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Infect Immun, July 1998, p. 3384-3389, Vol. 66, No. 7
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Cytotoxicity of Hemolytic, Cytotoxic Necrotizing Factor 1-Positive and -Negative Escherichia coli to Human T24 Bladder Cells

Michael D. Island,1,* Xiaoling Cui,1 Betsy Foxman,2 Carl F. Marrs,2 Walter E. Stamm,3 Ann E. Stapleton,3 and John W. Warren1

Division of Infectious Diseases, Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland1; Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor, Michigan2; and Division of Allergy and Infectious Diseases, Department of Medicine, University of Washington, Seattle, Washington3

Received 8 December 1997/Returned for modification 19 January 1998/Accepted 1 April 1998

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.

* Corresponding author. Mailing address: Department of Medicine, Division of Infectious Diseases, University of Maryland School of Medicine, 10 South Pine St., Baltimore, MD 21201-1192. Phone: (410) 706-7560. Fax: (410) 706-8700. E-mail: misland{at}umaryland.edu.

Infect Immun, July 1998, p. 3384-3389, Vol. 66, No. 7
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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