The susceptibility of injured cells to selective media may be related, among others, to membrane damage Loss of tolerance to the presence of sodium chloride in plating media is attributed
to damage to the functionality and/or integrity of the cytoplasmic membrane, thus preventing microbial growth on the corresponding NaClbased selective media Selective media to detect ublethal membrane impairment should contain the highest concentration of sodium chloride that does not inhibit the growth of non-stressed cells Formulation of selective media with lower/higher NaCl concentrations would result in under/overestimation of sublethally injured cell populations. However, there is a lack of consensus in the literature on the appropriate levels of sodium chloride to formulate these selective media The maximum non-inhibitory NaCl concentration in the plating medium depends not only on the microbial strain, but also on the growth phase and the physiological state of the NaCl-exposed cells In this sense, stationary phase cells oftenwithstand stress scenarios (e.g. hyperosmotic NaCl stress) better than exponentially growing populations due to the de novo synthesis of stress proteins in the early stationary phase Several common shock proteins have been reported to be synthesized after exposure to osmotic stress and during starvation at the stationary phase of growth Whereas the stationary phase of growth is the most often encountered in a natural environment , planktonic growth is not the natural state for bacteria in their normal habitats, for instance food products, which exhibit a solid structure that leads to surface/submerged colony growth Planktonic or freely-suspended cells are routinely used to investigate microbial inactivation/SI mechanisms, although, they often exhibit different susceptibility to inhibitory agents (e.g. NaCl) compared to cell colonies, which are also subjected to immobilization stress