ADHESIN REGULATORY GENES WITHIN LARGE, UNSTABLE DNA REGIONS OF PATHOGENIC ESCHERICHIA-COLI - CROSS-TALK BETWEEN DIFFERENT ADHESIN GENE CLUSTERS

The uropathogenic Escherichia coil strain 536 possesses two large, uns table DNA regions an its chromosome, which were termed pathogenicity i slands (pais). Deletions of pais, which occur with relatively high fre quency in vitro and in vivo, lead to avirulent mutants. The genetic de terminants for production of haemolysin (Hly) and P-related fimbriae ( Prf) are located in one of these islands. Deletion of this pathogenici ty island (paill) not only removes the hly- and prf-specific genes, bu t also represses S fimbriae (Sfa), although the sfa genes of this viru lence factor are not located on paill. We have identified two regulato ry genes, prfB and prfl, of the prf gene cluster that are homologous t o the sfa regulatory genes sfaB and sfaC, respectively. Mutations in s faB and sfaC that inhibit transcription of the major fimbrial subunit gene sfaA were complemented by the homologous prf genes, suggesting co mmunication between the two fimbrial gene clusters in the wild-type st rain. Chromosomal mutagenesis of the two prf regulators in strain 536 repressed transcription of sfaA, detected by Northern hybridization an d a chromosomal sfaA-lacZ fusion. In addition, haemagglutination assay s measured a lower level of S fimbriae in these mutants. Expression of the cloned prf regulators in trans reversed the effect of the mutatio ns; furthermore, constitutive expression of prfB or prfl could also ov ercome the repression of S fimbriae in a strain that had lost the path ogenicity islands. Virulence assays in mice established that the prf m utants were less virulent than the wild-type strain. The results demon strate that cross-regulation of two unlinked virulence gene clusters t ogether with the co-ordinate loss of large DNA regions significantly i nfluences the virulence of an extraintestinal E. coil wild-type isolat e.