Application of loop-mediated isothermal amplification to detect Salmonella spp. in egg samples

Abstract

The objective of the study was to evaluate the use of loop-mediated isothermal amplification (LAMP) technique for detection of Salmonella spp. in chicken eggs. Eight Salmonella strains and 26 non-Salmonella enteric strains were used to verify the specificity of the LAMP assay for detection of Salmonella. The Sal4 primer set was used to specifically amplify the target sequence on the invA gene of Salmonella and the hydroxyl naphthol blue was used as the indicator to read the reaction results. Blank egg samples were spiked with serial 10-fold diluted Salmonella suspensions to determine the limit of detection at 50% (LOD50) of the assay. Egg samples collected from multiple locations in Ho Chi Minh City were tested for the presence of Salmonella using both LAMP method and the traditional culture method to compare the effectiveness of these two methods. Among 34 bacterial strains tested by LAMP assay, false-positive or false-negative results were not observed. The assays of spiked egg samples showed that the LOD50 of the LAMP method was less than 2 CFU/25 g sample. These results indicated a high specificity and sensitivity of the LAMP assay in detection of Salmonella in egg samples, even with those of low levels of contamination. Upon testing collected egg samples (n = 42), the LAMP assay produced the same results of Salmonella detection as the culture method. Salmonella was detected in 4 out of 42 samples. This study showed that the LAMP method is highly effective and would be suitable for use in detection of Salmonella in egg samples. The assay has several advantages such as saving time and labor compared to traditional culture methods.