conditions, the expression of the auf gene cluster is low. To determine if the auf gene cluster is expressed in vivo, RT-PCR was performed on bacteria from urine samples of mice infected with CFT073. Out of three independent experiments, we were able to detect expression of aufA at least once at 4, 24, and 48 h of infection, indicating that the auf gene cluster is expressed in the murine urinary tract. Furthermore, antisera from mice infected with CFT073 reacted with recombinant AufA in an enzyme-linked immunosorbent assay. To identify the structure encoded by the auf gene cluster, a recombinant plasmid containing the auf gene cluster under the T7 promoter was introduced into the E. coli BL-21 (AI) strain. Immunogold labeling using AufA antiserum revealed the presence of amorphous material extending from the surface of BL-21 cells. No hemagglutination or cellular adherence properties were detected in association with expression of AufA. Deletion of the entire auf gene cluster had no effect on the ability of CFT073 to colonize the kidney, bladder, or urine of mice. In addition, no significant histological differences between the parent and aufC mutant strain were observed. Therefore, Auf is a uropathogenic E. coli-associated structure that plays an uncertain role in the pathogenesis of urinary tract infections.

Identification of a gene encoding heat-resistant agglutinin in Escherichia coli as a putative virulence factor in urinary tract infection.

Escherichia coli causes the vast majority of urinary tract infections (UTI) in both ambulatory and hospital patients. Several uropathogenic virulence factors have been identified, but half of all E. coli isolates that cause UTI have none or only one of the known virulence factors. Thus, it is reasonable to presume that other bacterial factors may be important in UTI pathogenesis. In order to find additional uropathogenic E. coli genes, we used genomic subtraction to identify DNA regions present in a uropathogenic strain of E. coli (1128-11). Genomic subtraction yielded 40 tester-specific fragments, including a novel heat-resistant agglutinin (hra) gene fragment. hra occurred in 55% of 486 UTI strains compared to 28% of 165 rectal strains (P = 0.001). The hra gene in 1128-11 was cloned, sequenced, and found to have 91% homology to the hra gene from E. coli meningitis strain RS218. The genetic organization of genes flanking hra in 1128-11 is distinct from the hra found in E. coli strains J96 and RS218. In our UTI and rectal specimen collections, hra was positively associated with a number of known virulence genes, including pathogenicity island genes hly and cnf, which are absent in 1128-11. The presence of hra in 1128-11 independent of hly/cnf suggests multiple mechanisms by which hra can be acquired by pathogenic E. coli strains. The flanking genes suggest that in 1128-11, hra may be part of a novel variant of a pathogenicity island V.

Pathogenesis of urinary tract infections: a review.

Pathogenesis of urinary tract infections (UTIs) is not well-understood. In this paper, we review the current understanding of UTIs, particularly in relationship to individuals using intermittent catheterization. Relationships exist between the human host, infectious agent and the environment. In the human host, the urethra connects the bladder to potential infectious agents on the perineum. A high-pressure zone exists within the urethra at a point where the urethra passes through the urogenital diaphragm. This zone creates a natural barrier to ascent of organisms colonized in the distal urethra and the bladder itself has natural defences against invading organisms. The interaction of host defences with bacteria (infectious agent) determines whether or not the bacteria persist. A small number of bacteria and some types of bacteria are controlled more effectively by natural bladder defence mechanisms and frequent bladder emptying than a large number of bacteria. Escherichia coli, coliforms and enterococci are considered common bacterial causes of UTIs and are found in high numbers on the perineum. Intermittent catheterization is an effective way of bladder emptying but as an invasive procedure it remains a risk factor in the development of UTI.

Type 1 fimbriae and extracellular polysaccharides are preeminent uropathogenic Escherichia coli virulence determinants in the murine urinary tract.

