A simple dot immunoassay for detecting antibodies to the lipopolysaccharide of Verocytotoxin-producing Escherichia coli in patients with haemolytic uraemic syndrome

Development of a monoclonal sandwich ELISA for the detection of animal and human Escherichia coli O157 strains

AIMS

Production of a monoclonal antibody (MAb) to Escherichia coli O157 to develop a rapid test using a sandwich ELISA (sELISA) format.

METHODS AND RESULTS

A MAb (7A6) was developed to the long-chain lipopolysaccharide of E. coli O157. A sELISA developed with the MAb reacted with 28 bovine and seven human enterohaemorrhagic E. coli (EHEC) O157 strains and also with two enterotoxigenic E. coli O157 strains. Cross-reaction to a rabbit diarrhoeal E.coli O15, Citrobacter freundii, Salmonella urbana and Vibrio cholerae O1 Inaba was detected.

CONCLUSION

A MAb-based sELISA to detect E. coli O157 was produced. Its application to field samples is required to fully determine its prospective use for the detection of EHEC O157, to evaluate the non-specific interference of the cross-reacting strains.

SIGNIFICANCE AND IMPACT OF THE STUDY

The assay produced is not wholly specific to EHEC O157, but has the potential to be used as a rapid method for screening large numbers of samples for E. coli O157.

The serodiagnosis of infection with Salmonella typhi

BACKGROUND/AIMS

The serodiagnosis of infection with Salmonella typhi, using the Widal agglutination assay, relies on patients' antibodies to the O = 9,12 lipopolysaccharide (LPS) antigens, H = d flagellar antigens, and the Vi capsular antigens. A Vi agglutination titre of > 1/40 has traditionally been regarded as indicative of recent infection with S typhi. In this study, 91 sera were used to assess the reliability of the Widal agglutination assay based on antibodies to the Vi antigens.

METHODS

The Widal agglutination assay was carried out using protocols established by the Central Public Health Laboratory, Colindale. Antibodies to the Vi capsular antigen were detected using a standard preparation of S typhi, ViI Bhatnagar variant strain (S typhi, ViI). Sera used in the study comprised 73 from patients who were culture positive for S typhi, 10 from patients who were culture positive for other species of Salmonella not expressing a Vi antigen (namely, S javiana, S enteritidis, S typhimurium, S stanley, S saint paul, S bareilly, or S mbandaka), and eight from healthy blood donors.

RESULTS

Agglutination titres of > or = 1/40 were detected to S typhi ViI in 69 of 73 sera from patients with typhoid, although 27 of these also agglutinated an unrelated control antigen. The Widal assay also detected significant amounts of agglutinating antibodies to S. typhi ViI in all eight control sera and seven sera from patients infected with S bareilly, S enteritidis, S javiana, S mbandaka, S saint paul, and S stanley.

CONCLUSIONS

Agglutinating antibodies to the Vi antigen can be detected by the Widal assay, but even with the appropriate control antigens the results were unreliable. The serodiagnosis of infections with S typhi should be based on the detection of antibodies to both the O = 9,12 LPS antigen and the H = d flagellar antigen by immunoblotting, and should not use the Vi antigen-based Widal assay. Conclusions should be made in the light of patients' clinical details and any knowledge of previous immunisation for typhoid.

The serodiagnosis of infections caused by Verocytotoxin-producing Escherichia coli

Patients with haemolytic uraemic syndrome (HUS) and haemorrhagic colitis (HC) produce serum antibodies to the lipopolysaccharides (LPS) of Escherichia coli O157 and certain other E. coli serogroups. Patients may also make salivary antibodies to the LPS of E. coli O157. Serological tests based on these antibodies can be used to provide evidence of infection in the absence of culturable VTEC or the toxins they produce. Serum antibodies to LPS persist for several months following onset of disease, enabling both current and retrospective serological testing. The LPS of E. coli O157 shares epitopes with strains of Brucella abortus, Yersinia enterocolitica O9, Vibrio cholerae O1 Inaba, group N Salmonella and certain strains of Citrobacter freundii and E. hermanni. Serological tests for serum antibodies to E. coli O157 should be evaluated in the light of these cross-reactions. Serological tests to supply evidence of infection with E. coli O157 have been shown to provide a valuable adjunct to bacteriological procedures for detecting culturable VTEC and VT. The use of well characterized LPS antigens in association with the techniques of ELISA and immunoblotting provide valuable procedures for detecting evidence of infection with E. coli O157 and possibly other VTEC.

Serodiagnosis of infection with verocytotoxin-producing Escherichia coli

Human sera (167) were screened for antibodies to lipopolysaccharide (LPS) prepared from strains of Verocytotoxin-producing Escherichia coli (VTEC) belonging to a range of serogroups, secreted proteins expressed by attaching and effacing VTEC, enterohaemolysin and H = 7 flagellar proteins. Twelve sera (about 7%) contained antibodies to the LPS of E. coli 05 (one), 026 (two), 0115 (two), 0145 (one), 0163 (one) and 0165 (five). Sera containing antibodies to the LPS of E. coli O26 and O145 also contained antibodies to secreted proteins of 100 and 40 kDa. An additional 34 sera, known to contain antibodies to the lipopolysaccharide of E. coli O157, were examined for antibodies to enterohaemolysin, H = 7 flagellar antigens and bacterial cell surface-associated proteins of 5, 6 and 22 kDa. Three sera contained antibodies to enterohaemolysin and one serum contained antibodies to flagellar proteins. Antibodies to membrane-associated proteins were not detected. It was concluded that enterohaemolysin, H = 7 flagellar proteins and the cell surface-associated proteins were unsuitable for use in immunoassays for providing evidence of infection with VTEC.