Urinary Tract Infection Strains Research Articles

Is Escherichia coli urinary tract infection a zoonosis? Proof of direct link with production animals and meat

Recently, it has been suggested that the Escherichia coli causing urinary tract infection (UTI) may come from meat and animals. The purpose was to investigate if a clonal link existed between E. coli from animals, meat and UTI patients. Twenty-two geographically and temporally matched B2 E. coli from UTI patients, community-dwelling humans, broiler chicken meat, pork, and broiler chicken, previously identified to exhibit eight virulence genotypes by microarray-detection of approximately 300 genes, were investigated for clonal relatedness by PFGE. Nine isolates were selected and tested for in vivo virulence in the mouse model of ascending UTI. UTI and community-dwelling human strains were closely clonally related to meat strains. Several human derived strains were also clonally interrelated. All nine isolates regardless of origin were virulent in the UTI model with positive urine, bladder and kidney cultures. Further, isolates with the same gene profile also yielded similar bacterial counts in urine, bladder and kidneys. This study showed a clonal link between E. coli from meat and humans, providing solid evidence that UTI is zoonosis. The close relationship between community-dwelling human and UTI isolates may indicate a point source spread, e.g. through contaminated meat.

Rates of Mutation and Host Transmission for an Escherichia coli Clone over 3 Years

Although over 50 complete Escherichia coli/Shigella genome sequences are available, it is only for closely related strains, for example the O55:H7 and O157:H7 clones of E. coli, that we can assign differences to individual evolutionary events along specific lineages. Here we sequence the genomes of 14 isolates of a uropathogenic E. coli clone that persisted for 3 years within a household, including a dog, causing a urinary tract infection (UTI) in the dog after 2 years. The 20 mutations observed fit a single tree that allows us to estimate the mutation rate to be about 1.1 per genome per year, with minimal evidence for adaptive change, including in relation to the UTI episode. The host data also imply at least 6 host transfer events over the 3 years, with 2 lineages present over much of that period. To our knowledge, these are the first direct measurements for a clone in a well-defined host community that includes rates of mutation and host transmission. There is a concentration of non-synonymous mutations associated with 2 transfers to the dog, suggesting some selection pressure from the change of host. However, there are no changes to which we can attribute the UTI event in the dog, which suggests that this occurrence after 2 years of the clone being in the household may have been due to chance, or some unknown change in the host or environment. The ability of a UTI strain to persist for 2 years and also to transfer readily within a household has implications for epidemiology, diagnosis, and clinical intervention.

Serotyping of Proteus mirabilis clinical strains based on lipopolysaccharide O-polysaccharide and core oligosaccharide structures

The aim of this work was to serotype Proteus mirabilis urinary tract infection (UTI) strains based on chemically defined O-antigens with the use of two clinical collections from Sweden and Poland consisting of 99 and 24 UTI strains, respectively. A simple two-step serotyping scheme was proposed using enzyme immunoassay with heat-stable surface antigens of Proteus cells and immunoblotting with isolated lipopolysaccharides (LPSs). Using polyclonal anti-P. mirabilis rabbit antisera, 50 Swedish and 8 Polish strains were classified into serogroups O10, O38, O36, O30, O17, O23, O9, O40, O49, O27, O5, O13, O24, O14, and O33. From the Swedish strains, 10 belonged to serogroup O10 and five to each of serogroups O38, O36, and O9. Therefore, none of the O-serogroups was predominant. The majority of the serotyped clinical strains possess acidic O-antigens containing uronic acids and various acidic non-carbohydrate substituents. In immunoblotting, antisera cross-reacted with both O-antigen and core of LPSs. The core region of 19 LPSs bound a single serum, and that of 12 LPSs bound more than two sera. Following bioinformatic analysis of the available sequences, a molecular approach to the prediction of Proteus core oligosaccharide structures was proposed. The identification of the core type of P. mirabilis R110, derived from a serogroup O3 wild strain, using restriction fragments length polymorphism analysis of galacturonic acid transferase is shown as an example. In summary, the most frequent O-serogroups among P. mirabilis UTI stains were identified. The diversity of serological reactions of LPSs is useful for serotyping of P. mirabilis clinical isolates. A possible role of the acidic components of O-antigens in UTI is discussed.