Escherichia coli is the leading cause of urinary tract infections (UTIs). Despite the association of numerous bacterial factors with uropathogenic E. coli (UPEC), few such factors have been proved to be required for UTI in animal models. Previous investigations of urovirulence factors have relied on prior identification of phenotypic characteristics. We used signature-tagged mutagenesis (STM) in an unbiased effort to identify genes that are essential for UPEC survival within the murine urinary tract. A library of 2049 transposon mutants of the prototypic UPEC strain CFT073 was constructed using mini-Tn5km2 carrying 92 unique tags and screened in a murine model of ascending UTI. After initial screening followed by confirmation in co-infection experiments, 19 survival-defective mutants were identified. These mutants were recovered in numbers 101- to 106-fold less than the wild type in the bladder, kidneys or urine or at more than one site. The transposon junctions from each attenuated mutant were sequenced and analysed. Mutations were found in: (i) the type 1 fimbrial operon; (ii) genes involved in the biosyn-thesis of extracellular polysaccharides including group I capsule, group II capsule and enterobacterial common antigen; (iii) genes involved in metabolic pathways; and (iv) genes with unknown function. Five of the genes identified are absent from the genome of the E. coli K-12 strain. Mutations in type 1 fimbrial genes resulted in severely attenuated colonization, even in the case of a mutant with an insertion upstream of the fim operon that affected the rate of fimbrial switching from the 'off' to the 'on' phase. Three mutants had insertions in a new type II capsule biosynthesis locus on a pathogenicity island and were impaired in the production of capsule in vivo. An additional mutant with an insertion in wecE was unable to synthesize enterobacterial common antigen. These results confirm the pre-eminence of type 1 fimbriae, establish the importance of extracellular polysaccharides in the pathogenesis of UTI and identify new urovirulence determinants.

Sat, the secreted autotransporter toxin of uropathogenic Escherichia coli, is a vacuolating cytotoxin for bladder and kidney epithelial cells.

The secreted autotransporter toxin (Sat) of uropathogenic Escherichia coli exhibits cytopathic activity upon incubation with HEp-2 cells. We further investigated the effects of Sat on cell lines more relevant to the urinary tract, namely, those derived from bladder and kidney epithelium. Sat elicited elongation of cells and apparent loosening of cellular junctions upon incubation with Vero kidney cells. Additionally, incubation with Sat triggered significant vacuolation within the cytoplasm of both human bladder (CRL-1749) and kidney (CRL-1573) cell lines. This activity has been associated with only a few other known toxins. Following transurethral infection of CBA mice with a sat mutant, no reduction of CFU in urine, bladder, or kidney tissue was seen compared to that in mice infected with wild-type E. coli CFT073. However, significant histological changes were observed within the kidneys of mice infected with wild-type E. coli CFT073, including dissolution of the glomerular membrane and vacuolation of proximal tubule cells. Such damage was not observed in kidney sections of mice infected with a Sat-deficient mutant. These results indicate that Sat, a vacuolating cytotoxin expressed by uropathogenic E. coli CFT073, elicits defined damage to kidney epithelium during upper urinary tract infection and thus contributes to pathogenesis of urinary tract infection.

Urinary tract infections: pathogenesis and related conditions.

This paper deals with main aspects of pathogenesis of urinary tract infection (UTI). Bacterial and host-related factors such as defense mechanisms and predisposing factors are described. Special aspects of UTI in elderly patients and during pregnancy are discussed. Recurrent cystitis and prophylactic measures are also reported.

Pathogenesis of bacteriuria in women with diabetes mellitus

Women with diabetes mellitus (DM) have asymptomatic bacteriuria (ASB) and symptomatic urinary tract infections (UTIs) more often than women without DM. The increased prevalence of bacteriuria in diabetic patients can be the result of differences in the host responses between diabetic and nondiabetic patients, or a difference in the infecting bacterium itself. We have shown that the increased prevalence of ASB in diabetic women is not the result of a difference in bacteria, because the same number of virulence factors was found in the infecting Escherichia coli (most common causative microorganism of ASB) in our diabetic women with ASB, as listed in the literature for nondiabetic patients with ASB. We found that bacterial growth in vitro was increased after the addition of different glucose concentrations, as found in urine of poorly controlled patients. However, we could not confirm that glucosuria was a risk factor for ASB in vivo. In addition, we demonstrated that women with both DM and ASB have lower urinary cytokine and leukocyte concentrations than women without DM but with ASB. Finally, we found that E. coli expressing type 1 fimbriae (the virulence factor that plays an important role in the pathogenesis of UTIs) adhere better to uroepithelial cells of women with DM compared with the cells of women without DM.

Distribution and susceptibility of Candida species isolated in the Medical University of Debrecen.

Data of Candida albicans and non-albicans Candida species isolated during the 1997-2000 period in the Medical and Health Science Center of the University of Debrecen are analysed. The number of yeast isolates increased from 408 to 1213 per year during this period. Dominance of C. albicans has been persistent, but a slight increase of C. glabrata and C. krusei could be observed. Distribution of different Candida species isolated from 16 body sites indicates that C. albicans seems to be still the most aggressive Candida species. Investigation of 244 urinary Candida isolates (parallel with bacterial cultures) suggests that tha aetiological role of Candida species in the pathogenesis of urinary tract infections can be hypothesized if colony forming unit (CFU) number of yeasts is higher than 10(4)/ml and bacteria are present in low CFU number or are absent. Antifungal susceptibility testing of C. albicans, C. glabrata, C. tropicalis and C. krusei against Flucytosine, Amphotericin-B, Miconazole, Ketoconazole and Fluconazole suggests that Amphotericin-B is still the most effective antifungal agent. Finally, the problems in judging the aetiological role of isolated Candida species in the pathogenesis of different types of diseases are critically discussed.

