Binding of diarrheagenic Escherichia coli to 32- to 33-kilodalton human intestinal brush border proteins

EspC, an autotransporter protein secreted by enteropathogenic Escherichia coli (EPEC), displays protease activity on human hemoglobin

Some enteropathogenic Escherichia coli (EPEC) strains, which are an important cause of diarrhea among infants, secrete a serine protease autotransporter protein called EspC. The pathogenic role of EspC upon EPEC infection is unknown. In this study, we demonstrated that purified EspC protein, obtained from supernatants of EPEC cultures, interacted with hemoglobin and degraded it. Moreover, we have shown that EspC is a hemin-binding protein. We hypothesized that hemoglobin proteolysis by EspC may contribute to the utilization of heme and hemoglobin iron for bacterial growth.

Species-specific cell adhesion of enteropathogenic Escherichia coli is mediated by type IV bundle-forming pili

Enteropathogenic Escherichia coli (EPEC) is a causative agent of diarrhoea in humans. Localized adherence of EPEC onto intestinal mucosa was reproduced in an in vitro adherence assay with cultured human epithelial cells. We found that the efficiency of EPEC adherence to a mouse-derived colonic epithelial cell line, CMT-93, was remarkably lower than its adherence to human-derived intestinal cell lines, such as Intestine-407 or Caco-2. Although EPEC did adhere to some cell lines derived from non-human species, fixing the cells with formalin to inactivate one or more formalin-sensitive factors allowed us to observe species-specific differences in EPEC adherence. In contrast to these results, an EPEC mutant that is defective in bundle-forming pili (BFP) production adhered as efficiently to CMT-93 cells as to Caco-2 cells. Furthermore, Citrobacter rodentium expressing BFP adhered to Caco-2 cells much more efficiently than to CMT-93 cells. Finally, a purified BfpA-His6 fusion protein showed higher affinity for Caco-2 cells than for CMT-93 cells, and inhibited EPEC adherence. Following BFP-mediated adherence, secretion of EspB from adherent bacteria and reorganization of F-actin in the host cells was observed. EPEC adhering to CMT-93 cells induced far less secretion of EspB, or reorganization of F-actin in the host CMT-93 cells, than did EPEC adhering to Caco-2 cells. These results indicated that BFP plays an important role in the cell-type-dependent adherence of EPEC and in the progression to the later steps in EPEC adherence.

Antigen detection in enteropathogenic Escherichia coli using secretory immunoglobulin A antibodies isolated from human breast milk

Enteropathogenic Escherichia coli (EPEC) produces a characteristic attaching and effacing (A/E) lesion in the small intestines of infected children. The immune response to EPEC infection remains poorly characterized. The molecular targets that elicit protective immunity against EPEC disease are unknown. In this study protein antigens from EPEC were identified using secretory immunoglobulin A (sIgA) antibodies isolated from milk from Mexican women by Western blot analysis. Purified sIgA antibodies, which inhibit the adherence of EPEC to cells, reacted to many EPEC proteins, the most prominent of which were intimin (a 94-kDa outer membrane protein) and two unknown proteins with apparent molecular masses of 80 and 70 kDa. A culture supernatant protein of 110 kDa also reacted strongly with the sIgA antibodies. The molecular size of this protein and its reactivity with specific anti-EspC antiserum suggest that it is EPEC-secreted protein C (EspC). These EPEC surface protein antigens were consistently recognized by all the different sIgA samples obtained from 15 women. Screening of clinical isolates of various O serogroups from cases of severe infantile diarrhea revealed that all EPEC strains able to produce the A/E lesion showed expression of intimin and the 80- and 70-kDa proteins. Such proteins reacted strongly with the purified sIgA pool. Moreover, nonvirulent E. coli strains were unable to generate a sIgA response. The immunogenic capacities of the 80- and 70-kDa proteins as virulence antigens have not been previously reported. The strong sIgA response to intimin and the 80- and 70-kDa proteins obtained in this study indicates that such antigens stimulate intestinal immune responses and may elicit protective immunity against EPEC disease.