Acidification and extended storage at room temperature of mayonnaise reduce Salmonella Typhimurium virulence and viability

• Published in: Food research international 2021-03, Vol.141, p.110117-110117, Article 110117
• Main Authors: McWhorter, Andrea R., Khan, Samiullah, Sexton, Margaret, Moyle, Talia S., Chousalkar, Kapil K.
• Format: Article
• Language: English
• Subjects: Acidification; BALB/c mice; Invasion; Raw egg sauces; Salmonella Typhimurium; Virulence
• ISSN: 0963-9969; 1873-7145
• DOI: 10.1016/j.foodres.2021.110117

[Display omitted] •S. Typhimurium culturability is reduced in acidified mayonnaise and is affected by temperature.•Bacterial motility and invasive ability are inhibited in acidified mayonnaise.•S. Typhimuiurm in acidified mayonnaise preparations exhibited reduced disease capacity in mice.•S. Typhimurium in acidified mayonnaise exhibited reduced ATP production over time. Despite food safety recommendations, raw egg-based foods, such as mayonnaise, are frequently identified as the source of Salmonella during outbreaks. Acidification and storage temperature have been linked with reduced bacterial culturability. Raw egg-based sauces stored at 25 °C have historically been linked with faster decline of Salmonella culturability than preparations stored at 5 °C. This study aimed to determine whether reduced culturability in acidified mayonnaise correlated with reduced in vitro bacterial motility, invasiveness and viability as well as disease-causing capacity in BALB/c mice. Acidification of mayonnaise and incubation at 25 °C for 4 h significantly reduced culturability of Salmonella Typhimurium DT9 but was dependent on initial bacterial load. Bacteria recovered from acidified mayonnaise exhibited reduced invasiveness into polarized cultured intestinal epithelial cells and 12 h post inoculation were no longer invasive suggesting a reduced capacity to cause disease. To confirm this, BALB/c mice were inoculated with Salmonella Typhimurium contaminated mayonnaise stored at 5 °C or 25 °C for 12, 24, 48, 72, and 96 h. Mice inoculated with mayonnaise incubated at 5 °C for 12 and 24 h exhibited mild to moderate disease symptoms; all other mayonnaise treatment groups did not exhibit disease symptoms. In acidified mayonnaise, Salmonella Typhimurium DT9 exhibited a global downregulation of metabolism, stress response, and virulence genes upon addition to mayonnaise. After 4 h of incubation at both 5 °C and 25 °C, however, the vast majority of genes were upregulated which was maintained over the 96-hour experiment suggesting that bacteria were severely stressed. Salmonella Typhimurium DT9 cells were isolated from mayonnaise samples and ATP production was quantified. At both 5 °C and 25 °C, ATP production decreased in acidified mayonnaise preparations. At 25 °C, ATP production decreased more rapidly than at 5 °C. After 24 h, ATP production of bacteria in mayonnaise stored at 25 °C was not significantly different from the dead control group. Thus, the current recommendation of o