Prior Exposure to High Fat Content and Low Water Activity Improves the Survival of Salmonella enterica Tennessee in a Simulated Gastrointestinal System

Introduction: A surge of documented foodborne outbreaks caused by Salmonella enterica serovars have been linked to foods with high fat content and low water activities (a_w). The low a_w (0.3) of peanut butter limits the growth of Salmonella in the product; however, illnesses are reported from peanut butter contaminated with very small doses, suggesting the infectious dose of Salmonella is much lower when delivered in peanut butter.

Purpose: The purpose of our study was to quantify the survival of Salmonella exposed to peanut butter with different fat content and water activities after prolonged storage and after passage through a simulated gastrointestinal system.

Methods: S. enterica Tennessee (the strain from the 2006-2007 peanut butter outbreak) was inoculated into four peanut butter treatments (high fat, high a_w; high fat, low a_w; low fat, high a_w; low fat, low a_w) and then challenged with the simulated conditions of the gastrointestinal tract.

Results: Salmonella survival after in vitro digestion was influenced primarily by the fat content of the peanut butter. High fat/high a_w and high fat/low a_w peanut butter had a 2.4-log and 2.0-log increases in numbers, respectively, while low fat with both high and low a_w peanut butter peanut butter had 1.2-log reductions in cell count (P < 0.02).

Significance: Further studies should investigate the high fat effects on long-term storage and heat treatments in conjunction with in vitro digestion models. The importance of prior stress response on survival and virulence should be considered for risk analysis and in developing regulations.