Human Response to Escherichia coli O157:H7 Infection: Antibodies to Secreted Virulence Factors

Abstract

Vaccination has been proposed for the prevention of disease due to enterohemorrhagic Escherichia coli (EHEC), but the immune response following human infection, including the choice of potential antigens, has not been well characterized. To study this, sera were obtained from five pediatric patients with acute diarrhea caused by E. coli O157:H7 0, 8, and 60 days after hospitalization. These sera were used to examine the immune response to four different EHEC virulence factors: Tir (translocated intimin receptor, which is inserted into the host cell membrane), intimin (bacterial outer membrane protein which binds to Tir), EspA (secreted protein which forms filamentous structures on EHEC surface), and EspB (inserted into the host membrane and cytoplasm). The response to O157:H7 lipopolysaccharide was also examined. Sera were assayed against purified recombinant proteins using immunoblot analysis and by enzyme-linked immunosorbent assay to determine the sera's titers to each of the antigens in all patients. We found that there was little reaction to EspA, EspB, and intimin in the acute-phase sera, although there was some reactivity to Tir. By day 8, titers of antibody to all four virulence factors were present in all patients, with a very strong response against Tir (up to a titer of 1:256,000), especially in hemolytic-uremic syndrome patients, and lesser strong responses to the other three antigens. The titer to the antigens 60 days after hospitalization was decreased but was still highest for Tir. These results suggest that there is a strong immune response to Tir, and to a lesser extent to the other three virulence factors, following EHEC disease, indicating that these bacterial molecules are potential vaccine candidates for preventing EHEC disease. They also suggest that bacterial virulence factors that are inserted into host cells during infection by type III secretion systems (Tir or EspB) are still recognized by the host immune response.Enterohemorrhagic Escherichia coli (EHEC) (also called verotoxigenic E. coli) is an important cause of diarrhea. This organism also produces a toxin which plays a role in disease (verotoxin or Shiga-like toxin [SLT]). Most patients with EHEC infection recover uneventfully within a few days, but in about 8% of cases (23) the diarrhea is followed by hemolyticuremic syndrome (HUS), a life-threatening complication with a substantial morbidity in survivors (19,25). HUS appears to be caused by the interaction of SLT with endothelial cells. Worldwide, many serotypes of EHEC have been described, but in North America one type predominates, E. coli O157:H7 (11, 12). Epidemiological evidence shows that EHEC O157:H7 strains are present in the feces of healthy cattle, providing indirect evidence that EHEC O157:H7 can colonize the bovine intestine without causing disease.Because of the potential seriousness of EHEC infection (4), vaccination has been proposed, either to prevent the disease in humans or to reduce colonization in cattle. However, the immunological response to EHEC infection ...

Memory AND effector cells in children with bacterial infections of the gastrointestinal and respiratory tracts

“…Indeed, a number of papers have evaluated the immunological response against specific bacterial agents, such as E. coli and Coxiella burnetii [14,15]. In the current study, we detected E. coli in a number of patients with gastrointestinal infections, and Staphylococcus aureus and Klebsiella were found in patients with respiratory infections.…”

Vaccines for viral and bacterial pathogens causing acute gastroenteritis: Part II: Vaccines forShigella,Salmonella,enterotoxigenicE. coli(ETEC) enterohemorragicE. coli(EHEC) andCampylobacter jejuni

“…The characterization of STEC antigens using human serum, naturally and artificially infected cattle and other animal models, has allowed the identification of different immunogenic proteins that have been proposed as targets for the development of vaccines. [130][131][132][133][134][135] The antigens best characterized immunologically, and that have been used systematically in different vaccine candidates, include: the Shiga toxins Stx1 and Stx2, LPS, flagellin (FliC -H7) and virulence factors encoded in the LEE and secreted by a TTSS, such as Tir, intimin, EspA, EspB and EspD. The use of effectors coded by the LEE has been particularly attractive, given their importance in STEC pathogenesis and due to the possibility of generating cross-protection against enteropathogenic Escherichia coli (EPEC) [reviewed in 136 ]; this is another important pathotype associated with infantile diarrhea that presents an LEE locus with a high degree of homology.…”

OMV-based vaccine formulations against Shiga toxin producingEscherichia colistrains are both protective in mice and immunogenic in calves

“…Moreover, the sera from HUS patients and infected cattle cross-recognize most of the virulence factors known to have a critical role in colonization. 44–46 Although our work is focused on preventing infection in cattle, it could be expected that an effective vaccine candidate against infection in cattle could also be effective against infection in humans, a critical aspect for the control of outbreaks. Studying the inhibition of bacterial adhesion to cell lines or tissue explants by sera from immunized animals could add complementary information to the functional analysis of immunized sera.…”