Clinical and microbiological characteristics of Klebsiella pneumoniae isolates causing community-acquired urinary tract infections

Klebsiella pneumoniae is the second most common species causing urinary tract infections (UTI). However, the host factors and virulence genes of K. pneumoniae related to UTI are poorly understood. The aim of this study was to analyze the capsular phenotype and virulence genes of K. pneumoniae isolates and host factors potentially relevant to community-acquired UTI. Fifty-four K. pneumoniae isolates from patients with community-acquired UTI, 76 isolates from healthy adults, and 29 from patients with community-acquired pneumonia were compared. The virulence genes (rmpA, magA, uge, and wabG) and serotype (K1, K2, K5, K20, K54, or K57) were characterized by polymerase chain reaction (PCR). The modified string test was used to determine the hypermucoviscosity. Diabetes mellitus was the most frequent underlying disease among UTI patients (53.7%, 29/54). No predominant K serotype was found in UTI strains. The hypermucoviscosity phenotype and rmpA gene were more often found in UTI isolates than in those from healthy adults (27.8 vs. 2.6%, P < 0.01; 29.6 vs. 11.8%, P < 0.01, respectively), whereas no significant difference in the frequency of magA, uge, wabG, or serotype genes was found. The prevalence of rmpA was significantly lower in isolates from patients with immunosuppression, chronic renal insufficiency, and urinary tract obstruction. Multivariate analysis showed that immunosuppression was negatively associated with the prevalence of rmpA. Hypermucoviscosity was highly correlated with the presence of the rmpA gene in UTI strains, and rmpA may have a role in community-acquired UTI, especially in hosts without immunosuppression.

Bacteriocin synthesis in uropathogenic and commensal Escherichia coli: colicin E1 is a potential virulence factor

BackgroundBacteriocin production is an important characteristic of E. coli strains of human origin. To date, 26 colicin and 9 microcin types have been analyzed on a molecular level allowing molecular detection of the corresponding genes. The production incidence of 29 bacteriocin types and E. coli phylogroups were tested in a set of 361 E. coli strains isolated from human urinary tract infections (UTI) and in 411 control strains isolated from feces of patients without bacterial gut infection.ResultsProduction of 17 and 20 individual bacteriocin types was found in the UTI and control strains, respectively. Microcin H47 encoding determinants were found more often among UTI strains compared to controls (37.9% and 27.0% respectively, p = 0.02) and strains producing microcin H47 belonged predominantly to phylogroup B2 when compared to other bacteriocin producers (67.4% and 36.7%, respectively; p < 0.0001). Producers of 3 or more identified bacteriocin types were more common in the UTI group (20.0% compared to 12.4% in controls, p = 0.03). In the UTI strains, there was a markedly higher number of those producing colicin E1 compared to controls (22.1% to 10.2%, respectively, p = 0.0008). Moreover, colicin E1 production was more common in the UTI bacteriocinogenic strains with multi-producer capabilities. As shown by Southern blotting, pColE1 DNA was not recognized by the ColIa probe and vice versa suggesting that pColE1 was independently associated with pColIa in UTI strains.ConclusionE. coli strains isolated from human urinary tract infections showed increased incidence of microcin H47 and colicin E1 production, respectively. Moreover, colicin E1 itself appears to be a potentially important virulence factor of certain uropathogenic E. coli strains.

