Enterotoxigenic Escherichia coli (ETEC) is a leading cause of infectious diarrhea worldwide. Four categories of antigens have been commonly studied: O serogroup, H serogroup, colonization factor antigens (CFA), and toxins. A database has been complied from published reports of nearly 1,000 ETEC isolates from 18 locations and analyzed to determine the occurrence, distribution, and associations of O serogroup, H serogroup, CFA, and toxin type. Tables listing the associations of antigens are presented. This analysis documents the widespread nature and variety of ETEC. Even the most common combination of antigens, O6:H16 CFA/II LTST, accounted for only 11% of the ETEC isolates in the database. It was isolated from 12 locations. Many phenotypes occurred only once. CFA detection based on enzyme-linked antibodies with polyclonal sera is suggested as the preferred assay. A combination of CFA and toxin-based antigens is suggested as the most practical vaccine.

Transcutaneous immunization (TCI) is a new method for vaccine delivery that has been shown to induce immunity relevant to enteric disease vaccines. We evaluated the clinical safety and immunogenicity of a recombinant subunit vaccine against enterotoxigenic Escherichia coli (ETEC) delivered by TCI. Adult volunteers received patches containing the recombinant ETEC colonization factor CS6, either with heat-labile enterotoxin (LT) or patches containing CS6 alone. The vaccine was administered at 0, 1, and 3 months, and serum antibodies and antibody-secreting cells (ASCs) were assessed. Among the 26 volunteers that completed the trial, there were no responses to CS6 in the absence of LT. In the groups receiving both CS6 and LT, 68 and 53% were found to have serum anti-CS6 immunoglobulin G (IgG) and IgA, respectively; 37 and 42% had IgG and IgA anti-CS6 ASCs. All of the volunteers receiving LT had anti-LT IgG, and 90% had serum anti-LT IgA; 79 and 37% had anti-LT IgG and IgA ASCs. Delayed-type hypersensitivity (DTH), suggesting T-cell responses, was seen in 14 of 19 volunteers receiving LT and CS6; no DTH was seen in subjects receiving CS6 alone. This study demonstrated that protein antigens delivered by a simple patch could induce significant systemic immune responses but only in the presence of an adjuvant such as LT. The data suggest that an ETEC vaccine for travelers delivered by a patch may be a viable approach worthy of further evaluation.

Vibrio anguillarum strain 775 harbouring the virulence plasmid pJM 1 produces a plasmidmediated siderophore that can crossfeed siderophore-deficient, receptor-proficient mutants of V. anguillarum in vitro. Experimental infections of salmonid fishes with mixtures consisting of the wild-type strain and a siderophore-deficient, receptor-proficient mutant resulted in recovery of both the wild-type and the mutant strain, while in infections with mixtures consisting of the wild-type strain and a siderophore-deficient, receptor-deficient mutant only the wild-type strain could be recovered. These results suggest that the V. anguillarum plasmid-mediated siderophore is produced in vivo in a diffusible form and that it is an important factor of virulence.

While Escherichia coli is common as a commensal organism in the distal ileum and colon, the presence of colonization factors (CF) on pathogenic strains of E. coli facilitates attachment of the organism to intestinal receptor molecules in a species- and tissue-specific fashion. After the initial adherence, colonization occurs, and the involvement of additional virulence determinants leads to illness. Enterotoxigenic E. coli (ETEC) is the most extensively studied of the five categories of E. coli that cause diarrheal disease, and has the greatest impact on health worldwide. ETEC can be isolated from domestic animals and humans. The biochemistry, genetics, epidemiology, antigenic characteristics, and cell and receptor binding properties of ETEC have been extensively described. Another major category, enteropathogenic E. coli (EPEC), has virulence mechanisms, primarily effacement and cytoskeletal rearrangement of intestinal brush borders, that are distinct from ETEC. An EPEC CF receptor has been purified and characterized as a sialidated transmembrane glycoprotein complex directly attached to actin, thereby associating CF-binding with host-cell response. Three additional categories of E. coli diarrheal disease, their colonization factors and their host cell receptors, are discussed. It appears that biofilms exist in the intestine in a manner similar to oral bacterial biofilms, and that E. coli is part of these biofilms as both commensals and pathogens.

RDEC-1, an Escherichia coli strain that adheres to rabbit mucosa and causes an attaching, effacing lesion, expresses the pilus adhesin AF/Rl which determines in vitro attachment to rabbit intestinal brush borders. In order to determine the role of AF/Rl pili in the pathogenesis of enteropathogenic diarrhea in rabbits, we localized the genes for AF/Rl expression, constructed an AF/R1strain, and compared the virulence of the AF/ Rl and AF/R1strains with particular attention to the development of attaching, effacing lesions. We introduced TnS into the 86-megadalton (MDa) conjugative plasmid known to mediate expression of AF/Rl pili and transferred the derivative plasmids into laboratory strain HB101. Transconjugant M5 was found to contain the 86-MDa plasmid from RDEC-1 and to express AF/Rl pili. Pilus expression on M5 was confirmed by reaction with antiserum raised against purified AF/Rl pili and allowed the bacteria to adhere to the rabbit ileum in an in vitro assay. Three Tn5 insertions in the 86-MDa plasmid were obtained which resulted in loss of AF/Rl expression. Part of the plasmid was mapped, including a region necessary for AF/Rl pilus expression. AF/R1mutant strain M34 was constructed, and its pathogenesis was investigated. M34 produced disease in rabbits but was less virulent than the parent. The characteristic effacing lesions of RDEC-1 and enteropathogenic E. coli developed in the intestine of rabbits infected with either M34 or RDEC-1, although with M34 they were much less frequent and did not involve the small bowel. We conclude that AF/Rl pilus expression is not essential for the attaching, effacing lesion but serves as an accessory virulence factor which promotes an initial interaction of RDEC-1 with normal epithelial cells. * Corresponding author. .thelial cells (M cells) over the Peyer's patch in the small intestine (13, 14). In their experiments, they used a Shigella flexneri derivative strain, D15, which contained an 85megadalton (MDa) plasmid from RDEC-1 and expressed AF/ Rl pili (10). D15 bacteria were found to adhere specifically to M cells hours after inoculation; however, they did not result in effacing lesions with elongation of microvilli characteristic of RDEC-1 (14). Hence, AF/Ri appears to mediate the attachment of bacteria to M cells early in infection but is not sufficient for attaching, effacing lesions. In the present study, we characterized the 86-MDa plasmid of RDEC-1, constructed mutants in AF/Rl pilus expression, and tested the virulence of an AF/Rl mutant with particular emphasis on its ability to promote attaching, effacing lesions of the absorptive epithelial cells of the ileum, cecum, and colon. MATERIALS AND METHODS Bacterial strains and media. E. coli RDEC-1 is 015:H-:K? and is resistant to nalidixic acid. Strains 640 and HS are commensal strains that were isolated from rabbits and humans, respectively. These were from the collection in the Department of Gastroenterology, Walter Reed Army Institute of Research. HB101 (5) and HU735, the strain containing the Tn5 donor plasmi...