Loop-Mediated Isothermal Amplification for Salmonella Detection in Food and Feed: Current Applications and Future Directions

Abstract

Loop-mediated isothermal amplification (LAMP) has become a powerful alternative to polymerase chain reaction (PCR) for pathogen detection in clinical specimens and food matrices. Nontyphoidal Salmonella is a zoonotic pathogen of significant food and feed safety concern worldwide. The first study employing LAMP for the rapid detection of Salmonella was reported in 2005, 5 years after the invention of the LAMP technology in Japan. This review provides an overview of international efforts in the past decade on the development and application of Salmonella LAMP assays in a wide array of food and feed matrices. Recent progress in assay design, platform development, commercial application, and method validation is reviewed. Future perspectives toward more practical and wider applications of Salmonella LAMP assays in food and feed testing are discussed.

Keywords: LAMP; Salmonella; detection; feed; food.

FIG. 1.

LAMP commercial applications. (a) Loopamp Realtime Turbidimeter LA-500 and reagent kits (Eiken Chemical Co., Ltd., Tokyo, Japan); (b) illumipro-10 and illumigene Molecular Diagnostic System (Meridian Bioscience, Inc., Cincinnati, OH); (c) ESEQuant TS2 (Qiagen, Venlo, Netherlands); (d) RTisochip-A (CapitalBio Technology Co., Ltd., Beijing, China); (e) Genie II and reagents (OptiGene Ltd., West Sussex, United Kingdom); (f) PDQ (ERBA Molecular, Cambridgeshire, United Kingdom); (g) 3M Molecular Detection System and assays (3M Food Safety, St. Paul, MN); (h) HumaLoop T and assays (HUMAN Diagnostics, Wiesbaden, Germany). LAMP, loop-mediated isothermal amplification.

FIG. 2.

A sequence alignment to illustrate the positions of six LAMP primers (F3, B3, FIP, BIP, LF, and LB) on the target gene. Partial nucleotide sequence of the Salmonella invasion gene invA (GenBank accession No. M90846) is shown, which was the target gene used to design our Salmonella LAMP assay (Yang et al., 2016). F3 and B3 are the forward and backward outer primers, respectively. FIP/BIP consists of complementary sequences of F1c/B1c and F2/B2 regions. BIP, backward inner primer; FIP, forward inner primer; LAMP, loop-mediated isothermal amplification; LB, loop backward; LF, loop forward.

FIG. 3.

Monitoring methods used to detect LAMP amplicons. (a) Naked eye observation based on white precipitate (Hara-Kudo et al., 2005), DNA dye (SYBR Green I) (Mashooq et al., 2016), and colorimetric indictor (calcein) (Li et al., 2016), respectively; (b) gel electrophoresis (Hara-Kudo et al., 2005); (c) real-time turbidity (Domesle et al., 2018); (d) real-time fluorescence (Domesle et al., 2018); (e) BART (Yang et al., 2016); (f) ELISA (Ravan and Yazdanparast, 2012); (g) LFD (Zhao et al., 2017); and (h) electrochemical method (Hsieh et al., 2012). BART, bioluminescent assay in real-time; ELISA, enzyme-linked immunosorbent assay; LAMP, loop-mediated isothermal amplification; LFD, lateral flow dipstick. Figure reprinted from Hsieh K, et al. 2012, Angewandte Chemie International Edition. Reproduced by permission of John Wiley & Sons, Inc.

FIG. 4.

Microfluidic devices designed for LAMP-based detection of Salmonella. (a) MEQ-LAMP (Hsieh et al., 2012); (b) eight-chamber LOC with integrated sample preparation (Sun et al., 2015); (c) iD-LAMP (Santiago-Felipe et al., 2016); (d) integrated rotary microfluidic LAMP (Park et al., 2017); (e) centrifugal microfluidic LAMP (Sayad et al., 2018); and (f) hand-powered centrifugal microfluidic LAMP (Zhang et al., 2018). Figure reprinted in part from Hsieh K, et al. 2012, Angewandte Chemie International Edition. Reproduced with permission of John Wiley & Sons, Inc; and Sun Y, et al. 2015 and Zhang L, et al. 2018. Lab on a Chip. Reproduced with permission of The Royal Society of Chemistry. iD-LAMP, in-disc LAMP; LAMP, loop-mediated isothermal amplification; LOC, lab-on-a-chip; MEQ, microfluidic electrochemical quantitative.