Bacterial adherence and immune response in recurrent urinary tract infection

Objective: To study the significance of bacterial adherence and humoral immune response in the pathogenesis of recurrent urinary tract infection in adult women. Methods: The study population consisted of 30 women with recurrent urinary tract infection (UTI) and 30 healthy women as controls. Bacterial adherence to vaginal epithelial cells was studied. The concentration of serum and urine antibodies against mixed coliform antigen and clinical isolate was determined by enzyme-linked immunosorbant assay (ELISA). The surface hydrophobicity of the organisms was determined. Student's unpaired t-test and Pearson's correlation coefficient test were used in the statistical analysis. Results: There was an increased adherence of bacteria to vaginal epithelial cells of women with recurrent UTI. The SIgA level in urine was low compared with other antibodies. There was good correlation between the level of free urinary IgG antibody and bacterial adherence. Conclusions: This study showed that increased receptivity of vaginal epithelial cells to pathogens and lower local immunity may play an important role in the pathogenesis of recurrent UTI in females.

THE PRESENCE OF THE VIRULENCE ISLAND CONTAINING THE USP GENE IN UROPATHOGENIC ESCHERICHIA COLI IS ASSOCIATED WITH URINARY TRACT INFECTION IN AN EXPERIMENTAL MOUSE MODEL

A putative virulence island commonly noted in the genome of uropathogenic Escherichia coli strains has recently been reported. We have observed that the island includes a gene consisting of a protein designated uropathogenic specific protein (usp) and 3 small open reading frames (orfU1-3). In our current study we assessed the importance of the genes located in the putative virulence island in the pathogenesis of urinary tract infection using a mouse pyelonephritis model. A total of 427 E. coli strains isolated from the urine of 194, 76 and 107 subjects suffering from cystitis, pyelonephritis and prostatitis, respectively, and 50 isolates from the feces of healthy individuals were examined for genotypes and serotypes. In addition, several recombinant E. coli strains possessing usp and/or orfU1 to 3 were constructed for evaluating the significance of these genes using an experimental pyelonephritis mouse model. The usp was significantly more often associated with uropathogenic E. coli strains (79.4% from cystitis, 93.4% from pyelonephritis and 88.8% from prostatitis) than with fecal E. coli strains from healthy individuals (24%). Furthermore, usp was frequently associated with all common serotypes of uropathogenic E. coli (71.7% to 100%). In challenge experiments using the mouse urinary tract infection model the vector possessing usp significantly enhanced the infectibility of the E. coli host cell, whereas the 3 small proteins at the downstream of usp failed to show the effect. Our results indicate that usp may contribute to the causation of urinary tract infection and may be considered a major virulence determinant of uropathogenic E. coli.

Recurrent urinary tract infection in women

Recurrent urinary tract infections (UTI) are common among young healthy women even though they generally have anatomically and physiologically normal urinary tracts. Women with recurrent UTI have an increased susceptibility to vaginal colonization with uropathogens, which is due to a greater propensity for uropathogenic coliforms to adhere to uroepithelial cells. Risk factors for recurrent UTI include sexual intercourse, use of spermicidal products, having a first UTI at an early age, and having a maternal history of UTIs. Inherited factors may be important in some women with recurrent UTI. Many factors thought to predispose to recurrent UTI in women, such as pre- and post-coital voiding patterns, frequency of urination, wiping patterns, and douching have not been proven to be risk factors for UTI. In contrast to the predominantly behavioral risk factors for young women, mechanical and/or physiological factors that affect bladder emptying are most strongly associated with recurrent UTI in healthy postmenopausal women. The management of recurrent UTI is the same as that for sporadic UTI except that the likelihood of infection with an antibiotic resistant uropathogen is higher in women who have received recent antimicrobials. Strategies to prevent recurrent UTI in young women should include education about the association of recurrent UTI with frequency of sexual intercourse and the usage of spermicide-containing products. Continuous or post-coital prophylaxis with low-dose antimicrobials or intermittent self-treatment with antimicrobials have all been demonstrated to be effective in managing recurrent uncomplicated UTIs in women. Estrogen use is very effective in preventing recurrent UTI in post-menopausal women. Exciting new approaches to prevent recurrent UTI include the use of probiotics and vaccines. Further understanding of the pathogenesis of UTI will lead to more effective and safer methods to prevent these frequent infections.

