Affiliation:
1. Department of Food Science, Louisiana State University Agricultural Center, Baton Rouge, Louisiana 70803
2. Southern Regional Research Center, Agricultural Research Service, United States Department of Agriculture, New Orleans, Louisiana 70124
Abstract
ABSTRACT
Recent outbreaks linked to
Salmonella
-contaminated produce heightened the need to develop simple, rapid, and accurate detection methods, particularly those capable of determining cell viability. In this study, we examined a novel strategy for the rapid detection and quantification of viable salmonellae in produce by coupling a simple propidium monoazide sample treatment with loop-mediated isothermal amplification (PMA-LAMP). We first designed and optimized a LAMP assay targeting
Salmonella
. Second, the performance of PMA-LAMP for detecting and quantifying viable salmonellae was determined. Finally, the assay was evaluated in experimentally contaminated produce items (cantaloupe, spinach, and tomato). Under the optimized condition, PMA-LAMP consistently gave negative results for heat-killed
Salmonella
cells with concentrations up to 10
8
CFU/ml (or CFU/g in produce). The detection limits of PMA-LAMP were 3.4 to 34 viable
Salmonella
cells in pure culture and 6.1 × 10
3
to 6.1 × 10
4
CFU/g in spiked produce samples. In comparison, PMA-PCR was up to 100-fold less sensitive. The correlation between LAMP time threshold (
T
T
) values and viable
Salmonella
cell numbers was high (
R
2
= 0.949 to 0.993), with a quantification range (10
2
to 10
5
CFU/reaction in pure culture and 10
4
to 10
7
CFU/g in produce) comparable to that of PMA in combination with quantitative real-time PCR (PMA-qPCR). The complete PMA-LAMP assay took about 3 h to complete when testing produce samples. In conclusion, this rapid, accurate, and simple method to detect and quantify viable
Salmonella
cells in produce may present a useful tool for the produce industry to better control potential microbial hazards in produce.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
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