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Infect Immun, May 1998, p. 2040-2051, Vol. 66, No. 5
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Characterization of the Roles of Hemolysin and Other Toxins in Enteropathy Caused by Alpha-Hemolytic Escherichia coli Linked to Human Diarrhea

Simon J. Elliott,1,2,* S. Srinivas,3 M. John Albert,4 Khorshed Alam,4 Roy M. Robins-Browne,5 Stuart T. Gunzburg,2 Brian J. Mee,2 and Barbara J. Chang2

Center for Vaccine Development1 and Department of Comparative Medicine and Pathology,3 University of Maryland School of Medicine, Baltimore, Maryland 21201; International Center for Diarrheal Disease Research, Dhaka, Bangladesh4; and Department of Microbiology, The University of Melbourne, Parkville, Victoria 3052,5 and Department of Microbiology, The University of Western Australia, Nedlands, Western Australia 6009,2 Australia

Received 5 September 1997/Returned for modification 23 October 1997/Accepted 29 January 1998

Escherichia coli strains producing alpha-hemolysin have been associated with diarrhea in several studies, but it has not been clearly demonstrated that these strains are enteropathogens or that alpha-hemolysin is an enteric virulence factor. Such strains are generally regarded as avirulent commensals. We examined a collection of diarrhea-associated hemolytic E. coli (DHEC) strains for virulence factors. No strain produced classic enterotoxins, but they all produced an alpha-hemolysin that was indistinguishable from that of uropathogenic E. coli strains. DHEC strains also produced other toxins including cytotoxic necrotizing factor 1 (CNF1) and novel toxins, including a cell-detaching cytotoxin and a toxin that causes HeLa cell elongation. DHEC strains were enteropathogenic in the RITARD (reversible intestinal tie adult rabbit diarrhea) model of diarrhea, causing characteristic enteropathies, including inflammation, necrosis, and colonic cell hyperplasia in both small and large intestines. Alpha-hemolysin appeared to be a major virulence factor in this model since it conferred virulence to nonpathogenic E. coli strains. Other virulence factors also appear to be contributing to virulence. These findings support the epidemiologic link to diarrhea and suggest that further research into the role of DHEC and alpha-hemolysin in enteric disease is warranted.


* Corresponding author. Mailing address: Center for Vaccine Development, University of Maryland School of Medicine, 685 W Baltimore St., Baltimore, MD 21201. Phone: (410) 706 2493. Fax: (410) 706 6205. E-mail: selliott{at}umaryland.edu.


Infect Immun, May 1998, p. 2040-2051, Vol. 66, No. 5
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.



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