Investigation of Positive Streptococcus pneumoniae Urinary Antigen Test Results in a Korean University Hospital

Background: The Streptococcus pneumoniae urinary antigen test (SPUAT) (Binax Now, USA) was developed for detecting polysaccharide C in urine samples for rapid diagnosis of pneumococcal pneumonia, the most common cause of community-acquired pneumonia (CAP). To validate positive results of these tests, we retrospectively investigated all positive results obtained from the emergency room of a Korean university hospital among patients with suspected CAP. Methods: One hundred twenty-three positive SPUAT results were abstracted and analyzed from the authors' laboratory information system among the SPUAT results performed from 1,143 pneumonic patients admitted from the emergency room of a university hospital between 2007 and 2008. Medical records, including conventional microbiologic analysis results, were reviewed in detail for all positive test results. Results: Among 123 patients with the positive SPUAT results, 24 patients were excluded due to hospitalization history during the preceding month. Nine of 99 patients (9.1%) with suspected CAP had confirmed pneumococcal pneumonia upon conventional sputum or blood culture. Thirty-five positive results (35.4%) showed other microorganisms upon conventional methods, which might be due to possible cross-reactivity. Among those, 23 positive results were considered bacterial pneumonic agents, and 12 positive results were regarded as urinary tract infection strains or contaminating agents. Fifty-five positive SPUAT results (55.6%) showed negative conventional microbiologic growth, and some positive SPUAT results might be caused by true pneumococcal infection although without cultural evidence. Conclusion: Our retrospective study demonstrated that a positive SPUAT result typically does not agree well with conventional culture methods, suggesting that the value of a positive SPUAT result in etiology determination may be limited under practical conditions in a university hospital. (Korean J Clin Microbiol 2010;13:14-18)

Comparative analysis of antibiotic resistance and phylogenetic group patterns in human and porcine urinary tract infectious Escherichia coli

Urinary tract infections (UTIs) are one of the most common infectious diseases in humans and domestic animals such as pigs. The most frequent infectious agent in such infections is Escherichia coli. Virulence characteristics of E. coli UTI strains range from highly virulent pyelonephritis strains to relatively benign asymptomatic bacteriuria strains. Here we analyse a spectrum of porcine and human UTI E. coli strains with respect to their antibiotic resistance patterns and their phylogenetic groups, determined by multiplex PCR. The clonal profiles of the strains differed profoundly; whereas human strains predominantly belonged to clonal types B2 and D, these were not seen among the porcine strains, which all belonged to the E. coli clonal groups A and B1. Contrary to the human strains, the majority of the porcine strains were multidrug resistant. The distinct profiles of the porcine strains suggest selective pressure due to extensive antibiotic use.

Association analysis between Intragenomic Gene Conversions and pathogenicity in genomes of Escherichia coli and Shigella spp.: a scientific workflow approach

The RECOMBFLOW scientific workflow system was used to test a previously suggested hypothesis that pathogenic Escherichia coli have more Intragenomic Gene Conversions (IGC) than non-pathogenic strains. Although some pathogens (O157:H7 and some Urinary Tract Infection (UTI) strains) had high IGC, two UTI strains and six Shigella (pathogens in the E. coli clade) were near non-pathogenic E. coli levels. Functional bacterial gene families with IGC in >4 genomes included efflux pumps, L-serine deaminases, FeS binding subunits of oxidoreductases and glutamate synthase, porins and related membrane proteins, Rhs elements, and L-ribulose-5-phosphate-4-epimerase. Shigella had lower IGCs in these families than non-pathogenic E. coli.

Escherichia coli colonizing the neurogenic bladder are similar to widespread clones causing disease in patients with normal bladder function

Clonal typing of neurogenic clones. To determine whether neurogenic clones carried over weeks in the urine of asymptomatic children with neurogenic bladder were similar to known uropathogenic clones associated with disease. Michigan State University; VA Medical Center, Minneapolis, MN, USA. Escherichia coli isolates from the urine of 15 children previously followed were typed by multilocus sequence typing and compared to 2 human pyelonephritis genome strains, 29 pediatric or adult symptomatic urinary tract infection strains, 15 pediatric asymptomatic bacteriuria strains, 6 animal urinary tract infection strains and a neonatal meningitis-septicemia prototype K1 strain. Phylotypes and virulence genotypes were determined using PCR. Twenty-nine E. coli isolates were classified into 15 clones. Six of 15 clones were the same sequence type or a close relative to a clone that caused disease in a human or animal. These clones were considered uropathogens. The remaining nine clones were not closely related to a clone that caused disease and were considered commensal clones. Uropathogens were predominantly group B2, exhibited more virulence genes and were carried for more weeks in the neurogenic bladder compared to commensal clones. Nine of 15 children carried one or more uropathogenic clones; 4 children carried one or more commensal clones and 2 children carried both uropathogenic and commensal clones. Children with neurogenic bladder most commonly carried commensal clones. Uropathogenic clones were associated with prolonged carriage, however, carriage was not associated with symptomatic disease or deterioration of the upper urinary tract.

