Food-borne enterococci and their resistance to oxidative stress.

Enterococci are important food-borne pathogens that cause serious infections. Several virulence factors have been described including aggregation substance, gelatinase, cytolysin, and enterococcal surface protein. The ability to cause infections is mainly dependent on the response to oxidative stress due to the production of reactive oxygen species by immune cells. The aim of our study was to analyze the resistance of enterococcal strains from food to clinically relevant antiseptic agents with regard to the presence of selected virulence factors, and to uncover potential mechanisms of the antioxidative resistance. Eighty-two enterococcal isolates from Bryndza cheese were tested using in vitro growth assays to study the ability of these isolates to survive exposure to antiseptic agents - hydrogen peroxide, hypochlorite, and Chlorhexidine. Virulence genotypes of the isolates were determined by PCR, and RT real time PCR was used for gene expression under oxidative stress. Resistance against antiseptic agents depends on the concentration of applied chemicals, on the time of exposure, but also on virulence factors of the enterococcal strains. Oxidative stress induces the expression of antioxidative enzymes and down-regulates the expression of prooxidative enzymes. These effects are dependent on the virulence genotype of the enterococcal strains. These findings are important for future research, especially concerning the role of enterococci in oral diseases.