Characterization of adhesion associated surface properties of uropathogenicEscherichia coli

Escherichia coli was isolated from the urine of patients with pyelonephritis, with urinary tract infections other than pyelonephritis and with asymptomatic bacteriuria. Surface properties of the strains were analyzed by the salting-out aggregation test (SAT), hydrophobic interaction chromatography (HIC), Congo red binding (Crb), agglutination of erythrocytes (MRHA) and latex particles covered by digalactoside (PF) and by adherence to tissue culture cells. In addition, a DNA probe for thepap gene was used. The DNA probe detected the highest proportion of strains withpap gene in the group of patients with pyelonephritis, lower in the urinary tract infections other than pyelonephritis and the lowest in the group with asymptomatic bacteriuria. Tests for P-fimbriae (PF, MRHA) showed a similar distribution. Hydrophobicity measured by SAT and by HIC did not show differences among the tested groups of strains. The results suggest that factors other than the P-fimbriae and hydrophobicity may contribute to the persistence ofE. coli in the urinary tract.     

Pathogenic characteristics of Escherichia coli strains in cases of asymptomatic bacteriuria and symptomatic urinary tract infections

The aim of this study was to examine if E. coli isolated from asymptomatic bacteriuria differed in pathogenic features from strains isolated from symptomatic infections of urinary tract. In this study 130 strains of E. coli isolated from women having asymptomatic bacteriuria and 112 strains isolated from patients with symptoms of urinary tract infection were examined. It was shown that E. coli isolated from patients with symptomatic urinary tract infection showed the more frequently ability to cause mannose-resistant haemagglutination of human erythrocytes, resistance to bactericidal activity of serum and haemolytic properties than those isolated from asymptomatic bacteriuria. These strains showed also the higher ability to adhere to Vero cells in tissue culture. Among E. coli strains isolated from persons with asymptomatic bacteriuria the pathogenic features were most frequently found in strains from healthy women and the most rarely in isolated from diabetic women.     

Untreated asymptomatic bacteriuria in girls: II--Effect of phenoxymethylpenicillin and erythromycin given for intercurrent infections.

OBJECTIVE--To investigate the effects of phenoxymethylpenicillin and erythromycin on urinary isolates from patients with untreated asymptomatic bacteriuria. DESIGN--Retrospective study of subgroup of patients from cohort followed up till the end of 1986. SETTING--Outpatient clinic for children with urinary tract infections. PATIENTS--51 Girls aged under 15 with untreated asymptomatic bacteriuria. INTERVENTIONS--Before 1982 intercurrent infections (mostly tonsillitis or otitis) were treated with phenoxymethylpenicillin; after 1982 erythromycin treatment was preferred. END POINTS--Change of bacterial strain in urinary tract and symptomatic recurrences of disease. MEASUREMENTS AND MAIN RESULTS--Bacteria identified by serotype and electrophoretic type and compared before and after antibiotic treatment. Bacteriuria eradicated and replaced by new strains in most patients treated with phenoxymethylpenicillin, leading to symptomatic recurrences in about 15%. Conversely, patients given erythromycin rarely showed change in bacteriuria and none suffered symptomatic recurrence. CONCLUSIONS--In girls with untreated asymptomatic bacteriuria the use of phenoxymethylpenicillin for intercurrent infections may lead to a change of urinary bacteria and leave them at substantial risk of acute pyelonephritis. With erythromycin this risk is small (2/20 courses in this series).     

Assessment of the Significance of Virulence Factors of Uropathogenic Escherichia coli in Experimental Urinary Tract Infection in Mice

Four Escherichia coli strains, isolated from cystitis patients, belonging to serotype O2:H^? and possessing different combinations of urovirulence factors were examined in an experimental pyelonephritis mouse model to assess the relative importance of virulence factors in causation of urinary tract infections (UTI). The results suggest not only that the each virulence factor has a role in causation of UTI but also that the presence of P fimbriae and production of hemolysin significantly reduced the LD₅₀ and ID₅₀ of the strains in the mouse model. The results also demonstrate that the presence of additional virulence factors acts in an additive or synergetic fashion enhancing the cumulative impact of the strain.     

