EPITHELIAL-CELL INVASION BY BOVINE SEPTICEMIC ESCHERICHIA-COLI

Little is known regarding the pathogenesis of Escherichia coli-induced septicemic colibacillosis of calves. To understand the mechanism by w hich these strains penetrate the intestinal epithelium and gain access to the bloodstream, we examined the potential of bovine septicemic E. coil to invade cultured epithelial cells. By using a gentamicin survi val assay, we demonstrated bacterial invasion of Madin-Darby canine ki dney (MDCK) cells. Transcytosis of polarized MDCK cell monolayers was also observed, but only when bacteria were added to the basolateral su rface. Electron microscopy confirmed the presence of intracellular org anisms which appeared to be within membrane-bound vacuoles. The bovine septicemic isolate used in this study expressed the fimbrial adhesin CS31A. To examine the role of CS31A-mediated adherence in invasion and transcytosis of MDCK cell monolayers, a CS31A-deficient mutant was co nstructed by suicide vector-mediated insertional mutagenesis. Although nonadherent, the mutant showed a level of invasion similar to that of the wild-type parent. E. coli DH5 alpha carrying the cloned CS31A det erminant was noninvasive. These findings suggest that expression of CS 31A is neither required nor sufficient to mediate invasion.