When "dead" isn't dead: VBNC entering and survival modeling of Salmonella Typhimurium ATCC 14028 in...

Salmonella can persist in low water activity (a_w) foods for years. This high resistance to conservation methods applied by the food industry makes this pathogen a public health concern. In this work, a predictive model to describe the survival of Salmonella enterica serovar Typhimurium ATCC 14028 under four different water activity (0.9, 0.8, 0.7 and 0.6 a_w) conditions was determined, in parallel with the determination of cell viability throughout and after exposure to stress to monitor the entry and persistence of this pathogen in the VBNC state. In addition, morphological changes in the cells at the beginning of the stress, before and after the loss of culturability, and on the last day of exposure to stress were analyzed. The Weibull model best described the survival of Salmonella Typhimurium under the tested conditions. Even after Salmonella Typhimurium reached the detection limits, viable cells were detected, indicating the presence of cells in the VBNC state. The population in the VBNC state was gradually formed throughout the exposure to stress, corresponding to all viable cells quantified by flow cytometry and visualized by fluorescence microscopy at the end of 30 and 45 days. Cells exposed at 0.6 a_w had a significant increase in cellular length, reaching 185% higher length size than the no stressed cells. The fact that the pathogen shows a relatively slow inactivation rate in highly osmotic environments and remains viable, even when it is undetectable by conventional techniques, may became Salmonella more resistant and promote its entrance into a VBNC state.