Exploring the mechanisms of Staphylococcus aureus pulsed electric fields resistance acquisition after exposure to heat and alkaline shocks

This study aimed to acquire a deeper knowledge of the mechanisms of PEF resistance development after the exposure of Staphylococcus aureus to sublethal alkaline and heat shocks, with a particular focus on the modifications of cell envelope properties and their impact on electroporation and its reversion. Both shocks significantly (p < 0.05) increased the surface negative charge but they barely affected surface hydrophobicity or membrane fluidity. This resulted in an increased electroporation threshold (≈ 2 kV/cm) for alkaline-shocked but not for heat-shocked cells. Heat and alkaline shock-dependent development of PEF resistance did not require de novo RNA, protein, or lipid synthesis. Addition of nisin (100 UI/mL) to the treatment medium not only counteracted the protective effect of sublethal shocks against PEF, but even increased the lethality of PEF treatments (up to8.9-fold increase in Log cycles of inactivation) against heat-shocked and alkaline-shocked cells. This work contributed to a deeper understanding of the mechanisms leading to the development of PEF resistance, which is essential for PEF process optimization and for the design of PEF-based combined processes for food decontamination or pasteurization.