Virulence of Escherichia coli in acute pyelonephritis,acute cystitis and asymptomatic bacteriuria

E. coli strains were isolated from urine specimens of hospitalised patients with acute pyelonephritis, acute cystitis or asymptomatic bacteriuria (ABU), and tested for virulence in an experimental mouse model. Of 12 pyelonephritisstrains 11 were shown to be virulent and 1 avirulent; of 12 cystitis-strains 4 were virulent and 8 avirulent; of 12 ABU-strains 5 were virulent and 7 avirulent. It is concluded that, while no difference in virulence was found between cystitis-and ABU-strains, pyelonephritis-strains were more often virulent than cystitis-and ABU-strains.No associations could be shown between virulence of the isolated strains and the presence of antibody-coated bacteria in the urine. Common urinary O types were not more often virulent than other O types. No relationship was seen between virulence and the presence of K antigen or the presence of particular K types.     

A Real-Time PCR-Based Semi-Quantitative Breakpoint to Aid in Molecular Identification of Urinary Tract Infections

This study presents a novel approach to aid in diagnosis of urinary tract infections (UTIs). A real-time PCR assay was used to screen for culture-positive urinary specimens and to identify the causative uropathogen. Semi-quantitative breakpoints were used to screen for significant bacteriuria (presence of ≥10⁵ CFU/ml of uropathogens) or low-level bacteriuria (containing between 10³ and 10⁴ CFU/ml of uropathogens). The 16S rDNA-based assay could identify the most prevalent uropathogens using probes for Escherichia coli, Pseudomonas species, Pseudomonas aeruginosa, Staphylococcus species, Staphylococcus aureus, Enterococcus species and Streptococcus species. 330 urinary specimens were analysed and results were compared with conventional urine culture. Using a PCR Ct value of 25 as semi-quantitative breakpoint for significant bacteriuria resulted in a sensitivity and specificity of 97% and 80%, respectively. In 78% of the samples with monomicrobial infections the assay contained probes to detect the bacteria present in the urine specimens and 99% of these uropathogens was correctly identified. Concluding, this proof-of-concept approach demonstrates that the assay can distinguish bacteriuria from no bacteriuria as well as detect the involved uropathogen within 4 hours after sampling, allowing adequate therapy decisions within the same day as well as drastically reduce consequent urine culturing.     

Comparative genomics of Escherichia coli strains causing urinary tract infections

The virulence determinants of uropathogenic Escherichia coli have been studied extensively over the years, but relatively little is known about what differentiates isolates causing various types of urinary tract infections. In this study, we compared the genomic profiles of 45 strains from a range of different clinical backgrounds, i.e., urosepsis, pyelonephritis, cystitis, and asymptomatic bacteriuria (ABU), using comparative genomic hybridization analysis. A microarray based on 31 complete E. coli sequences was used. It emerged that there is little correlation between the genotypes of the strains and their disease categories but strong correlation between the genotype and the phylogenetic group association. Also, very few genetic differences may exist between isolates causing symptomatic and asymptomatic infections. Only relatively few genes that could potentially differentiate between the individual disease categories were identified. Among these were two genomic islands, namely, pathogenicity island (PAI)-CFT073-serU and PAI-CFT073-pheU, which were significantly more associated with the pyelonephritis and urosepsis isolates than with the ABU and cystitis isolates. These two islands harbor genes encoding virulence factors, such as P fimbriae (pyelonephritis-associated fimbriae) and an important immunomodulatory protein, TcpC. It seems that both urovirulence and growth fitness can be attributed to an assortment of genes rather than to a specific gene set. Taken together, urovirulence and fitness are the results of the interplay of a mixture of factors taken from a rich menu of genes.     