Urinary tract infections: disease panorama and challenges.

The major goal of this conference was to review new advances in our undertaking of the pathogenesis of urinary tract infections (UTIs) from the perspective of both the pathogen and the host. This initial presentation provided an appropriate context for subsequent discussion by providing an overview of the etiology and epidemiology of UTI, diagnostic and therapeutic approaches, current management strategies, evolution of antimicrobial resistance, and current approaches to prevention.

Tamm-Horsfall Protein Binds to Type 1 Fimbriated Escherichia coli and Prevents E. coli from Binding to Uroplakin Ia and Ib Receptors

The adherence of uropathogenic Escherichia coli to the urothelial surface, a critical first step in the pathogenesis of urinary tract infection (UTI), is controlled by three key elements: E. coli adhesins, host receptors, and host defense mechanisms. Although much has been learned about E. coli adhesins and their urothelial receptors, little is known about the role of host defense in the adherence process. Here we show that Tamm-Horsfall protein (THP) is the principal urinary protein that binds specifically to type 1 fimbriated E. coli, the main cause of UTI. The binding was highly specific and saturable and could be inhibited by d-mannose and abolished by endoglycosidase H treatment of THP, suggesting that the binding is mediated by the high-mannose moieties of THP. It is species-conserved, occurring in both human and mouse THPs. In addition, the binding to THP was much greater with an E. coli strain bearing a phenotypic variant of the type 1 fimbrial FimH adhesin characteristic of those prevalent in UTI isolates compared with the one prevalent in isolates from the large intestine of healthy individuals. Finally, a physiological concentration of THP completely abolished the binding of type 1 fimbriated E. coli to uroplakins Ia and Ib, two putative urothelial receptors for type 1 fimbriae. These results establish, on a functional level, that THP contains conserved high-mannose moieties capable of specific interaction with type 1 fimbriae and strongly suggest that this major urinary glycoprotein is a key urinary anti-adherence factor serving to prevent type 1 fimbriated E. coli from binding to the urothelial receptors.

Identification of Putative Urovirulence Genes by Subtractive Cloning

The urinary tract is among the most common sites of both community-acquired and nosocomial infections, and Escherichia coli is the most common etiologic agent of these infections. Infections by uropathogenic E. coli (UPEC) can range from asymptomatic bacteriuria to cystitis and acute pyelonephritis to bacteremia and sepsis [1]. There is ample evidence that UPEC differs from most E. coli strains isolated from the feces of healthy individuals. Numerous epidemiologic studies have suggested a role for P and other fimbriae, afimbrial adhesins, hemolysin, aerobactin, capsule, and cytotoxic necrotizing factor in the pathogenesis of urinary tract infections (UTIs) [2]. However, many of these factors have not been proven to be involved in disease. UPEC and other pathogenic E. coli harbor pathogenicity islands (PAIs) and possess genomes that are 20% larger than E. coli K-12 and other nonpathogenic fecal strains [3], suggesting the presence of many pathogenesis genes that have yet to be discovered. In the present study, we employed a genomic approach to discover genes that are present in a very potent UPEC strain but absent from an E. coli laboratory strain.

The role of P fimbriae for colonization and host response induction in the human urinary tract.

Bacterial attachment is thought to enhance virulence by promoting colonization of the urinary tract and by attacking tissue [1]. Uropathogenic Escherichia coli express several classes of fimbriae-associated adhesins that mediate attachment through specific binding to different glycoconjugate receptors [2] (for review see Mirelman [3]). P fimbriae, encoded by the pap gene cluster, show the most clear-cut association with virulence as defined by acute disease severity [4]. It has been proposed that P fimbriae augment the virulence of uropathogenic E. coli at different stages during the pathogenesis of urinary tract infection (UTI). pap+ strains remain longer in the intestinal flora and spread more efficiently to the urinary tract than do papstrains [5]. Once in the urinary tract, P-fimbriated strains establish bacteriuria and may cross the epithelial barrier into the bloodstream [6]. P fimbriae enhance epithelial cytokine responses in vitro [7] and in the mouse UTI model [8]. The role of P fimbriae per se for colonization and host response induction is not clear and has been the subject of some discussion. While fimbriae-mediated attachment enhances bac-

