Most Escherichia coli strains live harmlessly in the intestines and rarely cause disease in healthy individuals. Nonetheless, a number of pathogenic strains can cause diarrhea or extraintestinal diseases both in healthy and immunocompromised individuals. Diarrheal illnesses are a severe public health problem and a major cause of morbidity and mortality in infants and young children, especially in developing countries. E. coli strains that cause diarrhea have evolved by acquiring, through horizontal gene transfer, a particular set of characteristics that have successfully persisted in the host. According to the group of virulence determinants acquired, specific combinations were formed determining the currently known E. coli pathotypes, which are collectively known as diarrheagenic E. coli. In this review, we have gathered information on current definitions, serotypes, lineages, virulence mechanisms, epidemiology, and diagnosis of the major diarrheagenic E. coli pathotypes.

We showed that Escherichia coli strains attach to HeLa cells in two different patterns. In one, the bacteria cover the whole surface of the cell (diffuse adherence), and in the other, attachment is limited to one or a few sites of the cell surface (localized adherence). Among the enteropathogenic strains, serogroups 055, 086, Olilab, 0119, 0125, 0128ab, and 0142 usually showed localized adherence when tested in the presence of Dmannose. Localized adherence was not shown either by E. coli strains isolated from urine or by enteroinvasive and enterotoxigenic E. coli strains. Some of these strains showed diffuse adherence. Some strains of serogroups 055, 0111, and 0119 showed both localized and diffuse adherence in the same preparation. Mannose-resistant adherence was not related to colonization factor antigens.

The mechanisms by which bacteria resist cell-mediated immune responses to cause chronic infections are largely unknown. We report the identification of a large gene present in enteropathogenic strains of Escherichia coli (EPEC) that encodes a toxin that specifically inhibits lymphocyte proliferation and interleukin-2 (IL-2), IL-4, and gamma interferon production in response to a variety of stimuli. Lymphostatin, the product of this gene, is predicted to be 366 kDa and shares significant homology with the catalytic domains of the large clostridial cytotoxins. A mutant EPEC strain that has a disruption in this gene lacks the ability to inhibit lymphokine production and lymphocyte proliferation. Enterohemorrhagic E. coli strains of serotype O157:H7 possess a similar gene located on a large plasmid. Loss of the plasmid is associated with loss of the ability to inhibit IL-2 expression while transfer of the plasmid to a nonpathogenic strain of E. coli is associated with gain of this activity. Among 89 strains of E. coli and related bacteria tested, lifA sequences were detected exclusively in strains capable of attaching and effacing activity. Lymphostatin represents a new class of large bacterial toxins that blocks lymphocyte activation.Bacteria have evolved a number of mechanisms, including antiphagocytic factors, leukotoxins, and systems for iron chelation, to resist the nonspecific (innate) immune response of vertebrate hosts (25). In addition, several mechanisms to circumvent humoral immunity have been described, such as immunoglobulin A proteases and immunoglobulin-binding proteins. However, few bacterial factors that specifically interfere with cellular immune responses have been described (69). In addition, the mechanisms that allow certain bacterial pathogens to colonize hosts for prolonged periods remain obscure.Enteropathogenic Escherichia coli (EPEC) is a leading cause of diarrhea among infants in developing countries. EPEC is one of the few known bacterial causes of chronic diarrhea (24,34,55). EPEC strains are characterized by their ability to induce profound cytoskeletal rearrangements in host cells that result in the formation of adhesion pedestals upon which the bacteria rest (47). This phenomenon is known as the attaching and effacing effect. Enterohemorrhagic E. coli (EHEC) strains, a subgroup of Shiga-toxin-producing E. coli, also have attaching and effacing activity (26, 64). We previously reported that EPEC produce and secrete a high-molecular-weight, proteasesensitive factor that selectively inhibits production of interleukin-2 (IL-2), IL-4, IL-5, and gamma interferon by human peripheral and lamina propria mononuclear cells and inhibits proliferation of these cells (35,36,41). This inhibitory effect was observed regardless of whether the cells were stimulated by phorbol esters, mitogens, CD3 cross-linking, or antigen. The effect was also seen in macrophage-depleted T-cell populations and in Jurkat cells, indicating that this activity did not require participation of cells other than lymphocytes. ...

