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Infect Immun, May 1998, p. 2180-2185, Vol. 66, No. 5
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Inactivation of the gbpA Gene of Streptococcus mutans Increases Virulence and Promotes In Vivo Accumulation of Recombinations between the Glucosyltransferase B and C Genes

Karsten R. O. Hazlett,1,* Suzanne M. Michalek,2 and Jeffrey A. Banas1

Department of Microbiology, Immunology, and Molecular Genetics, Albany Medical College, Albany, New York 12208,1 and Department of Microbiology, The University of Alabama at Birmingham, Birmingham, Alabama 352942

Received 7 November 1997/Returned for modification 20 January 1998/Accepted 2 February 1998

Glucan-binding protein A (GbpA) of Streptococcus mutans has been hypothesized to promote sucrose-dependent adherence and the cohesiveness of plaque and therefore to contribute to caries formation. We have analyzed the adherence properties and virulence of isogenic gbpA mutants relative to those of wild-type S. mutans. Contrary to expectations, the gbpA mutant strains displayed enhanced sucrose-dependent adherence in vitro and enhanced cariogenicity in vivo. In vitro, S. mutans was grown in the presence of [3H]thymidine and sucrose within glass vials. When grown with constant rotation, significantly higher levels of gbpA mutant organisms than of wild type remained adherent to the vial walls. Postgrowth vortexing of rotated cultures significantly decreased adherence of wild-type organisms, whereas the adherence of gbpA mutant organisms was unaffected. In the gnotobiotic rat model, the gbpA mutant strain was hypercariogenic though the colonization levels were not significantly different from those of the wild type. The gbpA mutant strain became enriched in vivo with organisms that had undergone a recombination involving the gtfB and gtfC genes. The incidence of gtfBC recombinant organisms increased as a function of dietary sucrose availability and was inversely correlated with caries development. We propose that the absence of GbpA elevates the cariogenic potential of S. mutans by altering the structure of plaque. However, the hypercariogenic plaque generated by gbpA mutant organisms may be suboptimal for S. mutans, leading to the accumulation of gtfBC recombinants whose reduced glucosyltransferase activity restores a less cariogenic plaque structure.

* Corresponding author. Mailing address: Department of Microbiology, Immunology, and Molecular Genetics, Albany Medical College, Albany, NY 12208. Phone: (518) 262-6513. Fax: (518) 262-5748. E-mail: KHazlett{at}aol.com.

Infect Immun, May 1998, p. 2180-2185, Vol. 66, No. 5
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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