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Infection and Immunity, September 2001, p. 5626-5634, Vol. 69, No. 9
0019-9567/01/$04.00+0   DOI: 10.1128/IAI.69.9.5626-5634.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Characterization of Haemophilus ducreyi cdtA, cdtB, and cdtC Mutants in In Vitro and In Vivo Systems

David A. Lewis,1,2 Marla K. Stevens,1 Jo L. Latimer,1 Christine K. Ward,1 Kaiping Deng,1 Robert Blick,1 Sheryl R. Lumbley,1 Catherine A. Ison,3 and Eric J. Hansen1,*

Department of Microbiology,1 University of Texas Southwestern Medical Center, Dallas, Texas 75235-9048,1 and Department of Genitourinary Medicine and Communicable Disease2 and Department of Microbiology,3 Imperial College School of Medicine, St. Mary's Campus, London W2 1PG United Kingdom

Received 12 May 2000/Returned for modification 19 June 2000/Accepted 13 June 2001

Haemophilus ducreyi expresses a soluble cytolethal distending toxin (CDT) that is encoded by the cdtABC gene cluster and can be detected in culture supernatant fluid by its ability to kill HeLa cells. The cdtA, cdtB, and cdtC genes of H. ducreyi were cloned independently into plasmid vectors, and their encoded proteins expressed singly or in various combinations in an Escherichia coli background. All three gene products had to be expressed in order for E. coli-derived culture supernatant fluids to demonstrate cytotoxicity for HeLa cells. Isogenic H. ducreyi cdtA and cdtB mutants were constructed and used in combination with the wild-type parent strain and a previously described H. ducreyi cdtC mutant (M. K. Stevens, J. L. Latimer, S. R. Lumbley, C. K. Ward, L. D. Cope, T. Lagergard, and E. J. Hansen, Infect. Immun. 67:3900-3908, 1999) to determine the relative contributions of the CdtA, CdtB, and CdtC proteins to CDT activity. Expression of CdtA, CdtB, and CdtC appeared necessary for H. ducreyi-derived culture supernatant fluid to exhibit cytotoxicity for HeLa cells. Whole-cell sonicates and periplasmic extracts from the cdtB and cdtC mutants had no effect on HeLa cells, whereas these same fractions from a cdtA mutant had a very modest cytotoxic effect on these same human cells. CdtA appeared to be primarily associated with the H. ducreyi cell envelope, whereas both CdtB and CdtC were present primarily in the soluble fraction from sonicated cells. Both the cdtA mutant and the cdtB mutant were found to be fully virulent in the temperature-dependent rabbit model for experimental chancroid.

* Corresponding author. Mailing address: Department of Microbiology, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, Texas 75390-9048. Phone: (214) 648-5974. Fax: (214) 648-5905. E-mail: eric.hansen{at}utsouthwestern.edu.

Infection and Immunity, September 2001, p. 5626-5634, Vol. 69, No. 9
0019-9567/01/$04.00+0   DOI: 10.1128/IAI.69.9.5626-5634.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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