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Infection and Immunity, November 1999, p. 5898-5905, Vol. 67, No. 11
Division of Geographic Medicine and
Infectious Diseases, Tufts-New England Medical Center and Tufts
University School of Medicine, Boston, Massachusetts 02111
Received 17 May 1999/Returned for modification 14 July
1999/Accepted 10 August 1999
Horizontal transfer of genes encoding virulence factors has played
a central role in the evolution of many pathogenic bacteria. The
unexpected discovery that the genes encoding cholera toxin (ctxAB), the main cause of the profuse secretory diarrhea
characteristic of cholera, are encoded on a novel filamentous phage
named CTX
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Alternative Mechanism of Cholera Toxin Acquisition by
Vibrio cholerae: Generalized Transduction of CTX
by
Bacteriophage CP-T1
, has resulted in a renewed interest in the potential
mechanisms of transfer of virulence genes among Vibrio
cholerae. We describe here an alternative mechanism of cholera
toxin gene transfer into nontoxigenic V. cholerae
isolates, including strains that lack both the CTX
receptor, the
toxin coregulated pilus (TCP), and attRS, the chromosomal
attachment site for CTX
integration. A temperature-sensitive mutant
of the V. cholerae generalized transducing bacteriophage CP-T1 (CP-T1ts) was used to transfer a genetically marked derivative of the CTX prophage into four nontoxigenic
V. cholerae strains, including two V. cholerae
vaccine strains. We demonstrate that CTX
transduced by CP-T1ts can
replicate and integrate into these nontoxigenic V. cholerae
strains with high efficiency. In fact, CP-T1ts transduces the CTX
prophage preferentially when compared with other chromosomal
markers. These results reveal a potential mechanism by which
CTX
+ V. cholerae strains that lack the
TCP receptor may have arisen. Finally, these findings indicate an
additional pathway for reversion of live-attenuated V. cholerae vaccine strains.
*
Corresponding author. Mailing address: Division of
Geographic Medicine/Infectious Disease, Tufts-New England Medical
Center, 750 Washington St., Boston, MA 02111. Phone: (617) 636-7618. Fax: (617) 636-5292. E-mail:
matthew.waldor{at}es.nemc.org.
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