Serological identification of infection by verocytotoxin-producing Escherichia coli

Escherichia coli 'O' group serological responses and clinical correlations in epidemic HUS patients

This first comprehensive serological analysis of an haemolytic uraemic syndrome (HUS) outbreak in which a wide range of 'O' group Escherichia coli antibody responses in patients and controls provided a unique insight into the epidemiology of such epidemics. Possible answers to clinical aspects related to severity of disease and complications were revealed. A microagglutination assay was used to examine E. coli 'O' group serological responses in 49 serum samples of 21 children hospitalised with HUS and 14 single samples from contemporaneous age-matched controls. A total of 51 O serogroup strains were used, including those reported to be associated with cases of HUS, with six isolates from patients associated with the Adelaide outbreak, environmental verocytotoxi-genic/shiga-toxin producing E. coli (VTEC/STEC) strains and common human commensal strains. Amongst the 21 patients, there were 226 instances of seroreactivity (titre > or = 100) against 34 E. coli serogroups while six instances of seroreactivity against four serogroups occurred in controls. There were 128 instances in patients and one instance in controls in which titres > or = 400 were observed. All 21 patients were seroreactive (titre > or = 100 and <400) to one or more of the 17 HUS-associated serogroups included in the study. Titres ranged from 100 to 6,400, some of the highest in three patients were against O157, whose faeces yielded only EHEC O111, and only one developed O111 antibody. Mixed infection was demonstrated serologically by microagglutination (confirmed by western blot) and was consistent with the multiple serogroups of VTEC found in the mettwurst incriminated as the source, and suggests further strains (not found in the source or in patients' faeces) were probably involved. In HUS-associated EHEC infection, multiple strain infection may be the rule rather than the exception. Analysis of 34 of the 51 serogroup antibody responses in the HUS patients revealed clues to possible relationships with clinical severity and complications. Patients with severe renal failure tended to develop antibodies to a larger number of serogroups than those with moderate or mild impairment. The same was true for central nervous system complications. Other associations were observed. While VTEC O157 remains an important causal serogroup in HUS, non-O157 serogroups also appear to play a significant role and therefore the latter should always be sought in all future HUS cases as new insights into pathogenicity may be discovered. This study indicates that co-infection with different VTEC serogroups may affect clinical outcome.

Heterogeneity of environmental, retail, and clinical isolates of Vibrio vulnificus as determined by lipopolysaccharide-specific monoclonal antibodies

The opportunistic pathogen Vibrio vulnificus expresses lipopolysaccharide (LPS) antigens on its outer membrane surface. A serological typing system was developed for these antigens, utilizing the discriminatory recognition of monoclonal antibodies (MAb) by ELISA. MAb were used to recognize five unique types of LPS-associated antigens for examination of clinical. environmental, and retail isolates of V. vulnificus. The overall serotype profile of the clinical isolates was significantly different (P < 0.05) from that of the environmental and retail isolates. A higher percentage of clinical isolates were typable (61%) compared to the environmental isolates (41%) and retail isolates (44%). In particular, the percentage of serotype 1/5 among clinical isolates (33%), compared to that of environmental (9%) and retail (4%), was highly significant (P < 0.0001). Among the environmental Gulf Coast isolates, there were differences in the prevalence of serotypes 2 and 3 (P < 0.05), depending on whether isolates were obtained from Louisiana or Alabama harvest sites. There were no statistically significant differences between the serotype profiles of Gulf and Atlantic Coast retail isolates despite the absence of serotype 1/5 from the Atlantic Coast. While some serotype diversity was detected in V. vulnificus isolated during different seasons, from different geographic locations, and at retail versus at harvest, there was no apparent concordance between any of the serotype distributions obtained from oysters versus that isolated clinically. The heterogeneity of environmental isolates and relative homogeneity among clinical isolates suggest that human risk may not be predicted on quantitative exposure alone.

Antibodies to lipopolysaccharides of Escherichia coli serogroups O5 and O165 in healthy adults

The observation that over 50% of healthy blood donors have serum antibodies to the lipopolysaccharide of Escherichia coli O5 and O165 influences the serodiagnosis of infection with verocytotoxin-producing E. coli.

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.