The ferric yersiniabactin uptake receptor FyuA is required for efficient biofilm formation by urinary tract infectious Escherichia coli in human urine

Urinary tract infection (UTI) is the most common infection in patients with indwelling urinary catheters, and bacterial biofilm formation is a major problem in this type of infection. Escherichia coli is responsible for the large majority of UTIs. Free iron is strictly limited in the human urinary tract and there is fierce competition between the host and infectious bacteria for this essential metal. Urinary tract infectious E. coli have highly efficient mechanisms of iron acquisition, one of which is the yersiniabactin system. The fyuA gene, encoding the yersiniabactin receptor, is one of the most upregulated genes in biofilm; it was upregulated 63-fold in the E. coli UTI strain VR50. FyuA was found to be highly important for biofilm formation in iron-poor environments such as human urine. Mutants in fyuA show aberrant biofilm formation and the cells become filamentous; a VR50fyuA mutant showed a 92 % reduction in biofilm formation in urine flow-cell chambers compared with the wild-type. The FyuA/yersiniabactin system is known to be important for virulence. Here we demonstrate a direct link between FyuA and biofilm formation in iron-poor environments. We also show that the availability of iron greatly influences UTI strains' ability to form biofilm.

Expression of cellulose and curli fimbriae by Escherichia coli isolated from the gastrointestinal tract

Escherichia coli colonizes the gastrointestinal tract of humans; however, little is known about the features of commensal strains. This study investigated whether expression of the biofilm extracellular matrix components cellulose and curli fimbriae is found among commensal isolates. Fifty-two E. coli strains were isolated from faecal samples and, as a control, 24 strains from urinary tract infections were also used. Faecal isolates were characterized by serotyping and phylogenetically grouped by PCR. The genotype was determined by PFGE and the presence of virulence factors was assessed. Co-expression of cellulose and curli fimbriae at 28 degrees C and 37 degrees C was typical for faecal isolates, while urinary tract infection strains typically expressed the extracellular matrix components at 28 degrees C only. Knockout studies in a representative faecal isolate revealed that the response regulator CsgD regulated cellulose and curli fimbriae, as found previously in Salmonella enterica. In contrast to S. enterica, at 37 degrees C pellicle formation occurred in the absence of cellulose and curli fimbriae. The gastrointestinal tract represents a source of biofilm-forming bacteria, which can spread to susceptible sites.

Infectivity of Hepatic Strain Klebsiella pneumoniae in Diabetic Mice

Besides urinary tract infection (UTI) and pneumonia, increased severe liver abscesses caused by Klebsiella pneumoniae (KP), especially in diabetic patients, have been observed in infections acquired in hospitals. This indicates that different KP strains with higher virulence have emerged in recent years. Our goal was to investigate the infectivity of KP isolates in mice from liver abscess or UTI patients. Mice were injected with streptozotocin to induce diabetes. Male ICR mice were infected with KpU1 (UTI strain CG3 for survival experiment only) and KpL1 (liver abscess strain CG5) by tail-vein injection of 5 x 10(4) colony-forming units (CFU) bacterial suspension. The mice survival rates, cytokine level by enzyme-linked immunosorbent assay (ELISA), and bacterial presence in liver tissue by Giemsa stain were examined. The survival rates for the KpL1-infected animals were 28% and 0% in normal and diabetic groups, respectively, whereas, for the KpU1-infected mice, the rates were 100% and 75% during a 30-day observation. Nonsurviving KpL1-infected mice showed > 10(5) bacteria/ml blood and the bacteria appeared in the liver sinus area and inside liver cells. The KpL1-infected mice showed a tendency to increase the blood interleukin 1beta (IL-1beta) level in both nondiabetic and diabetic groups, whereas the tumor necrosis factor-alpha (TNF-alpha) level was significantly decreased in the KpL1-infected diabetic mice (P = 0.002). In conclusion, the KP strain from liver abscess showed a greater virulence in mice than the KP from UTI and was more virulent in diabetic than in nondiabetic mice. The infection with KP from liver abscess significantly decreased the blood TNF-alpha level in diabetes mellitus (DM) mice and the blood IL-1beta level tended to increase in both infected nondiabetic and diabetic groups. High blood bacterial count and appearance of bacteria in liver sinus and cells usually contribute to death of the animals.

