non-O157 Enterohemorrhagic Escherichia Coli Research Articles

Hemolytic-uremic syndrome surveillance to monitor trends in infection with Escherichia coli O157 and non-O157 enterohemorrhagic E. coli in Austria.

Austrian data underline that relying on the number of enterohemorrhagic Escherichia coli (EHEC) O157 strains isolated from clinical specimens does not allow assessment of the actual incidence of EHEC infections. A hospital-based system for identification of hemolytic-uremic syndrome cases based on voluntary cooperation was established in 1995 and provides information needed to monitor trends in the incidence of O157 and non-O157 EHEC infections.

The role of virulence factors in enterohemorrhagic Escherichia coli (EHEC)--associated hemolytic-uremic syndrome.

Enterohemorrhagic Escherichia coli (EHEC) are the most common cause of postdiarrheal hemolytic-uremic syndrome (HUS). The most important EHEC serotype implicated worldwide is O157:H7. However, several so-called non-O157 EHEC serotypes have emerged. After a mean incubation period of 3 days, patients develop watery diarrhea accompanied by cramping abdominal pain. During the next days, in most patients watery diarrhea changes to bloody diarrhea. One week after the onset of diarrhea, in about 15% of infected patients under 10 years of age EHEC infection results in a systemic complication, HUS. Shiga toxins (Stxs) are considered the major virulence factors of EHEC involved in the pathogenesis of HUS. It is generally believed that after intestinal infection with EHEC, Stxs cross the intestinal barrier and bind to endothelial cells. At this point they presumably injure the host cell by inhibition of protein synthesis, stimulation of prothrombotic messages, or induction of apoptosis. The B subunit of Stx binds to the membrane receptor globotriaosylceramide (Gb3). Gb3 facilitates the endocytosis and intracellular trafficking of the toxin. The Stx A subunit hydrolyzes a specific adenine residue of the 60S ribosomal subunit of mammalian cells. As a consequence, Stx shuts down the protein machinery of the susceptible cell. The HUS is the net effect of a variety of interacting factors, including background risk of acquisition, host factors (such as age), virulence characteristics of the infecting EHEC strain, and exogenous factors. All known EHEC virulence determinants are located on mobile genetic elements, and this has an important impact on the evolution of these pathogens. The evolution of EHEC has a dynamic component that includes different genetic mechanisms. The recent progress in understanding the pathogenesis and epidemiology of EHEC infections forms a basis for the development of future strategies to prevent EHEC infections in humans.

Rapid and simple method for the detection of shigatoxins (STxs)

Enterohemorrhagic Escherichia coli (EHEC) is an emerged bacterial agent as the cause of bloody diarrhea and a leading cause of hemolytic uremic syndrome in children. In our country, serotype O 157:H7 is the predominant pathogen in the EHEC and the most frequently seen in human infections. The clinical disease is not associated with the STx types produced by the infecting strains. Non-O157 serotypes of EHEC also produce STxs, and infections with some non-O157 EHEC are occasionally associated with the illness caused by O157:H7. A rapid and simple enzyme immunoassay method (EIA) for the detection of STxs was established. This method is based on the use of anti-STx1 or anti-STx2 monoclonal antibody-labelled colloidal gold for detective factor and also used each anti-STx antibody for the capture antibody. The supernatant was used as the test sample after centrifugation of bacterial suspension treated with polymixin B (5,000 u/ml). These EIA-tests were specific for all supernatants of EHEC serotypes used, giving positive reactions (more than 1:16-32) by the RPLA method, and permitted the detection of ca. 203-812 pg of STx1 or STx2 in a 130 microliters applied to this test. This method will be an extremely useful tool for the detection of STxs from isolates or bacteria on selective agar-plates.

Isolation of enterohemorrhagic Escherichia coli O157 strains from patients with hemolytic-uremic syndrome by using immunomagnetic separation, DNA-based methods, and direct culture.

We examined 30 children with classical hemolytic-uremic syndrome (HUS) for the presence of enterohemorrhagic Escherichia coli (EHEC) strains in stool samples and determined the specific immune response to O157 lipopolysaccharide in acute-phase serum samples from these patients. EHEC O157 strains were isolated from stool samples of 18 (60%) of the patients, and non-O157 EHEC strains were isolated from 5 (17%) of the patients. For O157 strain isolation from stools, we introduced a selective enrichment step using O157-specific antibodies attached to paramagnetic particles (immunomagnetic separation [IMS] method). This procedure allowed the detection of O157 strains at 10(2) CFU/g of stool in the presence of 10(7) coliform background flora organisms. By using IMS followed by plating on sorbitol MacConkey (SMAC) agar and cefixime-tellurite SMAC (CT-SMAC) agar, O157 strains were detected in 18 samples, whereas colony hybridization detected a subset of 12 positive samples and direct culture on CT-SMAC or SMAC agar detected only 7. Three of the 18 O157-positive stools were negative by cytotoxicity assay performed with stool filtrates and by direct PCR with DNA extracted from stools. The IMS technique allowed the isolation of O157 strains from 18 of 20 patients with serological evidence for O157 infection. Apart from the increase in sensitivity in O157 detection compared with that of direct culture, the IMS technique also has the advantage of being less labor-intensive and less time-consuming than the molecular methods. IMS can therefore be considered an efficient method for wide-spread use in the detection of O157 strains in clinical microbiology laboratories. However, because a significant number of HUS cases were attributable to non-O157 EHEC serogroups, the use of additional methods besides IMS in the bacteriological diagnosis of HUS is necessary.