title: Evaluation of loop-mediated isothermal amplification for the rapid, reliable, and robust detection of Salmonella in produce.
abstract: Rapid, reliable, and robust detection of Salmonella in produce remains a challenge. In this study, loop-mediated isothermal amplification (LAMP) was comprehensively evaluated against real-time quantitative PCR (qPCR) for detecting diverse Salmonella serovars in various produce items (cantaloupe, pepper, and several varieties of lettuce, sprouts, and tomato). To mimic real-world contamination events, produce samples were surface-inoculated with low concentrations (1.1-2.9 CFU/25 g) of individual Salmonella strains representing ten serovars and tested after aging at 4 °C for 48 h. Four DNA extraction methods were also compared using produce enrichment broths. False-positive or false-negative results were not observed among 178 strains (151 Salmonella and 27 non-Salmonella) used to evaluate assay specificity. The detection limits for LAMP were 1.8-4 CFU per reaction in pure culture and 10(4)-10(6) CFU per 25 g (i.e., 10(2)-10(4) CFU per g) in produce without enrichment, comparable to those obtained by qPCR. After 6-8 h of enrichment, both LAMP and qPCR consistently detected these low concentrations of Salmonella of diverse serovars in all produce items except sprouts. The PrepMan Ultra sample preparation reagent yielded the best results among the four DNA extraction methods. Upon further validation, LAMP may be a valuable tool for routine Salmonella testing in produce. The difficulty of detecting Salmonella in sprouts, whether using LAMP or qPCR, warrants further study.
authors.affiliation: Division of Animal and Food Microbiology, Office of Research, Center for Veterinary Medicine, U.S. Food and Drug Administration, Laurel, MD 20708, USA; Department of Food Science, Louisiana State University Agricultural Center, Baton Rouge, LA 70803, USA.
authors.forename: Qianru
authors.initials: Q
authors.lastname: Yang
authors.affiliation: Division of Animal and Food Microbiology, Office of Research, Center for Veterinary Medicine, U.S. Food and Drug Administration, Laurel, MD 20708, USA; Department of Nutrition and Food Science, University of Maryland, College Park, MD 20742, USA.
authors.forename: Fei
authors.initials: F
authors.lastname: Wang
authors.affiliation: Division of Animal and Food Microbiology, Office of Research, Center for Veterinary Medicine, U.S. Food and Drug Administration, Laurel, MD 20708, USA.
authors.forename: Kelly L
authors.initials: KL
authors.lastname: Jones
authors.affiliation: Department of Nutrition and Food Science, University of Maryland, College Park, MD 20742, USA.
authors.forename: Jianghong
authors.initials: J
authors.lastname: Meng
authors.affiliation: Department of Food Science, Louisiana State University Agricultural Center, Baton Rouge, LA 70803, USA.
authors.forename: Witoon
authors.initials: W
authors.lastname: Prinyawiwatkul
authors.affiliation: Division of Animal and Food Microbiology, Office of Research, Center for Veterinary Medicine, U.S. Food and Drug Administration, Laurel, MD 20708, USA. Electronic address: beilei.ge@fda.hhs.gov.
authors.forename: Beilei
authors.initials: B
authors.lastname: Ge
mesh_terms: D000818:Animals; D015373:Bacterial Typing Techniques / Q000379:methods*; D005516:Food Microbiology; D006801:Humans; D021141:Nucleic Acid Amplification Techniques / Q000379:methods*; D010944:Plants / Q000382:microbiology; D012475:Salmonella / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*; D012480:Salmonella Infections / Q000382:microbiology; D012680:Sensitivity and Specificity; D014675:Vegetables / Q000382:microbiology*
keywords: Detection; LAMP; Produce; Salmonella; qPCR