Inactivation of Salmonella Enteritidis strains by combination of high hydrostatic pressure and nisin.

The effects of high hydrostatic pressure (HHP) and nisin treatment alone and in combination on cellular components and viability of two Salmonella enterica subsp. enterica serovar Enteritidis (S. Enteritidis) strains were evaluated by differential scanning calorimetry (DSC) and plate counting in order to evaluate the relative resistance and optimize the treatment conditions. S. Enteritidis FDA and OSU 799 strains were subjected to HHP (0.1-550 MPa for 10 min at 25 degrees C) alone and in combination with nisin (200 IU/ml nisin) in culture broth. HHP (up to 200 MPa) or the nisin alone did not affect the viability and cellular components of either strain. An 8-log cfu/ml reduction was observed after a pressure treatment at 500 MPa for the FDA strain and 450 MPa for the OSU 799 strain. When nisin was added, a similar reduction was obtained at 400 MPa for FDA strain and 350 MPa for the OSU 799 strain. The decrease in apparent enthalpy appeared to be mainly due to reduction in the ribosome denaturation peak for both the pressure alone and the pressure-nisin combination treatments. HHP facilitated penetration of nisin into the cell above 100 MPa pressure. Monitoring through DNA-binding probes the effect of pressure and nisin treatments on DNA in vivo showed that nisin did not affect DNA at 200 IU/ml. The apparent enthalpy data obtained from DSC can be used for optimization of pressure levels to reduce a microbial population in the presence of nisin.