Detecting Salmonella serovars in shell eggs by loop-mediated isothermal amplification.

Shell eggs contaminated with Salmonella Enteritidis pose serious food safety and public health concerns. More vigilant product testing calls for rapid, accurate, and reliable detection methods for Salmonella. Two loop-mediated isothermal amplification (LAMP) assays targeting different regions of the Salmonella invasion protein (encoded by invA) have been reported. In this study, performance of the two LAMP assays was compared with that of PCR in detecting Salmonella Enteritidis and Salmonella Typhimurium strains in experimentally contaminated egg homogenates. Both LAMP assays were highly specific. The detection limits were approximately 1 CFU per reaction for both Salmonella serovars in pure culture, 100-fold more sensitive than that of PCR. Standard curves generated suggested a good linear relationship between Salmonella cell numbers and LAMP turbidity signals. In spiked egg homogenate, the LAMP assays could detect both Salmonella serovars down to 10(4) CFU/25 ml without enrichment and 10(0) CFU/25 ml with 8-h enrichment. In contrast, PCR was unable to detect either Salmonella serovar in egg homogenates spiked with less than 10(6) CFU/25 ml by direct testing and required at least 12 h of enrichment for samples spiked with 10(1) CFU/25 ml and 24 h for those with 10(0) CFU/25 ml. The complete LAMP assay took about 10 h (including 8 h of enrichment) to complete. In conclusion, the two LAMP assays were rapid, accurate, and reliable methods for detecting Salmonella serovars in shell eggs and may be adopted in routine egg testing for Salmonella to improve egg safety and protect public health.