Designer Antibacterial Peptides Kill Fluoroquinolone-Resistant Clinical Isolates

A significant number of Escherichia coli and Klebsiella pneumoniae bacterial strains in urinary tract infections are resistant to fluoroquinolones. Peptide antibiotics are viable alternatives although these are usually either toxic or insufficiently active. By applying multiple alignment and sequence optimization steps, we designed multifunctional proline-rich antibacterial peptides that maintained their DnaK-binding ability in bacteria and low toxicity in eukaryotes, but entered bacterial cells much more avidly than earlier peptide derivatives. The resulting chimeric and statistical analogues exhibited 8-32 microg/mL minimal inhibitory concentration efficacies in Muller-Hinton broth against a series of clinical pathogens. Significantly, the best peptide, compound 5, A3-APO, retained full antibacterial activity in the presence of mouse serum. Across a set of eight fluoroquinolone-resistant clinical isolates, peptide 5 was 4 times more potent than ciprofloxacin. On the basis of the in vitro efficacy, toxicity, and pharmacokinetics data, we estimate that peptide 5 will be suitable for treating infections in the 3-5 mg/kg dose range.

TRACING THE ORIGIN OF MULTI‐DRUG RESISTANT (MDR) ESCHERICHIA COLI INFECTIONS FROM URINARY CATHETERS IN ICU CANINE PATIENTS

Introduction: Urinary tract infections (UTIs) in dogs with urinary catheters in intensive care units (ICUs) are frequent. Historically, multi‐drug resistant (MDR) Escherichia coli account for about 10% of the UTIs. The objectives of this study were to determine the frequency of E. coli infections and of MDR E. coli in dogs with UTIs in our ICU, and to assess whether the MDR E. coli were community‐acquired or nosocomial in origin.Methods: Over a 1‐year period, rectal swabs were taken from all dogs in the ICU on the day of admission (D0) and on days 3 (D3), 6 (D6), 9 (D9) and 12 (D12). Urine was collected on these days from dogs with an indwelling urinary catheter (n=190). Rectal swabs and urine were routinely cultured. E. coli isolates were identified by biochemical tests. Using NCCLS guidelines, antibiotic susceptibility testing was done by disk diffusion method on fecal and urinary E. coli isolates. Twelve antimicrobial agents were used: nalidixic acid, enrofloxacin, cephalothin, cefoxitin, cefotaxime, ceftiofur, trimethoprim‐sulfa, chloramphenicol, gentamicin, tetracycline, ampicillin, and amoxicillin/clavulanate. Pulsed‐field gel electrophoresis (PFGE) was used to compare MDR E. coli UTI strains with fecal E. coli strains from the same patient and with MDR fecal E. coli from patients that were adjacent to, or housed in the same cages.Results: E. coli was cultured from 12 (48%) of 25 UTIs. Two of the E. coli were MDR. For one dog, PFGE showed no similarities among fecal E. coli and the urinary MDR E. coli isolates from the patient or between these isolates and fecal E. coli from a dog housed in the same kennel on the previous day. The MDR E. coli UTI was likely acquired prior to admission to the ICU, as it was present on D0. For the other dog, PFGE showed genetic similarity but not complete identity between the D3 MDR E. coli urinary isolate and the D3, D6, D9 fecal MDR isolates. This suggests that the UTI originated with the fecal E. coli. Using selective plates, fecal MDR E. coli were not found on D0. Selection of the MDR strain in the intestine by the use of antibiotics occurred while the dog was in the ICU and possibly led to the UTI.Conclusions: Multi‐drug resistant E. coli accounted for 2 of 12 E. coli UTIs in dogs in the ICU over a 1‐year period. Genotyping showed that one of the two MDR E. coli infections could possibly be of nosocomial origin.