Phytochemical and Antimicrobial Studies of Bridelia crenulata

Bridelia crenulata Roxb., Euphorbiaceae, is known as Adamaruthu, Maarivengai, Mulvengai and Oothiravengai in the Tamil language. The women of the Paliyan tribes in Tirunelveli district of Tamil Nadu in India consume a bark extract to cure menorrhagia. Isolation yielded friedelin, epi -friedelinol, n -octacosanol, a-amyrin, ß-sitosterol, ß-sitosterol-3-ß-D-glucopyranoside and luteoforol. Aqueous and methanolic extracts and their fractions were tested against 10 human pathogenic bacteria and 4 fungal strains. Inhibitory activities were maximum in the chloroform – methanol (1 : 1) fraction of the methanolic extract against E. coli, K. pneumoniae and P. aeruginosa, which are responsible for the pathogenesis of urinary tract infection. The study provides scientific evidence for the efficacy of the use.

Urinary Tract Infections: Current approaches, future directions

Urinary tract infection (UTI) is a common problem that is distressing for patients and costly for the healthcare system. UTIs commonly affect young, sexually active women; the elderly; and patients who have predisposing factors, such as catheterization. Recurrent infections are likely to occur in all these patients groups. Patients who are pregnant or have predisposing factors are at increased risk for complications related to untreated UTIs, such as long-term renal damage. Given these risks and the public health burden associated with the condition, it is important that clinicians have up-to-date information regarding the classification, symptoms, pathogenesis, and empiric treatment of UTIs.

Pathogenesis of Urinary Tract Infection: the Role of Sexual Behavior and Sexual Transmission.

Acute urinary tract infection (UTI) is an extremely common clinical entity that affects almost half of all women in the United States, and accounts for more than 7 million physician visits, annually, in this country. Sexual behavior and UTI history are the most important predictors of UTI risk among sexually active young women. Whether sexual behavior has similar impact on UTI risk in older women is unknown. Postcoital prophylaxis has been investigated as a strategy for the prevention of recurrent UTI in sexually active women. There are conflicting data regarding the role of voiding habits in relation to sexual intercourse and the risk of UTI. Finally, there are interesting epidemiologic studies suggesting that uropathogenic Escherichia coli may be transmitted between sex partners. We review the recent literature regarding these different areas, and comment on the potential role of sexual transmission in UTI.

Pathogenesis of urinary tract infections: an update

The pathogenesis of uncomplicated urinary tract infection (UTI) is complex and influenced by many host biological and behavioural factors and by properties of the infecting uropathogens. Most uncomplicated UTIs in women are not associated with underlying functional or anatomical abnormalities of the urinary tract, whereas sexual intercourse, spermicide use, a history of recurrent UTI and recent antimicrobial chemotherapy are important risk factors. A maternal history of UTI and young age at first UTI, as well as sexual intercourse and spermicide use, are risk factors for recurrent UTI in young women. In some young healthy women, especially those with 'low UTI risk' behaviour, features of pelvic anatomy appear to be associated with UTI risk. In postmenopausal women, anatomical and functional characteristics of the genitourinary tract are more strongly associated with UTI risk than in younger women. A genetic predisposition to recurrent UTI is suggested by the association of recurrent UTI in certain age groups with the ABH blood group non-secretor phenotype, a maternal history of UTI and early age at onset of UTI. Virulence determinants of uropathogens are much more important in the normal host than in the host who has a functional or anatomical abnormality of the genitourinary tract.

Internalization of extraintestinal Escherichia coli 018 strains by epithelial cells is modulated by EGF, insulin, and effectors of transmembrane signal transduction

Adhesion to and internalization into host cells is an essential step in the pathogenesis of various bacterial infections. Here we investigated the effects of growth factors on the internalization of Escherichia coli O18 strains isolated from patients with urinary tract infection (UTI) by human epithelial cells. A dramatic increase in the uptake of Escherichia coli was observed after treatment of epithelial cells with epidermal growth factor (EGF) and to a lower extent with insulin. EGF-dependent internalization can be suppressed by tyrosine kinase inhibitors suggesting an involvement of the receptor tyrosine kinases in the regulation of the endocytotic process. Inhibitors of phospholipase A 2, lipoxygenase, and cyclooxygenase significantly decreased internalization of bacteria induced by EGF. Finally, the specific inhibitor of PI 3-kinases Wortmannin was shown to suppress completely the EGF-indepemdent internalization. The data of this analysis indicate the involvement of several signaling paths in bacterial internalization of uropathogenic Escherichia coli O18 strains and contribute to the comprehension of the pathogenesis of recurrent UTI.