Occurrence of genes for P and S fimbriae and hemolysin in urinaryEscherichia coli

Escherichia coli is the common causative agent of urinary tract infections. Sixty-one strains ofE. coli isolated from children with urinary tract infections were tested by colony hybridization for the presence of genes determining P and S fimbriae and hemolysin. Of these strains, 46 possess a gene for hemolysin, 44 for P fimbriae and 28 for S fimbriae. Only 30 strains formed lytic zones around the colonies on plates with sheep erythrocytes. The results indicated that simultaneous occurrence of genes in urinaryE. coli was highest for P fimbriae and hemolysin and lower for other combinations of the tested genes.     

Isolation and characterisation of dog uropathogenic Escherichia coli strains and their fimbriae

A number of Escherichia coli strains have been isolated from dogs with urinary tract infections. These strains have been characterised with respect to their O, K, H, and fimbrial antigens, colicin production, antibiotic resistance, plasmid content and their ability to haemagglutinate erythrocytes from various species. Crossed immunoelectrophoresis of fimbrial extracts, as well as the reaction of partly purified fimbriae of a number of these strains with monoclonal antibodies revealed homology or a strong crossereaction with an F12 fimbrial subunit protein of human uropathogenic E. coli strains. Unlike human F12 fimbriae producing strains, the dog isolates did agglutinate dog erythrocytes in the presence of D-mannose but not human erythrocytes, indicating that the adhesin carried by these strains is different from the adhesin on fimbriae of human uropathogenic E. coli. Similar indications were obtained from experiments with latex beads coated with the receptor for P-fimbriae. These beads were agglutinated by Escherichia coli strains from human urinary tract infections, but not by the dog isolates described here. Preliminary adhesion experiments of human and dog Escherichia coli to human bladder epithelial and canine kidney epithelial cells also showed differences in adhesion depending on the origin of the strain tested.     

Isogenic P-fimbrial deletion mutants of pyelonephritogenic Escherichia coli: the role of α Gal(1–4)β Gal binding in virulence of a wild-type strain

Escherichia coli strains causing acute pyelonephritis often express multiple fimbrial types and haemolysin, which may contribute to their ability to adhere to, and interact with, kidney epithelial cells. Strain CFT073, a pap⁺, sfa⁺, pil⁺, hly⁺ pyelonephritis strain, previously established as virulent in the CBA mouse model of ascending urinary tract infection and cytotoxic for cultured human renal epithelial cells, was selected for construction of isogenic strains. From a gene bank of this strain, two distinct copies of the pap operon were isolated. The two P-fimbrial determinants were sub-cloned into pCVD442, a positive selection suicide vector containing the sacB gene of Bacillus subtilis. Deletion mutations were introduced into each of the two constructs, within papEFG of one operon and papDEFG of the other. Suicide vectors carrying pap deletions were mobilized from E. coli SM10 lambda pir into CFT073 (Nal^R) and cointegrates were passaged on non-selective medium. The first pap mutation was identified by screening a Southern blot of DNA from sucrose-resistant colonies using a papEFG probe. This mutant retained the MRHA⁺ phenotype since a second functional copy of pap was still present. A double pap-deletion mutant, UPEC76, confirmed by Southern blotting, was unable to agglutinate human type O erythrocytes or α Gal(1–4)β Gal-coated latex beads. CBA mice (N =100) were challenged transurethrally with 10⁵, 10⁶, 10⁷, or 10⁹ cfu of strains CFT073 or UPEC76. After one week, quantitative cultures of urine, bladder, and kidney were done and histologic changes were examined. No substantive differences in organism concentration or histological findings between parent and mutant were detected in urine, bladder, or kidney at any challenge concentration. We conclude that adherence by P fimbriae of uro-pathogenic E. coli strain CFT073 plays only a subtle role in the development of acute pyelonephritis in the CBA mouse model.     

Untreated asymptomatic bacteriuria in girls: I--Stability of urinary isolates.

