A genetic exploration reveals novel Streptococcus pyogenes virulence factors important for in vivo survival and biofilm formation
Streptococcus pyogenes is an important human pathogen that can respond and adapt to changing environments. Although in vitro analyses have proven invaluable in determining specific streptococcal virulence factors, such studies are limited in their ability to provide a natural environment in which the invading pathogen responds directly, as well as indirectly, to the host conditions and defense systems. The goal of this study was to identify S. pyogenes virulence genes important for the pathogenesis of invasive disease using a large-scale genomic screen. Currently there are no reports in the literature of this technique being applied to S. pyogenes. Moreover, a novel animal model, the zebrafish, was used, which has been proven to mimic the responses involved in human streptococcal infection. Among the determinants identified in the screen were two separate macrolide efflux pumps with multiple insertions, indicating that they are significant factors in this type of invasive disease. Although many studies have examined the functions of these pumps in antibiotic resistance, there are no reports that directly correlate macrolide efflux proteins in S. pyogenes with virulence. Therefore, one of the foci of this study was to delineate the roles that they play in the establishment and progression of infection. Characterization of one of the efflux pumps, mefE, has revealed that it has a role in biofilm formation. A mutant strain with an insert in mefE is unable to form biofilms as compared to the wildtype strain in in vitro experiments as well as in our zebrafish model. Furthermore, a mutant strain which is hypothesized to upregulate not only mefE, but also the gene directly upstream of it, increases biofilm formation as compared to wildtype. The implications of this work are directly relevant to efforts in better understanding severe S. pyogenes diseases as high mortality rates persist despite traditional antibiotic therapy and surgical debridement. The importance of this study is underscored by the fact that the variety and severity of S. pyogenes infections are on the rise worldwide. Therefore, novel strategies are necessary and can only be accomplished with the aid of in vivo analyses in determining the molecular mechanisms involved in S. pyogenes pathogenesis.^
Anne E Kizy,
"A genetic exploration reveals novel Streptococcus pyogenes virulence factors important for in vivo survival and biofilm formation"
(January 1, 2008).
ETD Collection for Wayne State University.