Production of enterotoxin, verotoxin, hemolysin and cytotoxic necrotizing factor by Escherichia coli of intestinal and extraintestinal origin

Effect of Escherichia coli cytotoxic necrotizing factor 1 on repair of human bladder cell monolayers in vitro

We hypothesized that Escherichia coli cytotoxic necrotizing factor 1 (CNF1) might impair migration or proliferation of bladder cells and could potentially interfere with repair of the bladder epithelium. Using experimentally wounded human T24 bladder epithelial cell monolayers as an in vitro model, we found that both the number of T24 cells and the maximum distance they migrated into wounded regions was significantly decreased by bacterial extracts containing E. coli CNF1.

Cytotoxicity of hemolytic, cytotoxic necrotizing factor 1-positive and -negative Escherichia coli to human T24 bladder cells

Approximately one-half of Escherichia coli isolates from patients with cystitis or pyelonephritis produce the pore-forming cytotoxin hemolysin, a molecule with the capacity to lyse erythrocytes and a range of nucleated cell types. A second toxin, cytotoxic necrotizing factor 1 (CNF1), is found in approximately 70% of hemolytic, but rarely in nonhemolytic, isolates. To evaluate the potential interplay of these two toxins, we used epidemiological and molecular biologic techniques to compare the cytotoxicity of hemolytic, CNF1(+), and CNF1(-) cystitis strains toward human T24 bladder epithelial cells in vitro. A total of 29 isolates from two collections of cystitis-associated E. coli were evaluated by using methylene blue staining of bladder monolayers at 1-h intervals after inoculation with each strain. Most (20 of 29) isolates damaged or destroyed the T24 monolayer (less than 50% remaining) within 4 h after inoculation. As a group, CNF1(+) isolates from one collection (11 strains) were less cytotoxic at 4 h than the CNF1(-) strains in that collection (P = 0.009), but this pattern was not observed among isolates from the second collection (18 strains). To directly evaluate the role of CNF1 in cytotoxicity of hemolytic E. coli without the variables present in multiple clinical isolates, we constructed mutants defective in production of CNF1. Compared to the CNF1(+) parental isolates, no change in cytotoxicity was detected in these cnf1 mutants. Our results indicate that CNF1 does not have a detectable effect on the ability of hemolytic E. coli to damage human bladder cell monolayers in vitro.