We have developed two multiplex PCR assays that detect typical and atypical enteropathogenic Escherichia coli (EPEC) isolates, enteroaggregative E. coli (EAEC) isolates, enterotoxigenic E. coli (ETEC) isolates, enteroinvasive E. coli (EIEC) isolates, Shiga toxin-producing E. coli (STEC) isolates, and Shigella spp. The targets selected for each group were eae and bfpA for EPEC isolates, the target of probe CVD432 for EAEC isolates, the genes encoding heat-labile and heat-stable toxins for ETEC isolates, stx 1 and stx 2 for STEC isolates, and ipaH for EIEC isolates and Shigella spp. These PCRs were specific and sensitive for rapid detection of target isolates in stools. Among 150 stool specimens from the acute diarrhea tested, 9 samples (6%) had atypical EPEC, 9 (6%) had typical EPEC, 7 (4.7%) had EAEC, 3 (2%) had EIEC, 3 (2%) had Shigella spp., and 1 (0.7%) had an O26 STEC strain; we also detected mixed infections, 2 (1.3%) with EAEC and Shigella spp., 1 (0.7%) with atypical and typical EPEC strains, and another with atypical EPEC and EAEC strains. One of the multiplex PCRs directly applied to 36 stool specimens correctly identified 100% of EPEC and EAEC isolates.Five categories of Escherichia coli have been well associated with diarrhea in several epidemiological studies (9)and Shiga toxin-producing E. coli (STEC). The virulence mechanisms that characterize these categories of E. coli are genetically encoded by chromosomal, plasmid, and bacteriophage DNAs and are represented by the following genes: eae (attaching and effacing lesions), bfpA (localized adherence), the gene encoding enteroaggregative adherence, ipaH (enteroinvasive mechanism), the genes encoding heat-labile toxin (LT) and heat-stable toxin (ST), and stx 1 and stx 2 (Shiga toxins). To correctly identify diarrheagenic E. coli strains, these organisms must be differentiated from nonpathogenic members of the normal flora. Serotypic markers correlate, sometimes very closely, with specific categories of diarrheagenic E. coli; however, these markers are rarely sufficient in and of themselves to reliably identify a strain as diarrheagenic. Thus, the detection of diarrheagenic E. coli has focused increasingly on the identification of certain characteristics which themselves determine the virulence of these organisms. This identification process may include HEp-2 cell adherence, DNA hybridization, and PCR assays to detect the presence of specific virulence traits or the genes encoding these traits. The first two types of assays require special expertise, employ cell culture and radioactive material, and are time-consuming.We developed two multiplex PCR assays to detect the five categories of diarrheagenic E. coli organisms and Shigella spp.and assessed the direct application of those assays to human diarrheal stool samples.The targets selected for each category were eae and bfpA for EPEC isolates, the target of probe CVD432 for EAEC isolates, the LT and ST genes for ETEC isolates, stx 1 and stx 2 for STEC isolates, and ipaH for EIEC isolates and Shigella sp...

The virulence profiles of most atypical enteropathogenic Escherichia coli (EPEC) strains are unknown. A total of 118 typical and atypical strains of EPEC serotypes and non-EPEC serogroups isolated from children with or without acute diarrhea who were from different cities in Brazil were examined for virulence-associated markers and adherence to HEp-2 cells, and also had random amplified polymorphic DNA (RAPD) analysis performed. Atypical strains were identical to typical strains with regard to the virulence factors encoded on the locus of enterocyte effacement (LEE). In contrast with typical EPEC strains, none of the atypical strains reacted with the bfpA probe, and half of the strains hybridized with the perA probe. Most atypical strains presented Tir sequences that correlated with enteropathogenic or enterohemorrhagic E. coli (98%), had LEE inserted in either selC or pheU (88%), and presented a typeable intimin (52%). Eighteen new serotypes were found in the EPEC strains. Atypical and typical EPEC strains belonged to different RAPD clusters. Most atypical strains showed a localized-like adherence pattern (61.5%). Of the non-LEE-encoded virulence factors, enteroaggregative E. coli heat-stable enterotoxin was noted most frequently (45%) and was significantly associated with diarrhea (P=.01). Thus, this virulence marker may be used as an additional tool for the diagnosis of truly atypical pathogenic strains.