P3-80 Survival of Salmonella, Escherichia coli O157:H7 and Listeria monocytogenes on Pecans and Peanuts and Characterization of Salmonella Isolates

Wednesday, July 31, 2013
Exhibit Hall (Charlotte Convention Center)
Pardeepinder Brar, University of Florida, Lake Alfred, FL
Lisseth Proano, University of Florida, Lake Alfred, FL
Loretta Friedrich, University of Florida, Lake Alfred, FL
Linda Harris, University of California-Davis, Davis, CA
Michelle Danyluk, University of Florida, Lake Alfred, FL
Introduction: Outbreaks due to Salmonella and Escherichia coli O157:H7 and recalls associated with these organisms and Listeria monocytogenes are documented for the consumption of nuts

Purpose: Our objective was to evaluate the fate of Salmonella, E. coli O157:H7 and L. monocytogenes on pecans and peanuts stored at -20, 4 and 23°C for up to 12 months, and to characterize Salmonella isolates remaining after 18 months of storage.

Methods: Raw pecans and peanuts were inoculated with cocktails of nalidixic acid-resistant strains of Salmonella, E. coli O157:H7 and L. monocytogenes, dried for 72 h, and stored at -20, 4, 23°C for 18 months. Microbial populations were enumerated over 12 months by stomaching 10-g subsamples and plating onto specific and non-specific media supplemented with nalidixic acid. After 18 months, 100 Salmonella colonies isolated from each storage temperature were characterized to determine the prevalence of each cocktail strain by a combination of serogrouping, antibiotic resistance, and PCR for strain-specific genes.

Results: At 23ºC, Salmonella, E. coli O157:H7 and L. monocytogenes declined linearly at rates of -0.20, -0.33, -0.54 log CFU/g/month on peanuts and -0.16, -0.33, -1.05 log CFU/g/month on pecans, respectively. At 4°C, population of Salmonella declined on peanuts at -0.039 log CFU/g/month and remained relatively stable on pecans. E. coli O157:H7 and L. monocytogenes populations remained stable at 4ºC storage on both nut types. At -20ºC, populations of the three pathogens remained stable on both nuts with the exception of L. monocytogenes which declined at -0.06 log CFU/g/month on peanuts. Salmonella Tennessee predominated on peanuts and pecans -20, 4 and 23°C, except on peanuts stored at 23°C storage where Salmonella Enteritidis 9C was predominantly isolated.

Significance: Pathogens, if present, can survive for extended periods of time at a broad range of storage temperatures on raw pecans and peanuts. Storage under refrigerated or freezing temperatures does not result in pathogen reduction.