P-fimbriated Escherichia coli in children with acute cystitis

Fifteen-minute consultation: Why and how do children get urinary tract infections?

This paper describes urinary tract infections (UTI) from the perspective of a disturbed balance between bacterial virulence and host defence. In some children, a UTI is caused by a virulent Escherichia coli, while in other cases children with abnormal renal tracts can get infected by almost any bacteria. Such knowledge can help in guiding treatment, investigations and follow-up of a child with a UTI.

P-fimbriated Escherichia coli in adults with renal scarring and pyelonephritis

The commonest organism in urinary tract infections (UTI) is Escherichia coli. Pyelonephritogenic E.coli strains possess P-fimbriae which firmly attach to uroepithelial cells by recognition of a carbohydrate structure, alpha-D-Galp-(1-4)-beta-D-Galp, which is confined within all glycosphingolipids related to the human P-blood group antigens. Several investigators have studied virulence properties of E.coli and host resistance in relation to UTI. Uroepithelial cells from children and women with recurrent UTI have an increased capacity to bind E.coli. In contrast to previous studies the present one deals with patients with renal scarring, who constitute the major risk group among patients with UTI. P-fimbriae mediated binding to uroepithelial cells was studied and the risk of recurrent UTI in patients with renal scarring was determined. Ninety per cent of the E.coli isolates from female patients with acute non-obstructive pyelonephritis in this study possess P-fimbriae (I). The fecal E.coli colonies obtained from these patients were P-fimbriated in 55% compared to 11% of the fecal E.coli colonies from healthy controls. The P-blood group distribution in 56 female patients with renal scarring and a history of febrile UTI was the same as in a control group of 39 healthy subjects (II). A history of recurrent and/or early infections did not increase the percentage of the P1 blood group phenotype. Forty-nine female patients with renal scarring were prospectively investigated for the incidence of symptomatic UTI in relation to fecal colonization with P-fimbriated E.coli (III). Fifty-three per cent of the patients had altogether 65 episodes of symptomatic UTI during the three-year follow-up (0.036 infections per month). Eight patients (16%) had nine attacks of acute pyelonephritis and 4/5 of the tested E.coli strains from these patients were P-fimbriated. No relationship was demonstrated between the presence of P-fimbriated E.coli in the fecal flora and the development of subsequent acute pyelonephritis. The binding of P-fimbriated E.coli to uroepithelial cells from 19 female patients with renal scarring was studied with the fluorescence-activated cell sorting (FACS) analysis (IV). The uroepithelial cells from the patients with renal scarring exhibited a significantly higher binding capacity (p less than 0.01) than uroepithelial cells from healthy controls. Furthermore, uroepithelial cells from the patients with renal scarring and kidney insufficiency had a higher availability of P-fimbriae receptors on their uroepithelial cells than cells obtained from patients with renal scarring and normal renal function (r = -0.75, p less than 0.001) (V).(ABSTRACT TRUNCATED AT 400 WORDS)

Clonal diversity of Escherichia coli colonizing stools and urinary tracts of young girls

Intestinal carriage of Escherichia coli in prepubertal girls without a history of urinary tract infection was examined by collecting weekly stools and periurethral and urine samples over 3 to 4 weeks of study. Dominant and minor clones were defined by grouping 28 E. coli isolates into clonal types. Multiple enteric clones of E. coli, which changed week to week, were found in the 13 girls during the study (median, 3 clones/girl; range, 1 to 16 clones/girl). Dominance of an enteric clone did not predict persistence in the stool. In only 10 (34%) of the 29 episodes in which a dominant clone present in one weekly sample could have been detected the following week did it persist as the dominant clone in the next weekly sample. In 5 (17%) of the 29 episodes, a dominant clone found in one weekly sample was classified as a minor clone the next week. Both dominant and minor clones were observed to colonize the urinary tract. However, when colonization of the periurethra or bladder urine occurred, it was brief and often did not reflect the dominant stool flora from the same week. In fact, in only 40% of episodes was a clone that was detected either on the periurethra or in the urine also recovered from the stool the same week. Our findings suggest that the intestinal flora of healthy girls is multiclonal with frequent fluctuations in composition.

