Independent laboratory validation of a Salmonella loop-mediated isothermal amplification assay in 27 human and animal food matrices of 9 ISO food categories

Abstract

Improvement in Salmonella screening methods greatly enhances the efficiency of food safety testing programs. This study aimed at extending a Salmonella loop-mediated isothermal amplification (LAMP) assay initially validated in animal food to 27 additional human and animal food matrices through the U.S. Food and Drug Administration (FDA)'s Laboratory Flexible Funding Model (LFFM) collaboration with state agricultural and public health laboratories. These matrices represented nine International Organization for Standardization (ISO) food categories: chocolate, bakery products and confectionary; dried cereals, fruits, nuts, seeds and vegetables; eggs and egg products; environmental samples; fish and seafoods; fresh produce and fruits; infant formula and infant cereals; milk and dairy products; and pet food and animal feed. For each matrix, one of the LFFM laboratories received 30 blinded test portions spiked with low (fractional) or high levels of Salmonella and uninoculated controls. All test portions were processed for Salmonella isolation, according to the FDA's Bacteriological Analytical Manual (BAM) Chapter 5. Overnight enrichments were also screened by LAMP (on one of two platforms). Aerobic plate counts and most probable numbers were obtained for all matrix sets except two environmental surfaces sampled with sponges or swabs. All of the 27 matrices were successfully validated by these independent laboratories as evidenced by clean uninoculated controls (all negative), fractional recoveries (25-75 %), and acceptable relative level of detection (RLOD) values (below 1.5 for a paired study). Extension of the validation of this rapid, reliable, and robust Salmonella LAMP screening method to nine ISO food categories consisting of various human and animal food matrices greatly streamlines the laboratory workflow, which will have a far-reaching impact on food safety and public health once the method is widely adopted.

Keywords: Animal food; Human food; LAMP; Matrix; Salmonella; Screening; Validation.