title: Characterization of the plasmid from Escherichia coli RDEC-1 that mediates expression of adhesin AF/R1 and evidence that AF/R1 pili promote but are not essential for enteropathogenic disease.
abstract: RDEC-1, an Escherichia coli strain that adheres to rabbit mucosa and causes an attaching, effacing lesion, expresses the pilus adhesin AF/R1 which determines in vitro attachment to rabbit intestinal brush borders. In order to determine the role of AF/R1 pili in the pathogenesis of enteropathogenic diarrhea in rabbits, we localized the genes for AF/R1 expression, constructed an AF/R1- strain, and compared the virulence of the AF/R1+ and AF/R1- strains with particular attention to the development of attaching, effacing lesions. We introduced Tn5 into the 86-megadalton (MDa) conjugative plasmid known to mediate expression of AF/R1 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/R1 pili. Pilus expression on M5 was confirmed by reaction with antiserum raised against purified AF/R1 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/R1 expression. Part of the plasmid was mapped, including a region necessary for AF/R1 pilus expression. AF/R1- mutant 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/R1 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.
mesh_terms: D018830:Adhesins, Escherichia coli; D000818:Animals; D000942:Antigens, Bacterial / Q000032:analysis; D001422:Bacterial Adhesion; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics*; D002432:Cecum / Q000382:microbiology; D002874:Chromosome Mapping; D003106:Colon / Q000382:microbiology; D004252:DNA Mutational Analysis; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics / Q000472:pathogenicity*; D010861:Fimbriae, Bacterial / Q000502:physiology*; D005798:Genes, Bacterial; D007082:Ileum / Q000382:microbiology; D007413:Intestinal Mucosa / Q000382:microbiology; D008854:Microscopy, Electron; D008871:Microvilli / Q000382:microbiology; D010957:Plasmids; D011817:Rabbits
chemical_list: D018830:Adhesins, Escherichia coli; D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D004251:DNA Transposable Elements; D004269:DNA, Bacterial