P1-75 Environmental Adaptation and Stress Response Mechanisms of Salmonella enterica in Peanut Oil, Peanuts and Chia Seeds

Sunday, July 26, 2015
Exhibit Hall (Oregon Convention Center)
Karen Fong , MSc. student , Vancouver , Canada
Siyun Wang , The University of British Columbia , Vancouver , Canada
Introduction: Outbreaks of Salmonella in recent years have been linked to an assortment of low-water activity (aw) foods, such as nuts, peanut butter and chia seed powder. The unusual emergence in environments that should otherwise promote death highlights the need for elucidation of response networks that enhance survival.

Purpose: The purpose of this study is to evaluate the response of Salmonella enterica to two stressors commonly encountered in low-afood processing, desiccation and heat.

Methods:  Five serotypes of S. enterica were desiccated in three food matrices with varying aw: peanut oil (aw = 0.560), peanuts (aw = 0.330) and chia seeds (aw = 0.585) to identify survival characteristics in low-aw environments. Oil-desiccated cells were subsequently used in heat experiments to identify cross-protective mechanisms. In these assays, tolerance to lethal heat at 70°C following six-day oil desiccation was evaluated. Survival at 70°C following exposure to a sub-lethal heat of 45°C was also assessed. 

Results: S. enterica exhibited serotype-specific differences in survival capabilities in the low-aw foods. Serotypes Hartford and Tennessee demonstrated an aggressive phenotype across all three low-afoods, while Typhimurium was identified as the least aggressive serotype.  Interestingly, persistent serotypes survived to upwards of 90 days in peanut oil.  Exposure to 70°C following six-day oil desiccation revealed significantly (P < 0.05) higher concentrations in all serotypes compared to non-desiccated controls.  Moreover, significantly (P < 0.05) higher concentrations were observed following pre-adaptation to 45°C. 

Significance: These results indicate that S. enterica is capable of long-term desiccation in low-aw foods and can lead to enhanced resistance to heat treatments. These are problematic to the food industry, which often use these two hurdles in tandem to reduce Salmonella contamination.