ENTEROPATHOGENIC ESCHERICHIA-COLI O103 FROM RABBIT ELICITS ACTIN STRESS FIBERS AND FOCAL ADHESIONS IN HELA EPITHELIAL-CELLS, CYTOPATHIC EFFECTS THAT ARE LINKED TO AN ANALOG OF THE LOCUS OF ENTEROCYTE EFFACEMENT

Escherichia coli O103, a major agent of weaned-rabbit diarrhea in West ern Europe, was previously shown to produce diarrhea and attaching-and -effacing intestinal lesions in experimentally infected rabbits and to possess a homolog of the eaeA gene of enteropathogenic E. coli (EPEC) . In the present study, we have shown that although negative in the fl uorescent-actin staining test on HeLa cells, prototype rabbit E. coli O103 strain B10 was able to induce an original cytopathic effect (CPE) in the same interaction model. This CPE was characterized by a genera lized reorganization of the actin cytoskeleton and the formation of fo cal adhesions on the entire surface of the target cells. These effects amplified with time, leading to cell death about 5 days after the int eraction. They were produced by all rabbit E. coli O103 strains tested , by rabbit-infecting E. coli RDEC-1, and also by two human EPEC isola tes. We localized genes associated with CPE by using TnphoA insertion mutagenesis in strain B10. In all five independent CPE-negative mutant s that we were able to generate, the insertion was located in a region of the genome homologous to the 35-kb locus of enterocyte effacement (LEE locus) of EPEC E2348/69. The mutants concurrently lost the abilit y to secrete four major supernatant proteins of 25, 37, 39, and 40 kDa , which were shown by immunoprecipitation to share antigenic determina nts with secreted proteins of human EPEC E2348/69. The virulence of on e of these mutants (strain B10/CA1) was compared with that of the pare ntal strain in the weaned-rabbit diarrhea model. The mutant was totall y deprived of virulence, although it colonized the intestine as effici ently as the parental strain did. This study points to a new pathogeni c trait of EPEC strains, which is associated with the LEE locus and, p ossibly, with in vivo virulence.