Phenotypic and genotypic assays for the detection and identification of adhesins from pyelonephritic Escherichia coli

Four different gene clusters have been characterized so far which encode adhesins involved in the specific binding of pathogenic Escherichia coli to epithelial cells of the urinary tractus: the pap, sfa, afa and bma operons. The ability to adhere to uroepithelial cells and to interact with one or several of the specific receptors identified for each of the 4 adhesins, has been studied for 102 E. coli strains isolated from patients with pyelonephritis. These receptor-binding assays are referred to as phenotypic assays. Isolates which adhered to uroepithelial cells 68.6% produced at least 1 of the previously described adhesins. In addition, we used DNA probes to detect homologous sequences of the pap, sfa, and afa operons. Genotypic assays revealed that 87.2% of pyelonephretic E. coli contain DNA sequences related to at least 1 of the 4 operons; 78.4%, 22.5% and 11.8% of the strains harboured sequences related to pap, sfa and afa operons, respectively. The afa- and sfa-adhesion determinants were commonly found associated with the presence of the pap operon (8.8% and 18.6%, respectively). Detection of adhesins using the genotypic approach appears to be reliable (all adhesins detected using the phenotypic approach were also detected with probes). Detection by colony hybridization was significantly higher than by phenotypic assay. Discrepancies may have been due to absence of expression of the detected operons and may have resulted from improper in vitro growth conditions, phase variation, and/or heterogeneity of the genes encoding the adhesins within a family of related sequences.