P1-84 Presence and Levels of Salmonella on Raw California Pistachios

Sunday, July 26, 2015
Exhibit Hall (Oregon Convention Center)
Vanessa Lieberman, University of California, Davis, CA
Mai Yang, Dried Fruit Association of California, Fresno, CA
Thomas Jones, Dried Fruit Association of California, Fresno, CA
Edward Atwill, University of California, Davis, CA
Linda J. Harris, University of California, Davis, CA
Introduction: Little is known about the prevalence, levels, and distribution of Salmonella in most tree nuts. Such data are important in developing quantitative microbial risk assessments and scientifically-sound product sampling schemes for verification of food safety plans.

Purpose: The objective of this study was to determine the prevalence, levels, and distribution of Salmonella in raw California pistachios.

Methods: Pistachio samples were collected over 3 years from storage silos located at seven pistachio handlers representing ~98% of California production. Samples were divided between nuts from the sinker and floater streams (typically representing 85% and 15%, respectively, of the total harvest). Samples were stored at 4°C prior to enriching 100-g subsamples for the presence of Salmonella. Levels of Salmonella in positive samples were determined using a most-probable-number (MPN) method. Isolates were serotyped, phage typed when appropriate, and PFGE patterns were determined.

Results: Thirty-two of 3,968 100-g samples of pistachios (0.81%) were positive for Salmonella: 11 of 1,152 (1.0%), 6 of 1,380 (0.43%) and 15 of 1,436 (1.0%) in 2010, 2011, and 2012, respectively. The average prevalence in sinkers and floaters was 0.37% (11/2,936; range 0.10–0.71%) and 2.0% (21/1,032; range 0.63–3.7%), respectively. In every sinker sample levels of Salmonella were 0.0046 MPN/g [95% Confidence Limits (CL) 0.00064, 0.034 MPN/g]; the geometric mean level in floater pistachios was 0.012 MPN/g (range 0.0046 [95% CL 0.00064, 0.034 MPN/g] to 0.43 [95% CL 0.10, 1.8 MPN/g]). The 63 Salmonella isolates were serotyped as follows: Enteritidis (6; phage type 9c (3), 37 (1) and routine dilution non conformity (3)), Montevideo (31), Liverpool (9), Senftenberg (8), Tennessee (1), and Worthington (8). One (Tennessee and Worthington) or three (Enteritidis, Liverpool, Montevideo, and Senftenberg) PFGE patterns were identified within each serovar; most PFGE patterns were observed in more than 1 year of pistachio sampling. 

Significance: Salmonella can be isolated from raw pistachios at low prevalence and levels, with distinct differences between sinker and floater streams.