sigB absence decreased Listeria monocytogenes EGD-e heat resistance but not its Pulsed Electric Fields resistance

This study shows the behaviour of Listeria monocytogenes under heat and Pulsed Electric Fields (PEF) treatments, as well as the influence of sigB in bacterial resistance and recovery. Absence of the sigB gene resulted in a decreased heat tolerance, showing that σB influences L. monocytogenes heat survival. Heat treatments at 60 °C (40 s) caused sublethal membrane injuries in 99.99% of survivors. The repair of heat damage required energy production and lipid, protein, and RNA synthesis, and it lasted 6 h. Furthermore, deletion of sigB did not affect the heat injuries repair. PEF resistance at pH 4.0 and 7.0 was not influenced by sigB. Sublethal damage after PEF treatments was only detected when PEF-treated cells had previously been heat-shocked (45 °C/1 h). The membrane repair only required energy production, and it was independent of sigB. Although both heat and PEF treatments have an effect on cellular membrane, the repair of the sublethal damages suggests different membrane targets, and thus we propose a different mechanism of inactivation by these food preservation technologies.