Induction of protective immunity after escherichia coli bladder infection in primates. Dependence of the globoside-specific P-fimbrial tip adhesin and its cognate receptor

Clinical observations suggest that immune mechanisms affect etiology and course of recurrent cystitis. A primate infection model was used to show that primary bladder infection with a uropathogenic P-fimbriated strain (binding to globoside present in the bladder wall) protects against rechallenge with homologous as well as heterologous Escherichia coli strains for up to 5-6 mo. In contrast, mutant derivatives producing P-fimbriae either lacking the tip adhesin protein or carrying an adhesin for which no bladder receptor was present, were unable to induce protection, even though they generated bladder infections of similar duration as the wild type. Therefore, the protective effect mediated by the adhesin seemed to depend upon the presence of its cognate receptor. Since the wild strain also mediated protection against mutants that lacked the adhesin, our data suggest that the globoside-binding PapG adhesin acts as an adjuvant during infection to enhance a specific response against other bacterial antigens. In fact, the globoside-binding strain DS17, but not the mutant DS17-1, unable to bind to membrane-bound globoside, elicited a secretory IgA response to LPS in urine. These in vivo findings suggest that bacterial adhesin-ligand interactions may have signaling functions of importance for the immune response.

The PapG-adhesin at the tip of P-fimbriae provides Escherichia coli with a competitive edge in experimental bladder infections of cynomolgus monkeys

Human urinary tract infection is an infectious disease that depends on a series of host-microbial interactions. The bacteria first colonize the colon and then the periurethral/vaginal areas; they ascend to and infect first the bladder and then the kidneys. Expression of Escherichia coli P-fimbriae constitutes the strongest correlation to renal pathogenicity, but is also related to first-time cystitis in children. The role of P-fimbriae in the preceding steps in the infectious process is unknown. To examine this, we constructed, from a P-fimbriated E. coli strain with a class II G-adhesin preferentially binding to globoside, one isogenic mutant lacking the G-adhesin and another isogenic mutant in which we replaced the papG class II allele with a class III adhesin preferentially binding to the Forssman antigen. We report here the comparison of the adhesin knockout mutant (DS17-8) and the class-switch mutant (DS17-1) with the wild-type (DS17) for in vivo colonization of the gut, vagina, and bladder of cynomolgus monkeys. It was recently shown that the class II tip G-adhesin is a prerequisite for acute pyelonephritis to occur in the monkey model in the absence of other kidney-specific adhesins or obstruction of the urinary flow. Here we show that it is not required for bladder infection but gives a competitive advantage in mixed infections. In the vagina and colon, the G-adhesin gives no competitive advantage.

The Gal(alpha 1-4)Gal-specific tip adhesin of Escherichia coli P-fimbriae is needed for pyelonephritis to occur in the normal urinary tract

Nonobstructive acute pyelonephritis in humans is most often caused by P-fimbriated Escherichia coli. P-fimbriae are heteropolymeric fibers carrying a Gal(alpha 1-4)Gal-specific PapG adhesin at its distal end. The pyelonephritic strain DS17 expresses P-fimbriae from a single gene cluster. A mutant strain, DS17-8, which expresses P-fimbriae tacking the PapG adhesin, was constructed by allelic replacement introducing a 1-bp deletion early in the papG gene. In cynomolgus monkeys, DS17 and DS17-8 were equally able to cause bladder infection, whereas only the wild-type strain DS17 could cause pyelonephritis as monitored by bacteriological, functional, and histopathological criteria. Since DS17, but not DS17-8, adheres to renal tissue, these data underscore the critical role of microbial adherence to host tissues in infectious disease and strongly suggest that the PapG tip adhesin of P-fimbriae is essential in the pathogenesis of human kidney infection.

Binding of uropathogenic Escherichia coli R45 to glycolipids extracted from vaginal epithelial cells is dependent on histo-blood group secretor status

Women with a history of recurrent Escherichia coli urinary tract infections (UTIs) are two to three times more likely to be nonsecretors of histo-blood group antigens than are women without such a history. Further, uroepithelial cells from women who are nonsecretors show enhanced adherence of uropathogenic E. coli compared with cells from secretors. To investigate the hypothesis that nonsecretors express unique receptors for uropathogenic E. coli related to their genetic background, we extracted glycosphingolipids (GSLs) from vaginal epithelial cells collected from nonsecretors and secretors and used an assay in which radiolabeled uropathogenic E. coli were bound to these GSLs separated on TLC plates. An E. coli strain (R45) expressing both P and F adhesins, which was isolated from one of these patients' UTIs, was metabolically labeled with 35S for the TLC binding assay. The radiolabeled E. coli R45 bound to two extended globo-series GSLs, sialosyl gal-globoside (SGG) and disialosyl gal-globoside (DSGG), found in the GSL extracts from nonsecretors but not from secretors. The identity of SGG in the nonsecretor GSL extracts was confirmed in radioimmunoassays using an mAb to SGG and in immunofluorescence assays with this mAb and native vaginal epithelial cells. We show that SGG and DSGG are selectively expressed by epithelial cells of nonsecretors, presumably as a result of sialylation of the gal-globoside precursor glycolipid, which in secretors is fucosylated and processed to ABH antigens. The presence of SGG and DSGG may account for the increased binding of E. coli to uroepithelial cells from nonsecretors and for their increased susceptibility to recurrent UTI.

