Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/23/2003
Publication Date: 2/1/2004
Citation: Bayles, D.O. Changes in thermal sensitivity resulting from ph and nutritional shifts of acid adapted and non-acid adapted salmonella enterica serovar typhimurium dt104. Journal of Food Protection.
Interpretive Summary: It is known that bacteria respond to their surroundings in an effort to survive and grow; however, it is not well understood how these adaptations affect our ability to destroy bacteria in foods during heating. It is also unclear how the food composition itself alters our ability to destroy bacteria that contaminate foods. To better understand these interactions, Salmonella enterica var. Typhimurium was acid adapted, and both acid adapted and nonacid adapted bacteria were subsequently heat treated in a combination of media that simulated different food conditions. The surviving fraction of cells remaining was enumerated at time points throughout the heat treatment. The survivor curve data was statistically analyzed using D-values and a modeling approach that treats survivor curves as a cumulative distribution of lethal events. Analyses of the results uncovered the effects and interactions that nutrient availability, glucose (sugar) availability, and low or neutral pH had on the ability to destroy S. Typhimurium with heat. Information on these effects and interactions helps to reveal food conditions that may require additional interventions to assure safety and may also lead to changes that can be incorporated into foods that will improve the effectiveness of current interventions.
Technical Abstract: Stationary phase Salmonella enterica var. Typhimurium DT104 cells that were either pH-dependent acid adapted or non-acid adapted, were heat challenged at 58C in a 2 x 2 x 2 factorial matrix consisting of fresh and conditioned tryptic soy broth (TSB) media, with and without 1% glucose, and pH 4.8 and pH 7. The resulting survivor curves were used to determine the D58 of the cells at the different treatment conditions. The survivor curves were also modeled to derive estimates for the heat resistance distribution inherent in the treated population. Analysis of the D58-values indicated that acid adapted cells were more thermally resistant than non-acid adapted cells (mean D58 = 0.94 min, D58 = 0.75 min, respectively). Comparison of modeled data and the D-value data revealed that changes in the D-value were not always positively correlated with changes in the mean and mode for the heat resistance distribution, but that D-value changes were strongly influenced by changes in the variance and skewness of the heat resistance distribution. The variance in the modeled heat distribution data was greater for acid adapted cells, while the skewness was greater for non-acid adapted cells. These data indicated that the presence and level of cross protection is highly dependent on both the physiological state of the cells and on the characteristics of the environment the cells are in at the time of thermal challenge. It is important to consider both the physiological state of the pathogen and the characteristics of the food to insure that stressed food borne pathogens are destroyed or inactivated.