Mutual Enhancement of Virulence by Enterotoxigenic and Enteropathogenic Escherichia coli

Abstract

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...

Concomitant EnterotoxigenicEscherichia coliInfection Induces Increased Immune Responses toVibrio choleraeO1 Antigens in Patients with Cholera in Bangladesh

“…The heat-stable toxin (ST) is less well characterized for its immunomodulating properties than are LT and CT. Dual infections of children in developing countries with ETEC and enteropathogenic E. coli (EPEC) have been observed (10,26), and recent studies have shown that purified ST or crude extracts of ETEC can enhance the virulence of EPEC by use of laboratory-based in vitro assay systems (8). This suggested a molecular basis for the role of ST in causing an increased severity of disease in EPEC diarrhea.…”

“…Generally, for toxinmediated enteric infections, robust responses are needed to overcome the effect of the toxins, for achieving protective efficacy for these major pathogens, and to formulate a widerange global vaccine (8). Since the presence of O-blood-group antigen was previously found to be associated with susceptibility to cholera (18) and to be associated with the magnitude of immune responses generated after vaccination (21), we analyzed the effect of this antigen on the immune responses seen for our three study groups.…”

Heat-Labile Enterotoxin PromotesEscherichia coliAdherence to Intestinal Epithelial Cells

“…ATP is subsequently degraded to adenosine, which is able to stimulate a chloride secretory response (8). LT (and STa) had previously been shown to potentiate the release of ATP from EPECinfected cells (7) and may increase disease severity in mixed EPEC/ETEC infections (7).…”

Analysis of Global Transcriptional Profiles of Enterotoxigenic Escherichia coli Isolate E24377A

“…A study by Crane et al identified that the virulence of EPEC prototype strain E2348/69 was enhanced by the release of ATP in the presence of heat-stable toxin (STa) produced by an ETEC isolate (5). Interaction of isolates from these two pathovars has also been previously noted in epidemiological studies (52).…”