ABSTRACT
An Escherichia coli K-12 transformant carrying 96.5-kb plasmid pLV501 from enteropathogenic E. coli (EPEC) strain K798 is able to produce the same characteristic attaching-effacing lesions in a rabbit ileal biopsy explant model as its parent strain. Cloned EcoRI-SalI DNA restriction fragments from this plasmid failed to reproduce the attaching-effacing lesions, but one recombinant plasmid, pLV527, containing 4.5 kb of pLV501 DNA, conferred on E. coli DH1 transformants the ability to invade enterocytes in the rabbit explant model. DH1(pLV527) was also able to adhere to and invade HEp-2 cells. The relative invasive ability of DH1(pLV527) was quantified by recovery of internalized bacteria following gentamicin treatment of infected HEp-2 monolayers. DH1(pLV527) was 1,000-fold more invasive than DH1 carrying pBR322 or a recombinant plasmid which had no physiological effect on ileal biopsy explants but was less invasive than an enteroinvasive E. coli strain or a transformant carrying the cloned invasion genes of Shigella flexneri. Invasion by DH1(pLV501) could also be detected but occurred at a level 30 times lower than that by DH1(pLV527). Colony-hybridization of the pLV527 insert against a panel of 49 EPEC and related strains revealed that only 11 contained pLV527-hybridizing sequences; thus, the invasion determinant is not an essential component of the attachment-effacement pathogenic mechanism. One pLV527-hybridizing strain displayed both attachment-effacement and invasiveness in the rabbit ileal biopsy explant model. No significant hybridization was observed to non-EPEC invasive pathogenic enteric bacteria, indicating that the invasion determinant encoded on pLV527 is distinct from those used by these organisms.
