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United States Department of Agriculture

Agricultural Research Service

Title: Survival of Salmonella Heidelberg in hummus

item Laycock, Andrea
item Sharma, Manan
item Kniel, Kalmia

Submitted to: Annual Meeting of the Institute of Food Technologists
Publication Type: Abstract Only
Publication Acceptance Date: 3/15/2008
Publication Date: 6/28/2008
Citation: Laycock, A., Sharma, M., Kniel, K.E. 2008. Survival of Salmonella Heidelberg in hummus. Annual Meeting of the Institute of Food Technologists., Technical Program Abstracts, p. 33

Interpretive Summary:

Technical Abstract: Salmonella Heidelberg is the fourth-most commonly reported Salmonella serotype to cause human illness. There have been several outbreaks and recalls caused by S. Heidelberg in ready to eat foods. Recently, 700 people became ill from ingesting hummus shirazi contaminated with S. Heidelberg. This study demonstrates the effects of storage conditions and acid adaptation on the behavior of S. Heidelberg in hummus. A three-strain cocktail of S. Heidelberg was grown in TSB (unadapted) or TSB supplemented with 1 percent glucose (acid-adapted) for 24 h at 37 deg C, inoculated into a commercial formulation of hummus at either a low (3 log CFU/g) or high (7 log CFU/g) population, and stored at either 4 or 22 deg C (a high inoculum of acid-adapted cells at 22 deg C were not evaluated). Populations were determined on days 0, 1, 3, 5, 8, 13, 18 and 28 on XLD media. The pH of hummus at day 0 was 4.3 and ranged from 3.8 to 5.2 throughout the study. After 28 days, unadapted and acid-adapted populations in the low and high inocula at 4 deg C remained unchanged (+1 log CFU/g). Salmonellae in the low inoculum were undetectable after 7 days while those in the high inoculum increased by 2.7 log CFU/g in hummus stored at 22 deg C. Low inocula of acid-adapted Salmonella at 22 deg C increased by 3.2 log CFU/g and decreased by 2.4 log CFU/g at 4oC. Samples with <0.5 log CFU/g at 22 deg C were enriched following FDA guidelines. In order to analyze the potential adaptation to acidic conditions, RNA from unadapted and acid-adapted cells in hummus at both temperatures was extracted and analyzed for expression of genes involved in log and stationary phase acid tolerance responses (ompR, cadC and fur). This work shows the ability of S. Heidelberg to grow in a low pH food system regardless of acid adaptation.

Last Modified: 10/17/2017
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