Among the adhesin-encoding virulence operons associated with uropathogenic Escherichia coli, only pap (pyelonephritis-associated pilus)-related gene clusters typically exhibit variation in their structure and chromosomal copy number. To access further such variability, we compared pap restriction fragment length polymorphisms (RFLPs) with those detected among rRNA (rrn) operons, which encode an essential host function unrelated to virulence. To place such findings in a phylogenetic perspective, the E. coli isolates were also characterized by using multilocus enzyme electrophoresis. Variation in the rrn RFLP profiles correlated with evolutionary divergence resolved by multilocus enzyme electrophoresis; isolates with identical rrn profiles represented the same or closely related electrophoretic types. In contrast, such isolates frequently had different pap-related RFLPs, indicating that these genetic variations have developed recently relative to the changes associated with essential rrn operons or metabolic enzymes. Despite such fluctuations, two lines of evidence indicate conditions under which the pap-related RFLPs can be stably maintained. First, for each of 20 patients with urosepsis, both the primary urinary tract isolate and the concurrent blood isolate were identical. Second, although obtained from different patients, some isolates representing the same electrophoretic type also had identical pap-related RFLPs. Thus, the genotypic diversity of this virulence adhesin operon was not generated during the course of acute infection or during laboratory manipulations. Since fecal E. coli isolates frequently carry chromosomally encoded pap-related gene clusters, these findings suggest that the intraand interchromosomal recombination events generating the polymorphisms associated with the pap-related sequences likely occur among the E. coli of the commensal reservoir.Escherichia coli cause the substantial majority of urinary tract infections (33). As a group, such uropathogenic isolates exhibit properties that are not prevalent among commensal E. coli isolates found in the intestinal flora (40). Prominent among these phenotypes is the expression of adhesins that mediate bacterial attachment to the human uroepithelium and thereby confer a selective advantage in ascending colonization of the upper urinary tract by allowing the bacteria to resist the cleansing effect of urine flow in the ureters (29). pap (pyelonephritis-associated pili) and prs (pap-related sequence) are two structurally and functionally related operon clusters that have been cloned from E. coli J96 and shown to express adhesin pili (9,21,22). pap encodes a P-fimbrial adhesin that specifically recognizes the globoseries of glycolipids present on both human erythrocytes bearing the P blood group antigen and uroepithelial cells (19,21,22). prs encodes an F adhesin that preferentially binds to the Forsmann antigen, which is a major constituent of sheep erythrocyte membranes and is also present on the cells of the human renal pelvis (21,22).In a recent s...

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