Poster Presentation Australian Society for Microbiology Annual Scientific Meeting 2018

Exploring the behaviour of Salmonella Typhimurium in aioli, a raw egg-based sauce (#328)

Andrea R. McWhorter 1 , Talia S Moyle 1 , Kapil K Chousalkar 1
  1. University of Adelaide, Roseworthy, SA, Australia

Salmonella spp. remains one of the most common causes of foodborne gastrointestinal disease. Raw or undercooked eggs or food items containing raw eggs are commonly identified as sources of Salmonella. Based on previous research, acidification and cold storage are utilised to prevent bacterial growth and limit survival, yet Salmonella is often isolated from mayonnaise and aioli during trace back investigations. In the present study, the effect of temperature and pH on the culturability of Salmonella Typhimurium in freshly prepared aioli was investigated. Bacteria were grown overnight either in Luria Bertani or minimal M9 media and diluted to a concentration of 105 CFU/ gram aioli prepared at pH 3.5, 4.0, 4.5, or 5.0. Samples were incubated at 5°C and 25°C and bacteria were tested at 0, 4, 8, 12, 24, 48, 72, and 96 hours post-inoculation. At 5°C, the total amount of culturable Salmonella in aioli pH 3.5 and 4.0 decreased between 4 and 8 hours post inoculation, with no bacteria cultured subsequently. At higher pH (4.5 and 5.0), Salmonella was cultured until 72 hours. At 25°C, Salmonella was not cultured at any time point from aioli pH 3.5 or 4.0; at pH 4.5 and 5.0, however, bacteria were cultured at 4 and 8 hours. Increasing the inoculum (109 CFU/gram pH 3.5) extended the culturability time at both 5°C and 25°C. Bacteria grown in non-nutritive M9 media exhibited a similar pattern at both temperatures. The bactericidal effects of lemon juice and vinegar were also investigated. Different ratios of lemon juice and vinegar were used to create aioli pH 3.5 but no effect on culturability of Salmonella was observed. Live/dead staining on aioli preparations where bacteria were no longer culturable revealed that the majority of the bacteria were alive. Aspects of bacterial virulence, including motility and invasiveness into cultured intestinal epithelial cells are currently being investigated.