Single dose treatment of cystitis in children

The efficacy of single dose treatment with trimethoprim compared to a 5-day course with the same drug was investigated in 100 children, 3-12 years, with isolated episodes of symptomatic non-febrile urinary tract infection. Cure, defined as sterile urine during the first week after treatment, was achieved in 74% (37/50) in the single dose group compared to 86% (43/50) in the 5-day treatment group. The difference was not statistically significant (chi 2 = 2.25, p = 0.134 two-tailed). The cure rates in relation to P-fimbriation of the infecting E. coli strains were similar in the two groups. During the 6 month follow-up, six children in each treatment group had one or more reinfections. Extended studies are needed to conclude if single dose and conventional treatment courses are equally effective.

Virulence factors in Escherichia coli urinary tract infection

Uropathogenic strains of Escherichia coli are characterized by the expression of distinctive bacterial properties, products, or structures referred to as virulence factors because they help the organism overcome host defenses and colonize or invade the urinary tract. Virulence factors of recognized importance in the pathogenesis of urinary tract infection (UTI) include adhesins (P fimbriae, certain other mannose-resistant adhesins, and type 1 fimbriae), the aerobactin system, hemolysin, K capsule, and resistance to serum killing. This review summarizes the virtual explosion of information regarding the epidemiology, biochemistry, mechanisms of action, and genetic basis of these urovirulence factors that has occurred in the past decade and identifies areas in need of further study. Virulence factor expression is more common among certain genetically related groups of E. coli which constitute virulent clones within the larger E. coli population. In general, the more virulence factors a strain expresses, the more severe an infection it is able to cause. Certain virulence factors specifically favor the development of pyelonephritis, others favor cystitis, and others favor asymptomatic bacteriuria. The currently defined virulence factors clearly contribute to the virulence of wild-type strains but are usually insufficient in themselves to transform an avirulent organism into a pathogen, demonstrating that other as-yet-undefined virulence properties await discovery. Virulence factor testing is a useful epidemiological and research tool but as yet has no defined clinical role. Immunological and biochemical anti-virulence factor interventions are effective in animal models of UTI and hold promise for the prevention of UTI in humans.

Residual urine in children with acute cystitis and in healthy children: assessment by sonography

Residual urine was assessed by ultrasound in children with single attacks of symptomatic lower urinary tract infection and in healthy controls. Residual urine was found significantly more often in the 39 patients during acute illness as well as during a follow-up of 6 months, compared to 55 control children. Infections caused by P-fimbriated Escherichia coli were not more often associated with residual urine than infections with nonP-fimbriated Escherichia coli or other bacterial species. It is suggested that residual urine is a facilitating host factor among others in the pathogenesis of symptomatic urinary tract infection in childhood.

Incidence of aerobactin-positive Escherichia coli strains in patients with symptomatic urinary tract infection

A total of 323 Escherichia coli strains from children with primary acute non-obstructive pyelonephritis (n = 144) or cystitis (n = 56) and from adults with acute non-obstructive pyelonephritis (n = 66) or cystitis (n = 57) were examined for presence of the aerobactin-mediated iron uptake system and expression of P-fimbriae. Overall, pyelonephritogenic Escherichia coli strains were significantly more often aerobactin-positive (72%) than cystitis strains (42%) (p less than 0.001). Seventy-three percent of the isolates from children with acute pyelonephritis were aerobactin-positive compared to 54% of the cystitis strains (p less than 0.05). Pyelonephritogenic Escherichia coli strains from adults were also significantly more often aerobactin-positive (70%) than cystitis strains (30%) (p less than 0.001). The cystitis strains from children were more often aerobactin-positive than cystitis strains from adult patients (p less than 0.05). There was a significant correlation between presence of the aerobactin-mediated iron uptake system and expression of P-fimbriae in all strains (p less than 0.001).