Todd Kitten, Ph.D.

Todd Kitten, Ph.D.

Associate professor

Wood Memorial Building Link opens in new window
521 North 11th Street
Box 980566
Richmond, Virginia 23298-0566
Phone: (804) 628-7010
Fax: (804) 828-0150


  • Ph.D. in Microbiology and Immunology, University of Texas Health Science Center at San Antonio, 1992
  • B.A. in Biology, University of Dallas, 1986

Website: Kitten lab Link opens in new window


S. sanguinis cells within an infected heart valve

Research in our lab concerns bacteria that live in the mouth and their relationship to health and disease. We are particularly interested in Streptococcus sanguinis, an important primary colonizer of teeth and a frequent cause of a heart infection known as infective endocarditis. The picture at left shows a transmission electron micrograph of S. sanguinis cells within an infected heart valve.

Along with other investigators at VCU, we recently determined the DNA sequence of the S. sanguinis genome Link opens in new window. We have used this information to identify potential virulence factors for endocarditis, including 32 cell wall-anchored (also called "LPxTG") proteins and 52 lipoproteins. We have mutagenized the genes encoding each of these proteins and have tested the mutants for endocarditis virulence. LPxTG proteins function principally as adhesins and exoenzymes whereas lipoproteins function primarily in transport and post-translational modification. The figure below depicts these two classes of proteins.

Classes of proteins

We have found that the SsaB transport lipoprotein is particularly important for endocarditis virulence. Mutation of its gene results in a >1000-fold reduction in competitiveness in an endocarditis model. We are currently working to determine the mechanism by which SsaB contributes to disease.

S. sanguinis cells possess the ability to incorporate foreign DNA from their environment into their genome—a property known as genetic competence. The figure below illustrates the major components of the competence system in S. sanguinis.

Major components of the competence system in S. sanguinis

We are interested in examining this system because (i) competence likely plays an important role in genome evolution and adaptability (ii) the competence system likely possesses functions in addition to DNA uptake, including contributing to biofilm formation in dental plaque, and (iii) the system in S. sanguinis appears to possess important differences relative to characterized systems in other bacteria. We are currently examining the genetic regulation of the competence system, and its possible contribution to endocarditis virulence and biofilm formation.


Callahan JE, Munro CL, Kitten T. The streptococcus sanguinis competence regulon is not required for infective endocarditis virulence in a rabbit model. PLoS One. 2011;6:e26403
Kitten T, Turner LS, Xu P. Biological implications of the streptococcus sanguinis genome. In: Kolenbrander PE, ed. Oral microbial communities: Genomic inquiry and interspecies communication. Washington, D.C: ASM Press; 2011:43-61. 
Rodriguez AM, Callahan JE, Fawcett P, Ge X, Xu P, Kitten T. Physiological and molecular characterization of genetic competence in streptococcus sanguinis. Mol Oral Microbiol. 2011;26:99-116
Xu P, Ge XC, Chen L, Wang XJ, Dou YT, Xu JZ, Patel JR, Stone V, Trinh M, Evans K, Kitten T, Bonchev D, Buck GA. Genome-wide essential gene identification in streptococcus sanguinis. Sci Rep-Uk. 2011;1 
Das S, Kanamoto T, Ge X, Xu P, Unoki T, Munro CL, Kitten T. (2009) Contribution of lipoproteins and lipoprotein processing to endocarditis virulence in Streptococcus sanguinis. J. Bacteriol.: in press.

Ge X, Kitten T, Chen Z, Lee SP, Munro CL, Xu P. (2008) Identification of Streptococcus sanguinis genes required for biofilm formation and examination of their role in endocarditis virulence. Infect Immun 76:2551-2559.

Tang G, Kitten T, Munro CL, Wellman GC, Mintz KP. (2008) EmaA, a potential virulence determinant of Aggregatibacter (Actinobacillus) actinomycetemcomitans in infective endocarditis. Infect Immun 76:2316-2324.

Xu P, Alves JM, Kitten T, Power A, Chen Z, Manque P, Ge X, Serrano MG, Ozaki LS, Akan D, Hendricks S, Wang Y, Puiu D, Chaplin M, Paik S, Peterson DL, Macrina FL, Buck GA. (2007) Genome of the opportunistic pathogen Streptococcus sanguinis. J. Bacteriol. 189:3166-3175.

Paik S, Senty L, Das S, Noe JC, Munro CL, Kitten T. (2005) Identification of virulence determinants for endocarditis in Streptococcus sanguinis by signature-tagged mutagenesis. Infect Immun 73:6064-6074.

Das S, Noe JC, Paik S, Kitten T. (2005) An improved arbitrary primed PCR method for rapid characterization of transposon insertion sites. J Microbiol Methods 63: 89-94.