Membrane fluidity-related adaptive response mechanisms of foodborne bacterial pathogens under environmental stresses

The maintenance of bacterial membrane fluidity plays an important role in a variety of cell physiological functions such as nutrient transport, protection from external adverse environments, and cell morphology. The fluidity of membranes is modified in response to several environmental cues, enabling bacterial survival in otherwise unfavorable conditions. Many foodborne bacterial pathogens are able to survive a variety of food preservation treatments used to prevent microbial contamination. These pathogens are able to successfully exploit membrane fluidity-related adaptation strategies under unfavorable conditions, resulting in food hygiene failures. Factors involved in food preservation include pH, temperature, osmotic stress, antimicrobial agents, and high pressure. The fluidity of bacterial membrane lipid bilayer is altered mainly via the adjustment of membrane fatty acid composition. Under undesirable conditions, Gram-negative bacteria alter their membrane fluidity primarily by regulating the ratio of unsaturated fatty acids (UFAs) to saturated fatty acids (SFAs) and, to a lesser extent, the levels of cyclopropane fatty acids (CFAs), or by cis/trans isomerization. Gram-positive bacteria typically alter their membrane fluidity with changes in fatty acyl chain length or by forming branched-chain fatty acids (BCFAs), besides changes to the ratio of UFA to SFA. This review encompasses various modulators of membrane fluidity, particularly with respect to foodborne pathogens, which often survive even the hostile environments associated with food processing.