Virulence of Enterococcus faecalis dairy strains in an insect model: the role of fsrB and gelE

Abstract

Despite the existence of various virulence factors in theEnterococcusgenus, enterococcal virulence is still a debated issue. A main consideration is the detection of the same virulence genes in strains isolated from nosocomial or community-acquired infections, and from food products. The goal of this study was to evaluate the roles of two well-characterized enterococcal virulence factors, Fsr and gelatinase, in the potential virulence ofEnterococcus faecalisfood strains. Virulence of unrelatedEnterococcusisolates, including dairy strains carryingfsrandgelEoperons, was compared in theGalleria mellonellainsect model.E. faecalisdairy strains were able to kill larvae and were as virulent as strain OG1RF, one of the most widely used for virulence studies. In contrast,Enterococcus duransandEnterococcus faeciumstrains were avirulent or poorly virulent forG. mellonella. To evaluate the role offsrBandgelEin virulence ofE. faecalisdairy strains, both genes were deleted independently in two strains. The ΔfsrBand ΔgelEdeletion mutants both produced a gelatinase-negative phenotype. Although both mutations significantly attenuated virulence inG. mellonella, the ΔfsrBstrains were more strongly attenuated. These results agree with previous findings suggesting the involvement offsrBin the control of other cell functions relevant to virulence. Our work demonstrates that the presence of functionalfsrB, and to a lesser extentgelE, in dairy enterococci should be considered with caution.