Survey for virulence determinants among Enterococcus faecalis isolated from different sources.

A collection of Enterococcus faecalis strains from clinical isolates, healthy individuals and the environment was screened for the presence of virulence factor genes, such as those for collagen-binding protein (ace), endocarditis antigen (efaA), haemolysin activator (cylA), gelatinase (gelE), aggregation substances (asa1 and asa373), a surface protein (esp) and two novel putative surface antigens (EF0591 and EF3314). Apart from some genes that were present in all strains (ace, efaA and EF3314), the gelE gene was the most common factor, although its presence did not correlate with its expression. The genes that encode Esp and CylA were never detected in endocarditis isolates, whereas an association was noted between the esp gene and isolates from urinary tract infection (UTI) and bacteraemia. An aggregation substance gene was always present in commensal strains. As for gelatinase, the presence of the cylA and asa genes did not correlate completely with their phenotypic expression. Generally, isolates from endocarditis, biliary stents and the environment were equipped with fewer virulence factors than isolates from other sources. UTI strains possessed the highest number of factors.

Production of Cytolethal Distending Toxins by Pathogenic Escherichia coli Strains Isolated from Human and Animal Sources: Establishment of the Existence of a New cdt Variant (Type IV)

Three types of cytolethal distending toxin (CDT), namely, CDT-I, CDT-II, and CDT-III, have been described in Escherichia coli. Using primers designed for the detection of sequences common to the cdtB genes, we analyzed by PCR a set of 21 CDT-producing E. coli strains of intestinal and extraintestinal origins isolated from human and different animal species in several European countries and in the United States. On the basis of the existing differences in the cdtB genes, cdt-I-, cdt-II-, and cdt-III-specific primer pairs were designed and used for cdt typing. These new primers successfully differentiated all of the previously described cdt genes. Six strains proved to be cdt-I; eight strains proved to be cdt-III. However, none of the type I-, II-, and III-specific primers generated amplicons from six CDT(+) strains, suggesting the existence of a new cdt variant. Sequence analysis of the amplicons from two untypeable genes confirmed the existence of a new cdt variant that we called cdt-IV. Using the new specific primers, cdt-IV was detected in human, porcine, and poultry strains of intestinal and extraintestinal origins. To validate all sets of cdt specific primers, a group of 353 human E. coli strains isolated in Hungary was then investigated for the presence of cdt genes. This included 190 strains isolated from patients with urinary tract infections (UTI), 51 strains isolated from other (nonurinary) extraintestinal infections, and 112 intestinal strains isolated from healthy individuals. Of 190 UTI strains, 15 (7.9%) had cdt genes. Of 51 non-UTI extraintestinal strains 3 (5.9%) contained the cdt gene, and 1 (0.9%) of 112 healthy intestinal strains was PCR positive. Five strains proved to be cdt-I, and fourteen strains proved to be cdt-IV. The CDT-producing extraintestinal strains belonged to a wide variety of serogroups, including O2, O6, O75, and O170. In conclusion, we have developed a new PCR typing system for CDT able to detect a new CDT variant present in pathogenic E. coli strains obtained from animals and humans.

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.

Evolutionary relationships among pathogenic and nonpathogenic Escherichia coli strains inferred from multilocus enzyme electrophoresis and mdh sequence studies.

