CLONAL RELATIONSHIPS AMONG BLOOD-STREAM ISOLATES OF ESCHERICHIA-COLI

The clonal relationships among 187 bloodstream isolates of Escherichia coli from 179 patients at Boston, Mass., Long Beach, Calif., and Nair obi, Kenya, were determined by multilocus enzyme electrophoresis (MLEE ), analysis of polymorphisms associated with the ribosomal operon (rib otyping), and serotyping. MLEE based on 20 enzymes resolved 101 electr ophoretic types (ETs), forming five clusters; ribotyping resolved 56 d istinct patterns concordant with the analysis by MLEE. The isolates at each study site formed a genetically diverse group and demonstrated s imilar clonal structures, with the same small subset of lineages accou nting for the majority of isolates at each site. Moreover, two ribotyp es accounted for similar to 30% of the isolates at each study site. On e cluster contained the majority (65%) of isolates and, by direct comp arison of the ETs and ribotypes of individual isolates, was geneticall y indistinguishable from the largest cluster for each of two other col lections of E. coli causing pyelonephritis and neonatal meningitis (R. K. Selander, T. K. Korhonen, V. Vaisanen-Rhen, P. H. Williams, P. E. Pattison, and D. A. Caugent, Infect. Immun. 52:213-222, 1986; M. Arthu r, C. E. Johnson, R. H. Rubin, R. D. Arbeit, C. Campanelli, C. Kim, S. Steinbach, M. Agarwal, R. Wilkinson, and R. Goldstein, Infect. Immun. 57:303-313, 1989), thus defining a virulent set of lineages. The isol ates within these virulent lineages typically carried DNA homologous t o the adhesin operon pap or sfa and the hemolysin. operon hly and expr essed O1, O2, O4, O6, O18, O25, or O75 antigens. DNA homologous to pap was distributed among isolates of each major cluster, whereas hly was restricted to isolates of two clusters, typically detected in pap-pos itive strains, and sfa was restricted to isolates of one cluster, typi cally detected in pap- and hly-positive strains. The occurrence of pap -positive isolates in the same geographically and genetically divergen t lineages suggests that this operon was acquired early in the radiati on of E. coli, while hly and sfa were acquired subsequently, most like ly by pap-positive and pap- and hly-positive precursors, respectively.