Two-component system response regulators involved in virulence of Streptococcus pneumoniae TIGR4 in infective endocarditis.

Streptococci resident in the oral cavity have been linked to infective endocarditis (IE). While other viridans streptococci are commonly studied in relation to IE, less research has been focused on Streptococcus pneumoniae. We established for the first time an animal model of S. pneumoniae IE, and examined the virulence of the TIGR4 strain in this model. We hypothesized that two-component systems (TCS) may mediate S. pneumoniae TIGR4 strain virulence in IE and examined TCS response regulator (RR) mutants of TIGR4 in vivo with the IE model. Thirteen of the 14 RR protein genes were mutagenized, excluding only the essential gene SP_1227. The requirement of the 13 RRs for S. pneumoniae competitiveness in the IE model was assessed in vivo through use of quantitative real-time PCR (qPCR) and competitive index assays. Using real-time PCR, several RR mutants were detected at significantly lower levels in infected heart valves compared with a control strain suggesting the respective RRs are candidate virulence factors for IE. The virulence reduction of the ΔciaR mutant was further confirmed by competitive index assay. Our data suggest that CiaR is a virulence factor of S. pneumoniae strain TIGR4 for IE

<i>In vivo</i> competitive index analyses of Δsp_0798.

<p>The CFU of both strains collected from vegetations are shown. The geometric mean CI value calculated for the Δsp_0798 mutant was 0.09. The statistical significance as determined by one-sample t test was <i>P</i><0.01.</p

Primers used for mutant construction.

<p>Primers used for mutant construction.</p

<i>In vitro</i> growth of RR mutants.

<p>Growth of all 13 RR mutants with Erm-resistance cassettes, and control mutant Δsp_1678 with Erm- and Km-resistance cassettes. Bacterial cultures were individually grown at 37°C in microaerophilic conditions over the course of 10 hrs. Growth was measured by OD readings at 4 hrs and every hour thereafter on a FLUOstar plate reader at 600 nm.</p