Distribution of the Escherichia coli Common Pilus among Diverse Strains of Human Enterotoxigenic E. coli

The Escherichia coli common pilus (ECP) is produced by commensal and pathogenic E. coli strains. This pilus is unrelated to any of the known colonization factors (CFs) of enterotoxigenic E. coli (ETEC). In this study, we investigated the distribution and production of ECP among a collection of 136 human CF-positive and CF-negative ETEC strains of different geographic origins. The major pilus subunit gene, ecpA, was found in 109 (80%) of these strains, suggesting that it is widely distributed among ETEC strains. Phenotypic analysis of a subset of 43 strains chosen randomly showed that 58% of them produced ECP independently of the presence or absence of CFs, a percentage even higher than that of the most prevalent CFs. These data suggest an important role for ECP in the biology of ETEC, particularly in CF-negative strains, and in human infection.Enterotoxigenic Escherichia coli (ETEC) is an important cause of diarrheal disease and mortality for children living in developing countries (11). The presence of ETEC in these areas is associated with a lack of sanitation or poor sanitation and the consumption of contaminated water or food. The main virulence factors of ETEC are a heat-labile (LT) and/or a heat-stable (ST) enterotoxin and multiple adhesive pili called colonization factors (CFs) (1, 7), which are produced in the small intestine and can cause life-threatening, cholera-like watery diarrhea (7). Since the early 1970s, more than 25 different CFs have been reported in ETEC strains of diverse geographic origins, and the prevalence of these pili differs by geographic region (7, 11). Studies of the prevalence and distribution of CFs among ETEC strains worldwide have shown that the most common CFs are CFA/I and combinations of E. coli surface antigens CS1, CS2, and CS3 or of antigens CS4, CS5, and CS6. Approximately 50% of ETEC strains contain at least one of these CFs (7), leaving 50% of strains that do not produce any of the CFs known or characterized so far. The presence of type IV pili, which are associated with host colonization and virulence in many gram-negative bacteria, has also been demonstrated in a significant number (30 to 50%, depending on the geographic source) of ETEC strains, including strains that do not harbor any of the known CFs. These pili provide a mechanism for the organisms to colonize the human gut and establish gastrointestinal disease. Epidemiological studies have shown that protective immunity, attributed to the antigenic variety of the CFs produced, can be achieved through multiple infections. Thus, it is believed that vaccines aimed at preventing ETEC infections, particularly in the young population and travelers, should contain the immunogenic B subunit of the LT and a combination of the most common CFs (7, 9, 10).Previously, it was reported that meningitis-associated E. coli strains, and not other E. coli pathogroups, were able to assemble a “meningitis-associated temperature-dependent pilus” (Mat) after growth at 20°C in Luria-Bertani (LB) medium. The major pilus subunit of the Mat pilus is encoded by the yagZ gene, commonly found in all E. coli strains. Recently, our laboratory reported that most (75%) strains of human and animal E. coli pathogroups (including ETEC), as well as commensal E. coli strains, produce at 37°C a pilus adhesive structure composed of a major 21-kDa protein pilin subunit corresponding to the product of the yagZ gene (8). Because this gene was demonstrated to be widely distributed and highly conserved among E. coli strains, and because production of the pili was shown in the major E. coli pathovars, it was proposed that the pilus be renamed “E. coli common pilus,” or ECP, and that the gene encoding the pilin subunit be designated ecpA. A role for ECP in adherence to cultured human epithelial cells was demonstrated in enterohemorrhagic E. coli (EHEC) O157:H7 and commensal E. coli strains (8).ECP is not related to any of the known ETEC CFs. The present study was carried out to further investigate the presence of ecpA and to determine the production of ECP in a collection of human ETEC strains that had previously been characterized as CF positive or CF negative. We found ECP production in both groups of strains at rates comparable to those found for the most common CFs. Our data suggest that the production of ECP in ETEC strains may contribute to the adhesive properties of this organism and may represent a target for vaccine development and the prevention of ETEC infections.