Virulence of Listeria monocytogenes before and after high hydrostatic pressure treatment

High hydrostatic pressure treatment is regarded as a possible alternative process for food preservation. One of the primary considerations for industrial applications is the ability of this technique to destroy pathogenic microorganisms. The inactivation of microorganism populations after high pressure treatment is well described, but their residual pathogenicity is less documented. This study compared the virulence of Listeria monocytogenes scott A before and after high pressure treatments. The pressurized samples were composed of 1 ml of Listeria monocytogenes culture diluted into 9 ml of buffer. Two buffers are used: phosphate buffer (pH 7) and citrate buffer (pH 5.6). The virulence of cells is estimated by their association and invasion capacities to Hela cells. These characteristics of pathogenity were compared between untreated and pressurized cells (400 MPa, 10 min, in citrate buffer) or (600 MPa, 10 min, in phosphate buffer). These results showed that, after treatment in citrate buffer, the treated cells lost their association and invasion capacities. However, in a phosphate buffer, treated cells have lose their invasion properties, but retain their association capacities to Hela cells. These results showed that the inactivation of Listeria monocytogenes population involve a loss of their pathogenic properties. However, the conservation of association capacities of some inactivated cells show that these cells seem to continue to express adhesion molecules and, in certain conditions, can re-establish their multiplication properties.