Analysis of urinary Escherichia coli isolates for ability to produce Shiga toxin

Hemolytic-uremic syndrome after Escherichia coli urinary tract infection in humans: systematic review of the literature

BACKGROUND

Intestinal infections caused by a shigatoxin-positive Escherichia coli (mostly of the serogroups O26, O45, O103, O111, O121, O145 and especially O157) are a common cause of hemolytic-uremic syndrome. Hemolytic-uremic syndrome was first linked with an E. coli urinary tract infection 40 years ago.

METHODS

We conducted a systematic review of the literature addressing the association between E. coli urinary tract infection and hemolytic-uremic syndrome.

RESULTS

For the final analysis, we retained 23 original reports published since 1979. Five unselected pediatric case series addressed the possible occurrence of hemolytic-uremic syndrome after an acute symptomatic E. coli urinary tract infection among 266 cases and found the mentioned association in 8 (3.0%) cases. We also found 28 individual cases (17 females and 11 males) of hemolytic-uremic syndrome preceded by an E. coli urinary tract infection: 16 children aged from 2 days to 6.0 years and 12 adults aged from 22 to 75 years. Testing for shigatoxin, performed in 19 cases, was positive in 15 cases. E. coli serotyping was performed in 18 cases: testing for serotype O157, O103 and O145 was positive in one, one and two cases, respectively, while testing for serotype O26, O45, O111 and O121 was always negative.

CONCLUSIONS

Hemolytic-uremic syndrome rarely occurs after an acute E. coli urinary tract infection. It affects both children and adults and is mostly caused by germs that are shigatoxin-positive.

Characterization of urinary tract infection-associated Shiga toxin-producing Escherichia coli

Enterohemorrhagic Escherichia coli (EHEC), a subgroup of Shiga toxin (Stx)-producing E. coli (STEC), is a leading cause of diarrhea and hemolytic-uremic syndrome (HUS) in humans. However, urinary tract infections (UTIs) caused by this microorganism but not associated with diarrhea have occasionally been reported. We geno- and phenotypically characterized three EHEC isolates obtained from the urine of hospitalized patients suffering from UTIs. These isolates carried typical EHEC virulence markers and belonged to HUS-associated E. coli (HUSEC) clones, but they lacked virulence markers typical of uropathogenic E. coli. One isolate exhibited a localized adherence (LA)-like pattern on T24 urinary bladder epithelial cells. Since the glycosphingolipids (GSLs) globotriaosylceramide (Gb3Cer) and globotetraosylceramide (Gb4Cer) are well-known receptors for Stx but also for P fimbriae, a major virulence factor of extraintestinal pathogenic E. coli (ExPEC), the expression of Gb3Cer and Gb4Cer by T24 cells and in murine urinary bladder tissue was examined by thin-layer chromatography and mass spectrometry. We provide data indicating that Stxs released by the EHEC isolates bind to Gb3Cer and Gb4Cer isolated from T24 cells, which were susceptible to Stx. All three EHEC isolates expressed stx genes upon growth in urine. Two strains were able to cause UTI in a murine infection model and could not be outcompeted in urine in vitro by typical uropathogenic E. coli isolates. Our results indicate that despite the lack of ExPEC virulence markers, EHEC variants may exhibit in certain suitable hosts, e.g., in hospital patients, a uropathogenic potential. The contribution of EHEC virulence factors to uropathogenesis remains to be further investigated.

Heteropathogenic virulence and phylogeny reveal phased pathogenic metamorphosis in Escherichia coli O2:H6

Extraintestinal pathogenic and intestinal pathogenic (diarrheagenic) Escherichia coli differ phylogenetically and by virulence profiles. Classic theory teaches simple linear descent in this species, where non-pathogens acquire virulence traits and emerge as pathogens. However, diarrheagenic Shiga toxin-producing E. coli (STEC) O2:H6 not only possess and express virulence factors associated with diarrheagenic and uropathogenic E. coli but also cause diarrhea and urinary tract infections. These organisms are phylogenetically positioned between members of an intestinal pathogenic group (STEC) and extraintestinal pathogenic E. coli. STEC O2:H6 is, therefore, a 'heteropathogen,' and the first such hybrid virulent E. coli identified. The phylogeny of these E. coli and the repertoire of virulence traits they possess compel consideration of an alternate view of pathogen emergence, whereby one pathogroup of E. coli undergoes phased metamorphosis into another. By understanding the evolutionary mechanisms of bacterial pathogens, rational strategies for counteracting their detrimental effects on humans can be developed.

Adult hemolytic-uremic syndrome associated with urosepsis due to Shigatoxin-producing Escherichia coli O138:H-

We report the case of a 62-year-old man without prodromal symptoms who developed a hemolytic-uremic syndrome (HUS) one week after the diagnosis of an acute bacteremic urinary infection (UTI). In this patient, the E. coli isolated in blood cultures was a non-O157:H7 Shigatoxin-producing strain that could subsequently be identified as O138:H-. This is a strain that is normally found in pigs and that has never been isolated in humans previously. UTI-related HUS is a rare event, as until now, only 14 pediatric and 3 adult cases have been reported. Indeed, this new case, besides its interesting microbiological aspects, should heighten our awareness of UTI-related HUS as a rare but real condition, not only in young children but also in adult patients. This should emphasize the necessity to search actively for other sources of Shigatoxin-producing E. coli in patients presenting with HUS without gastrointestinal symptoms.