Within the species Escherichia coli, there are commensal strains and a variety of pathogenic strains, including enteropathogenic E. coli (EPEC), enterohemorrhagic E. coli (EHEC), enterotoxigenic E. coli (ETEC), enteroinvasive E. coli (EIEC), and urinary tract infection (UTI) strains. The pathogenic strains are identified by serotype and by possession of specific virulence determinants (toxins and adhesions, etc.) encoded by either monocistronic genes, plasmids, or pathogenicity islands. Although there are studies on the relationships between selected pathogenic strains, the relatedness among the majority of the pathogenic forms to each other, to commensal E. coli, and to the genus Shigella (which has often been suggested to be part of E. coli) has not been determined. We used multilocus enzyme electrophoresis (MLEE) at 10 enzyme loci and the sequence of the mdh housekeeping gene to study the genetic relationships of pathogenic E. coli strains (including Shigella clones), namely, 5 EPEC strains (serotypes O111 and O55), 3 EHEC strains (serotype O157), 6 ETEC strains (serotypes O78, O159, and O148), 5 EIEC strains (serotypes O124, O28, and O112), and 13 Shigella strains representing clones Flexneri, Dysenteriae, Boydii, and Sonnei, to commensal E. coli strains. Both the MLEE and mdh sequence trees reveal that EPEC, EHEC, ETEC, EIEC, and UTI strains are distributed among the ECOR set groups, with no overall clustering of EPEC, ETEC, EIEC, or UTI strains. The genus Shigella is shown to comprise a group of closely related pathogenic E. coli strains. Six pathogenic strains, i.e., M502 (EIEC; O112ac:NM), M503 (EPEC; O111:H12), M526 (ETEC; O159:H4), M522 (EPEC; O111ac:H12), M524 (ETEC; O78:H11), and M506 (ETEC; O78:H11), were found to have mdh sequences identical to those of five ECOR group A strains (ECOR5, ECOR10, ECOR14, ECOR6, and K-12). All 11 strains are closely related by MLEE. The results indicate that pathogenic strains of E. coli do not have a single evolutionary origin within E. coli but have arisen many times. The results also suggest the possibility that any E. coli strain acquiring the appropriate virulence factors may give rise to a pathogenic form.

Distribution of drb genes coding for Dr binding adhesins among uropathogenic and fecal Escherichia coli isolates and identification of new subtypes

The Dr family of related adherence structures, some fimbriated and others afimbriated, bind to decay-accelerating factor molecules on human cells. Dr is associated with recurring urinary tract infection (UTI), but the distribution of Dr subtypes among uropathogenic Escherichia coli causing UTI among otherwise healthy women has yet to be described. A total of 787 UTI and fecal E. coli isolates from college women were screened for the presence of Dr sequences (drb). Fifteen percent of UTI strains were drb positive, compared to 5% of fecal strains. The adhesin (E gene) subtype of each drb-positive strain was determined by type-specific PCR followed by restriction enzyme analysis. Among 78 drb-positive strains, we found 14 (18%) afaE1, 1 (1.3%) afaE2, 1 (1.3%) afaE3, 9 (12%) draE, 9 (12%) draE-afaE3 hybrid, 1 (1.3%) daaE, 32 (41%) afaE5, 4 (5.1%) F131 E gene-like, and 7 untypeable strains. All untypeable E genes were cloned and sequenced, revealing four additional new classes of E genes, including two similar to the previously identified nonfimbrial E series. While a great range of diversity exists among the E genes, restriction fragment length polymorphism analysis demonstrated that all of these drb operons share a highly conserved gene structure. The most common subtype, afaE5, occurred three times as often among UTI than fecal strains. Over half of the drb-positive strains and 80% of those positive for afaE5 have the same virulence signature (positive for aer, kpsMT, ompT, and fim), suggesting an association of this profile with UTI pathogenesis.

Virulence-associated factors in Escherichia coli strains isolated from children with urinary tract infections.

One hundred and sixty-eight strains of Escherichia coli were isolated from cases of pyelonephritis (24) and lower urinary tract infections (UTI) (144) from hospitalised and outpatient children up to 2 years old. These strains were investigated for the expression of P fimbriae (PF), mannose-resistant and mannose-sensitive haemagglutination, cell-surface hydrophobicity, serum resistance and the production of alpha-haemolysin (AH), colicins and aerobactin. PF, AH, aerobactin production and serum resistance were significantly more frequent amongst strains expressing mannose-resistant haemagglutination. PF and AH production was significantly more frequent in pyelonephritogenic strains than in lower UTI strains. Serotypes O6 and O112 were isolated most frequently and plasmids were found in the majority of strains tested.