A role for hemolysin in Escherichia coli-induced inflammation in granulocytopenic rabbits

Pyelonephritogenic Escherichia coli and killing of cultured human renal proximal tubular epithelial cells: role of hemolysin in some strains

Acute pyelonephritis, a complication of Escherichia coli bacteriuria, must represent a bacterial invasion through the kidney epithelium. To study this process, we overlaid bacterial suspensions onto monolayers of cultured human kidney proximal tubular epithelial cells and measured cytotoxicity by release of lactate dehydrogenase (LDH). Thirty-four isolates cultured from patients with acute pyelonephritis were screened for the ability to cause pyelonephritis in CBA mice by transurethral challenge. The eight most virulent strains (greater than or equal to 70% of mice challenged developed greater than or equal to 10(3) CFU/g of kidney after 48 h) were selected for study. Each strain displayed mannose-resistant hemagglutination of human O erythrocytes; three strains were phenotypically and genotypically hemolytic. Pyelonephritogenic strains were significantly more cytotoxic (30.1 +/- 9.5% LDH release after 18 h) than eight fecal control strains (13.5 +/- 11.5% LDH release; P = 0.0068). We selected the most cytotoxic strain, CFT073, for further study. Sterile filtrate from this hemolytic strain was significantly more cytotoxic than was the filtrate of the fecal control strain, FN414. Transposon mutagenesis of CFT073 with TnphoA abolished hemolytic activity and cytotoxicity by both whole cells and sterile filtrate. Southern blot analysis revealed that the Tnphoa insertion mapped to the E. coli chromosomal hly determinant within a 12-kilobase SalI restriction fragment. Transformation of a nonhemolytic strain, CPZ005 with plasmid pSF4000, which carries a cloned hemolysin determinant, resulted in highly elevated cytotoxicity. Light micrographs of proximal tubular epithelial cell cultures demonstrated cell damage by pyelonephritogenic strains that was not induced by a fecal strain or the hemolysin-deficient mutant. Results indicate that pyelonephritogenic E. coli strains are more frequently cytotoxic for a putative target, that is, human renal tubular epithelium, than are fecal isolates. Hemolysin, in some strains, is apparently responsible for this cytotoxicity.

Influence of cloned Escherichia coli hemolysin genes, S-fimbriae and serum resistance on pathogenicity in different animal models

The virulence of the uropathogenic E. coli strain 536 (O6:K15:H31) which produces the S-fimbrial adhesin (Sfa+), is serum-resistant (Sre+) and hemolytic (Hly+) and its derivatives were assessed in five different animal models. Cloned hemolysin (hly) determinants from the chromosomes of O6, O18 and O75 E. coli strains and from the plasmid pHly152 were introduced into the spontaneous Sfa-, Sre-, Hly- mutant 536-21 and its Sfa+, Sre+, Hly- variant 536-31. As already demonstrated for the 536-21 strains (Infect. Immun. 42: 57-63) the O18-hly determinant but not the plasmid-encoded hly determinant of pHly152 transformed into 536-31 contribute to lethality in a mouse peritonitis model. Similar results were obtained with both Hly- host strains and their Hly+ transformants in a chicken embryo test and in a mouse nephropathogenicity assay in which the renal bacterial counts were measured 15 min to 8 hours after i.v. infection. S-fimbriae and serum resistance had only a marginal influence in these three in vivo systems. In contrast all three factors, S-fimbriae, serum resistance and hemolysin, were necessary for full virulence in a respiratory mouse infection assay. In a subcutaneously-induced sepsis model in the mouse restoration of S-fimbriae and serum resistance and separately chromosomally-encoded hemolysis increased virulence to a level comparable to that of the parental 536 strain.