Rapid Detection of Salmonella enterica from Raw and Roasted Pistachios and Almonds through Loop-Mediated Isothermal Amplification (LAMP) and Bioluminescence

Introduction: In the last decade, tree nuts have been associated with a number of Salmonella outbreaks. In the first half of 2015 in the USA, fifteen recalls, triggered by routine examination, took place due to the presence of Salmonella. Detection of foodborne pathogens in this particular commodity is challenging as microorganisms can potentially be stressed due to the low availability of both water and nutrients.  Providing methods and technologies that can offer high sensitivity and specificity to recover and rapidly detect pathogenic microorganisms from these matrices is essential.

Purpose: To assess the performance of a rapid method based on LAMP-bioluminescence to detect Salmonella enterica from raw and roasted almonds and pistachios compared to FDA/BAM as reference method.

Methods: Portions of 25 g of in-shell raw, kernel meat and roasted pistachios and almonds were inoculated with 1-5 CFU of lyophilized Salmonella (n=9/nut/method/microorganism; N=108). Non-inoculated controls were also included (n=3/nut/method/microorganism; N=36). Inoculated samples and controls were enriched and processed for detection of target organisms following FDA/BAM procedures or were enriched with 225 ml of buffered peptone water ISO and incubated at 37°C/18 h followed by detection of target microorganisms with the LAMP-bioluminescence rapid method. Probability of detection (POD) was calculated to compare the two methods.

Results: The rapid method based on LAMP-bioluminescence was able to detect Salmonella from pistachios and almonds after enrichment providing next day results. No significant difference (P<0.05) was determined between the POD of the FDA/BAM and the LAMP-bioluminescence methods.

Significance: Salmonella enterica detection through LAMP-bioluminescence, a rapid technology that allows sensitive detection of foodborne pathogens from difficult matrices like nuts, offers this industry a tool to support food safety programs related to pathogen testing.