Effect of periodic fluctuation in the osmotic environment on the adaptation of Salmonella.

The growth of Salmonella from different osmotic histories was studied in low water activity conditions. Cell cultures were successively diluted and grown in batch, in minimal medium, without and then with added NaCl, several times and from different inoculum levels. The viable count curves obtained in low water activity conditions showed an initial decline after which the culture either died out or recovered and entered the exponential phase. After the first batch with NaCl added, the subsequent curves at low water activity showed progressively smaller initial decline and shorter lag time as the number of transfers from high to low water activity conditions increased. The observed curves were analyzed by F-tests applying an extension of the model of Baranyi and Roberts (1994). The results suggest that periodic, systematic "training" can improve the adaptation capability of the organism without resulting in higher specific growth rate.