Enterotoxigenic Escherichia coli (ETEC) and enteropathogenic E. coli (EPEC) are common causes of diarrhea in children in developing countries. Dual infections with both pathogens have been noted fairly frequently in studies of diarrhea around the world. In previous laboratory work, we noted that cholera toxin and forskolin markedly potentiated EPEC-induced ATP release from the host cell, and this potentiated release was found to be mediated by the cystic fibrosis transmembrane conductance regulator. In this study, we examined whether the ETEC heat-labile toxin (LT) or the heat-stable toxin (STa, also known as ST) potentiated EPEC-induced ATP release. We found that crude ETEC culture filtrates, as well as purified ETEC toxins, did potentiate EPEC-induced ATP release in cultured T84 cells. Coinfection of T84 cells with live ETEC plus EPEC bacteria also resulted in enhanced ATP release compared to EPEC alone. In Ussing chamber studies of chloride secretion, adenine nucleotides released from the host by EPEC also significantly enhanced the chloride secretory responses that were triggered by crude ETEC filtrates, purified STa, and the peptide hormone guanylin. In addition, adenosine and LT had additive or synergistic effects in inducing vacuole formation in T84 cells. Therefore, ETEC toxins and EPEC-induced damage to the host cell both enhance the virulence of the other type of E. coli. Our in vitro data demonstrate a molecular basis for a microbial interaction, which could result in increased severity of disease in vivo in individuals who are coinfected with ETEC and EPEC. Along with rotavirus, enterotoxigenic Escherichia coli (ETEC)and enteropathogenic E. coli (EPEC) are among the most common causes of diarrhea in children in developing countries (29). Dual infections with both pathogens have been noted fairly frequently in studies of diarrhea around the world for many years (41,42). More recent studies of diarrhea etiology have begun to describe multiple infections carefully, and evidence is emerging that patients with multiple pathogens are likely to experience more-severe diarrheal disease (2,8,24,35,40,59).One might expect dual infections with EPEC and ETEC to occur occasionally by chance alone, especially in povertystricken areas with poor hygiene. However, studies of diarrhea etiology in areas with good sanitation also noted dual infections with EPEC and ETEC. The tendency of EPEC and ETEC to occur in multiple infections has been noted in epidemiology surveys in developed countries such as northern Italy (8), Israel (24), and Yugoslavia prior to the Balkan war (13). EPEC and ETEC coinfection was also found in an investigation of a hospital outbreak in Durban, South Africa (1). Several of the children in the latter outbreak had a triple infection with EPEC, ETEC, and rotavirus.Recent work from our laboratory suggested a molecular mechanism by which EPEC and ETEC might interact. Specifically, we found that cholera toxin (CT) and forskolin enhance EPEC-induced ATP release from the host cell (15) without any enha...

We previously reported that enteropathogenic Escherichia coli (EPEC) infection triggered a large release of ATP from the host cell that was correlated with and dependent on EPEC-induced killing of the host cell. We noted, however, that under some circumstances, EPEC-induced ATP release exceeded that which could be accounted for on the basis of host cell killing. For example, EPEC-induced ATP release was potentiated by noncytotoxic agents that elevate host cell cAMP, such as forskolin and cholera toxin, and by exposure to hypotonic medium. These findings and the performance of the EPEC espF mutant led us to hypothesize that the CFTR plays a role in EPEC-induced ATP release that is independent of cell death. We report the results of experiments using specific, cell-permeable CFTR activators and inhibitors, as well as transfection of the CFTR into non-CFTR-expressing cell lines, which incriminate the CFTR as a second pathway for ATP release from host cells. Increased ATP release via CFTR is not accompanied by an increase in EPEC adherence to transfected cells. The CFTR-dependent ATP release pathway becomes activated endogenously later in EPEC infection, and this activation is mediated, at least in part, by generation of extracellular adenosine from the breakdown of released ATP.