Fim operon variation in the emergence of Enterohemorrhagic Escherichia coli: an evolutionary and functional analysis

Fim operons were examined to illuminate the emergence of Escherichia coli O157:H7 from the less-virulent E. coli O55:H7. A fim invertible element deletion occurred only after O157:H7 descended from O55:H7, and after sorbitol nonfermenting O157 diverged. Type 1 pili nonexpression correlates with this deletion in all enterohemorrhagic E. coli (EHEC) tested. An N135K FimH mutation in the two most evolved O157:H7 clusters is not found in other EHEC. These data refine the evolutionary history of an emerging pathogen.

Characterization of four novel genomic regions of uropathogenic Escherichia coli highly associated with the extraintestinal virulent phenotype: a jigsaw puzzle of genetic modules

Extraintestinal pathogenic Escherichia coli (ExPEC) are a major cause of urinary tract infections, sepsis, and neonatal meningitis. A variety of virulence factors in these strains is encoded by mobile genetic elements, such as transposons or pathogenicity islands (PAIs). Using subtractive cloning of ExPEC genomes, we recently detected short DNA fragments, which were significantly associated with the extraintestinal virulent phenotype. In this study, we identified four novel genomic DNA regions of the highly virulent uropathogenic E. coli strain JS299 carrying these previously identified DNA fragments. Characterization of the partial sequences of the genomic DNA regions revealed complex DNA arrangements with variable genetic compositions regarding the G+C contents and codon usage patterns. The prevalence of 15 previously uncharacterized genes was determined in a collection of clinical ExPECs and commensal E. coli strains by means of DNA microarray analyses. From this, 13 novel DNA sequences were demonstrated to be significantly associated with extraintestinal virulent strains, and thus may represent new virulence traits. Beside genes predicted to play a role in metabolic functions, such as sucrose utilization (scr), we identified DNA sequences shared by both ExPEC and enteropathogenic E. coli (EPEC). These sequences were significantly more prevalent among ExPECs when compared to commensal E. coli isolates. Our results support the idea of a considerable genetic variability among ExPEC strains and suggest that the novel genomic determinants described in this study may contribute to the ExPEC virulence.

Non-enteropathic hemolytic uremic syndrome: causes and short-term course

BACKGROUND

Nondiarrheal or Streptococcus pneumoniae-related hemolytic uremic syndrome (HUS) represents a heterogeneous group of disorders. This study was performed to: (1) describe the current incidence, causes, demographic features, hospital courses, and short-term outcomes of non-enteropathic HUS; (2) compare findings in patients with non-enteropathic HUS with those obtained from a contemporaneous cohort of children with enteropathic or diarrhea-associated HUS (D+ HUS) diagnosed and treated at the same clinical sites; and (3) identify clinical or laboratory features that differentiate these 2 groups and predict disease severity and the short-term outcome in patients with non-enteropathic HUS.

METHODS

Data were collected from patients screened between 1997 and 2001 for enrollment in a multicenter trial of SYNSORB Pk (SYNSORB Biotech Inc, Calgary, Alberta, Canada) in D+ HUS, but who were ineligible because of lack of a diarrhea prodrome. The following features were recorded: age; sex; ethnicity; prodromal symptoms; cause; nadir values for hemoglobin, hematocrit, and platelet count; use of dialysis; and length of hospitalization.

RESULTS

Twenty-seven of 247 children with HUS had non-enteropathic HUS (11%). Twenty-four patients (15 boys, 9 girls), whose medical records were complete and available for review, comprise the study cohort. Mean age at onset was 4.2 +/- 0.9 (SE) years. Infection caused by S pneumoniae was diagnosed in 9 patients (38%). Dialysis was performed in 17 patients (71%) for 40 +/- 27 days. Median length of hospitalization was 22 days (range, 2 to 71 days). Children with S pneumoniae-related HUS had a longer hospital stay than those with other causes of non-enteropathic HUS, but all patients with S pneumoniae-related HUS recovered kidney function. Dialysis therapy was required more often (17 of 24 versus 59 of 145 children; P = 0.025) and hospital stays were longer (median, 22 versus 9 days; P = 0.002) in children with non-enteropathic HUS compared with patients with D+ HUS who were enrolled in the SYNSORB Pk clinical trial.

CONCLUSION

(1) The incidence of non-enteropathic HUS is approximately one tenth that of D+ HUS; (2) patients with non-enteropathic HUS require dialysis therapy more often and are hospitalized more than twice as long during the acute episode compared with those with D+ HUS; (3) infection caused by S pneumoniae accounts for nearly 40% of cases of non-enteropathic HUS; and (4) although S pneumoniae-related HUS is associated with a less favorable short-term course than other types of non-enteropathic HUS or D+ HUS, the long-term prognosis for recovery of renal function appears to be good in these patients.