Expression of virulence-related genes by Enterococcus faecalis in response to different environments

Enterococci are ubiquitous organisms used to both improve the flavor and texture of fermented foods, and provide protective mechanisms as either a probiotic or antimicrobial additive. However, two species, E. faecalis and E. faecium, are also associated with 10% of nosocomial infections of the bloodstream, wounds, urinary tract and heart. While the genes involved in the pathogenicity of these organisms are slowly identified along with the mechanisms behind their regulation, the environmental signals involved in the conversion to pathogenicity remain unclear. The distribution of virulence genes was determined in 13 E. faecalis isolates from medical, food and animal sources. Regardless of their source of isolation, all isolates harbored between eight and thirteen virulence genes. Relative differences in expression of the virulence associated genes clpP, clpX, gls24, agg, efaA, gelE, and cylBL(L) were examined in E. faecalis TMW 2.63 and TMW 2.622 exposed to different environments (LB, BHI, respective supernatants, pig fecal extract, LB+6.5% NaCl, LB+pH5, LB+6.5% NaCl+pH5, and sausage medium) using RT-PCR and Lightcycler technology. Significant differences in expression were influenced by growth phase, environment, and isolate, which suggests that these three factors be taken into consideration during the selection of enterococci for use in foods or as probiotics rather than their source of isolation or set of virulence genes.