Real-Time Loop-Mediated Isothermal Amplification (LAMP) Method for Quantitative Salmonella Typhi Detection Based on ViaB Gene

 The Salmonella origin diseases is wide which could be from gastroenteritis, enteric fever, bacteraemia and focal infection. The infection of salmonella usually comes from the consumption of the contaminated food or water with animal or human excrement. This study aimed to design a Quantitative-LAMP method to real-time detection of Salmonella enterica serovar Typhi (S. Typhi), the causative agent of Typhoid fever.

A new LAMP primer set specifically was designed based on ViaB gene and used for detection of S. Typhi. To evaluate the analytical specificity, the genome of some Salmonella-related and non-related bacteria were subjected to the S. Typhi LAMP assay. Also, the analytical sensitivity or limit of detection of the assay was evaluated. Furthermore, in the experiment, turbidity in tubes was assessed by a turbidimeter and then a standard curve was depicted by plotting time threshold values against the log of ViaB gene copy number. With this standard curve, we could use the method to make a quantitative.

The Salmonella Typhi LAMP assay specifically assessed the ViaB gene. The analytical sensitivity of the assay when using agarose gel electrophoresis or amplification plot obtained from Loop amp real-time turbidimeter system was 0.28 fg whereas with direct observation of fluorescent color change to evaluate amplification was 2.8 fg. So, the lower limit of detection of the assay when applying the revealing methods was ~1 and 8 copies of the ViaB gene respectively. 

The Salmonella Typhi LAMP assay is a simple and accurate tool to detect the causative agent of Typhoid fever that may designate to apply in clinical laboratories