Influence of naringenin adaptation and shock on resistance of Staphylococcus aureus and Escherichia coli to pulsed electric fields

This work was aimed to investigate the stress induced by naringenin, one of the natural antibacterial components in citrus plants on the resistance of Staphylococcus aureus ATCC 6538 and Escherichia coli ATCC 25922 cells to pulsed electric fields (PEF). The results revealed that Staphylococcus aureus and Escherichia coli subjected to naringenin shock (2.0 h) did not significantly change their resistance to the subsequent PEF treatment. However, naringenin adaptation of Staphylococcus aureus and Escherichia coli cells decreased their resistance by exhibiting higher inactivation levels with more damage in cell membrane integrity and more morphological change after being exposed to PEF treatment. This difference in response to PEF treatment for Staphylococcus aureus and Escherichia coli might be due to the difference in the alterations of membrane fatty acids during preliminary naringenin exposure. Staphylococcus aureus adapted to naringenin remarkably increased the content of anteiso-branched chain fatty acids and simultaneously decreased the levels of straight and iso-branched chain fatty acids, whereas Escherichia coli cells caused a significant increase of unsaturated fatty acids at the expense of saturated and cyclic fatty acids. Comparatively, no significant changes were observed in the membrane fatty acid composition of cells after being subjected to naringenin shock.