Molecular analysis of the virulence determinants of enterotoxigenic Escherichia coli isolated from domestic animals: applications for vaccine development

Chromosomal integration and expression of the Escherichia coli K88 gene cluster in Salmonella enterica ser. Choleraesuis strain 54 (SC54)

Attempts to develop live vaccines to protect against enterotoxigenic Escherichia coli (ETEC) infection by induction of both cell-mediated and mucosal immunity, and serum antibody responses have included use of recombinant Salmonella strains that produce K88 fimbrial antigens (Hone et al., 1988; Attridge et al., 1988; Morona et al., 1994). However, none of the recombinant Salmonella vectors has been licensed by the United States Department of Agriculture (USDA) for use as a live vaccine in pigs in the United States. A variant of Salmonella enterica ser. Choleraesuis strain 54 (SC54) is currently used as a safe and effective intranasal attenuated live vaccine in pigs. In order to expand the efficacy of this live vaccine strain, we sought to modify strain SC54 to express the K88 antigens of ETEC. To accomplish this, a plasmid-based system was used to integrate the K88 gene cluster into the chromosome of strain SC54 by site-specific recombination. The K88 antigens were expressed by strain SC54, and the gene cluster was stably maintained in the host.

Swine and cattle enterotoxigenic Escherichia coli-mediated diarrhea. Development of therapies based on inhibition of bacteria-host interactions

Enterotoxigenic Escherichia coli (ETEC) frequently occurs in diarrheal disease afflicting domestic animals. In this paper is summarized the research carried out over the last decade on the two important determinants of virulence that plays a role in the development of the infection, namely the colonizing ability of the small intestine mediated by specific fimbrial adhesins acting as lectins and the production of enterotoxins. Recent progress in knowledge of the phenomenon led to alternative strategies of prevention and cure of enteric infection. Since bacterial recognition of mucosa surface receptors in an initial event in colonization, several approaches based on the competitive inhibition of ETEC adhesion have been developed. This review examines the following approaches: competitive colonization with non pathogenic strains, design of adhesin or toxin vaccines, receptor analog therapy and methods for in vivo suppression of virulence factors.

Some infectious causes of diarrhea in young farm animals

Escherichia coli, rotaviruses, and Cryptosporidium parvum are discussed in this review as they relate to enteric disease in calves, lambs, and pigs. These microorganisms are frequently incriminated as causative agents in diarrheas among neonatal food animals, and in some cases different strains or serotypes of the same organism cause diarrhea in humans. E. coli causes diarrhea by mechanisms that include production of heat-labile or heat-stable enterotoxins and synthesis of potent cytotoxins, and some strains cause diarrhea by yet undetermined mechanisms. Rotaviruses and C. parvum induce various degrees of villous atrophy. Rotaviruses infect and replicate within the cytoplasm of enterocytes, whereas C. parvum resides in an intracellular, extracytoplasmic location. E. coli, rotavirus, and C. parvum infections are of concern to producers, veterinarians, and public health officials. These agents are a major cause of economic loss to the producer because of costs associated with therapy, reduced performance, and high morbidity and mortality rates. Moreover, diarrheic animals may harbor, incubate, and act as a source to healthy animals and humans of some of these agents.

Glycoprotein glycans that inhibit adhesion of Escherichia coli mediated by K99 fimbriae: treatment of experimental colibacillosis

Calf diarrhea due to infection by enterotoxigenic Escherichia coli was treated by administration of glycoprotein glycans derived from bovine plasma. The glycan moieties of the nonimmunoglobulin fraction of plasma mimicked the oligosaccharide moiety of intestinal receptors recognized by K99 pili. These glycoprotein glycans inhibited adhesion of E. coli K99+ ST+ to erythrocyte glycoconjugates in vitro, and they protected colostrum-deprived newborn calves against lethal doses of enterotoxigenic E. coli (10(10) bacteria). Adhesion of bacteria to the intestines (duodenum, jejunum, and ileum) was significantly reduced (by 2 orders of magnitude) in treated calves.

In vivo properties of a cloned K88 adherence antigen determinant

An Escherichia coli strain of serotype O9:K36:H19 harboring the K88 recombinant plasmid pMK005 was able to efficiently colonize the small bowel of young piglets after oral infection. The strain expressed K88 antigen in vivo, and bacteria were detected in close association with the surface of the intestinal villi. Mice infected orally or intravenously with attenuated Salmonella typhimurium SL3261 harboring pMK005 were well protected against subsequent challenge with the highly virulent S. typhimurium SL1344. Anti-K88 antibodies were detected in the serum of mice immunized with SL3261(pMK005).

Expression of a cloned 987P adhesion-antigen fimbrial determinant in Escherichia coli K-12 strain HB101

The properties of three independent enterotoxigenic Escherichia coli isolates known to express 987P adhesion fimbriae in a manner subject to phase variation were examined. Phase variation could not be correlated with any major changes in the plasmid DNA content of these strains or with readily detectable changes in any other tested phenotypic markers. The 987P genetic determinant from one of these strains, E. coli 987, was cloned into the non-fimbriated E. coli K-12 strains HB101, and expressed, using the cosmid vector system. 987P fimbriae produced by cells harbouring these recombinant plasmids (987P+ phenotype) could not be distinguished from 987P fimbriae produced by strain 987. Expression of 987P fimbriae from some recombinant plasmids was unstable but none of the recombinants exhibited the phase variation phenotype displayed by the parental strain. One recombinant plasmid, pPM200, contained an insert of strain 987 DNA of ca. 33 kb. The HB101[pPM200] displayed a rather stable 987P+ phenotype, but this was not true for several hosts, since pPM200 acquired approx. 20-kb deletions following transformations of E. coli K-12 strains other than HB101. The deletions mapped to the same region of pPM200 irrespective of the host strain transformed. Cells harbouring the deleted plasmids did not express 987P fimbriae (987P- phenotype).