Temperature-mediated variations in cellular membrane fatty acid composition of Staphylococcus aureus in resistance to pulsed electric fields.

Effects of growth temperature on cell membrane fatty acid composition, fluidity and lethal and sublethal injury by pulsed electric fields (PEF) in Staphylococcus aureus ATCC 43300 (S. aureus) in the stationary phase were investigated. Analysis of the membrane fatty acids by gas chromatography-mass spectrometry (GC-MS) revealed that branched chain fatty acids (iso C14:0, iso C15:0, anteiso C15:0 and anteiso C17:0) and straight chain fatty acids (C12:0, C14:0, C16:0, C17:0 and C18:0) were primary constituents in the membrane. The S. aureus changed its membrane fatty acid composition and its overall fluidity when exposed to different temperatures. The PEF lethal and sublethal effects were assessed, and results suggested that the degree of inactivation depended on the cell membrane structure, electric field strength and treatment time. The PEF inactivation kinetics including lethal and sublethal injury fractions were fitted with non-linear Weibull distribution, suggesting that inactivation of the first log cycle of S. aureus population was significantly affected by growth temperature, and the membrane of cells became more fluid, and easier to induce electroportion in low temperatures. Moreover, the morphology of S. aureus cells were investigated by electron microscopy, showing that various temperature-modified cells were distorted to differing extents and some even collapsed due to deep irreversible electroporation after PEF treatment.