OBJECTIVE--To assess the frequency of spontaneous changes of bacterial strains in patients with untreated asymptomatic bacteriuria. DESIGN--Retrospective analysis of samples from all patients with renal scarring and random sample of patients with normal kidneys. SETTING--Outpatient clinic for children with urinary tract infections. PATIENTS--54 Girls aged 3.3-15.5 years with untreated asymptomatic bacteriuria caused by Escherichia coli. INTERVENTION--None. END POINT--Change in bacterial strain. MEASUREMENTS AND RESULTS--Serotyping and electrophoretic analysis of sequential bacterial isolates, representing 151 patient years of untreated asymptomatic bacteriuria. A total of 24 changes of strain were identified. Eleven were related to medical interference such as treatment of other infections with antibiotics. CONCLUSIONS--Spontaneous changes of strain were uncommon, one change in 11.6 patient years, and thus are not a characteristic feature of the course of asymptomatic bacteriuria.     

In vitro growth of urinaryEscherichia coli related to siderophore production

Thirty seven strains ofEscherichia coli isolated from the urine of patients with acute symptomatic urinary tract infection were examined for siderophore production: hydroxamate (aerobactin) and phenolate (enterochelin). All the strains were found to produce varying amounts of enterochelin. With the chemical assay, 24.3% strains were aerobactin producers, while 43.2% were positive in the bio-assay. All the aerobactin producers carried the aerobactin receptor on their surface. Attempts to correlate siderophore production with growth in minimal and iron-depleted medium showed that there was a positive quantitative correlation between enterochelin production and growth of organisms under iron depletion. Aerobactin production failed to give an additional advantage of growth to strains producing enterochelin.     

Asymptomatic bacteriuria Escherichia coli strains: adhesins, growth and competition

Urinary tract infections (UTIs) affect millions of people each year. Escherichia coli is the most common organism associated with asymptomatic bacteriuria (ABU) in humans. Persons affected by ABU may carry a particular E. coli strain for extended periods of time without any symptoms. In contrast to uropathogenic E. coli (UPEC) that cause symptomatic UTI, very little is known about the mechanisms by which these strains colonize the urinary tract. Here, we have investigated the growth characteristics in human urine as well as adhesin repertoire of nine ABU strains; the ability of ABU strains to compete against the UPEC strain CFT073 was also studied. The different ABU strains displayed a wide variety of the measured characteristics. Half of the ABU strains displayed functional type 1 fimbriae while only one expressed functional P fimbriae. A good correlation between the growth rate of a particular strain and the survival of the strain in competition against CFT073 was observed. Our results support the notion that for strains with reduced capacity to express fimbriae, the ability to grow fast in human urine becomes crucial for colonization of the urinary tract.     

Virulence factors of Escherichia coli isolated from urine of diabetic women with asymptomatic bacteriuria: correlation with clinical characteristics

Since Escherichia coli isolated from compromised patients with symptomatic urinary tract infections (UTIs) express fewer virulence factors than those isolated from healthy controls, the question arises whether this is also the case for diabetic patients with asymptomatic bacteriuria (ASB). Polymerase chain reaction (PCR) assays were conducted on 111E. coli strains, isolated from the urine of diabetic women with ASB, using primers for the major subunit A and the G-adhesin (I, II, and III) of P fimbriae, type 1 fimbriae, S fimbriae, afimbrial adhesin, cytotoxic necrotizing factor (CNF), and aerobactin. Phenotypically, hemolysis, mannose-sensitive hemagglutination, mannose-resistant hemagglutination and O:K:H-serotypes were determined. Furthermore, we investigated the associations between virulence factors and patient characteristics (including deterioration of renal function). Type 1 fimbriae were the most prevalent virulence factor (86% by genotyping and 59% phenotypically). Except for a lower prevalence of known uropathogenic O-serotypes, we found the same number of virulence factors in our compromised patient group as listed in the literature in noncompromised patients with ASB. Certain virulence factors (type 1 and S fimbriae and CNF) of the causative E. colicorrelated with the risk of a decline in renal function. In conclusion, the number of virulence factors in E. coli isolated from the urine of diabetic women with ASB are comparable with the results found in other (noncompromised) patients with ASB. Furthermore, certain virulence factors of E. colimight contribute to a decline in renal function.     

Biofilm formation by asymptomatic and virulent urinary tract infectious Escherichia coli strains

Escherichia coli is the most common organism associated with asymptomatic bacteriuria (ABU) in humans. In contrast to uropathogenic E. coli (UPEC) that cause symptomatic urinary tract infection, very little is known about the mechanisms by which these strains colonize the urinary tract. Here, we have investigated the biofilm-forming capacity on abiotic surfaces of groups of ABU strains and UPEC strains in human urine. We found that there is a strong bias; ABU strains were significantly better biofilm formers than UPEC strains. Our data suggest that biofilm formation in urinary tract infectious E. coli seems to be associated with ABU strains and appears to be an important strategy used by these strains for persistence in this high-flow environment.     

Influence of ozone on the susceptibility ofEscherichia coli K1 to the bactericidal action of serum

The susceptibility to the bactericidal action of normal bovine serum of twenty twoEscherichia coli K1 strains, isolated from the urine of patients with urinary tract infections, was determined. Only four strains were resistant. Ozonization of bacterial suspensions enhanced the sensitivity of the strains to the action of both normal serum and a serum in which the alternative pathway of complement activation was thermally blocked.     

The role of E. coli adhesiveness in the pathogenesis and clinical course of urinary tract infections]

An infection with E. coli is the most frequent cause of the urinary infections in childhood. Virulence depends on several factors out of which a principal role is played by the adhesion of bacteria to the urinary tract epithelium. Such a property have E. coli strains with adherence mannose-positive fimbriae of type P with antigens recognizing and binding glycolipid receptors on epithelial cells in the urinary tract. Children with such infections owe their "sensitivity+" (10% of the population) to genetically determined large number o receptors binding E. coli strains. Incidence and clinical course of the urinary tract infections have been analysed in the group of 184 children. Moreover, sequelae of the urinary tract infections with E. coli have been analysed in dependence on E. coli strain characteristics, i.e. presence or absence of adherent fimbriae from cases of cystitis and significant asymptomatic bacteriuria. Considering pathogenesis of the urinary tract infections as the result of interactions between bacteria and host, antigenic properties of adherent fimbriae might be used for preparation of a vaccine preventing such infections.     

Adherence to kidney tissue ofEscherichia coli from humans with urinary tract infection

Twelve of 17 strains ofEscherichia coli from patients with proven upper uninary tract infection (UT) were shown to adhere to kidney tissue from rabbits. In contrast, only two of nine strains ofE. coli from humans with lower urinary tract infections (LT) adhered to kidney tissue. In addition, the effect of mannose on adherence to rabbit kidney tissue correlated with the effect of mannose on agglutination of guinea pig or human erythrocytes. Adherent isolated had pili demonstrated by electron microscopic studies and were more hydrophobic than were nonadherent isolates. These studies provide evidence that the surface of the bacillis is important in initiation of infection of kidney tissue byE. coli.     

Epidemiology of urinary tract diseases in general practice

During a one-year morbidity survey of urinary tract diseases in general practice 741 cases were diagnosed. Only about half of all the patients with symptoms of urinary tract infection had significant bacteriuria. In young women urinary tract infections and symptoms from the urinary tract without bacteriuria—in particular urethritis—were found to predominate. In middle-aged women, the urinary tract symptoms were ascribed increasingly to genital prolapse, while incidence of urolithiasis was the highest in any group, and urinary tract infections became less frequent. The prevalence of urinary tract infection showed another increase in elderly women, and recurrent/chronic pyelonephritis, which occurs with a steadily increasing prevalence throughout all age groups, became common.In younger male urological patients diseases with symptoms of urinary tract infection without bacteriuria were predominant, whereas prostatitis and urinary tract infections were less frequent. In middle-aged men, urolithiasis was especially frequent, while an increasing proportion of elderly men had prostatic hypertrophy, urinary tract infections, and recurrent/chronic pyelonephritis.