Detection of Salmonella Spp. in Egg Laying Hens Collected from Poultry Facilities in Batangas, Philippines using Culture-Based Diadnostic Assay and Loop-Mediated Isothermal Amplification (Lamp) Method

Abstract

Salmonella spp. are foodborne pathogens known to cause numerous outbreaks and is considered to be one of the top 4 causes of foodborne illnesses in the Philippines. It is transmitted through the fecal-oral route and poultry including live chickens, meat, and eggs are the common sources of contamination. The need for a rapid and accurate detection methods to minimize food safety risks and the spread of this food pathogen is therefore essential. This study compared the accuracies of two diagnostic methods, culture based and loop-mediated isothermal amplification (LAMP) assay in culture detection of Salmonella from poultry samples. Salmonella spp. were collected through cloacal swabs from egg laying hens from various poultry farms in Batangas, Philippines. A total of 50 samples were enriched in Rappaport Vassiliadis (RV) broth overnight at 42 oC and plated onto Xylose Lysine Deoxycholate (XLD) agar. Results showed that out of 50 samples, 42 (84%) exhibited growth on XLD agar. However, none of the isolates exhibited formation of black colonies indicative of Salmonella growth. The genomic DNA was then extracted and used as template for the LAMP assay using a detection kit currently being developed by a private company. The genomic DNA was successfully extracted from 40 out of the 50 (80%) samples grown on RV broth. When tested for the LAMP assay, only 2 out of 40 (5.0%) samples were positive based on fluorescence but both samples were not detected by the culture method. Furthermore, the positive control of S. Typhimurium ATCC 13311 strain which was positive by the culture method was also not detected by the LAMP assay. This present study therefore showed that the results of the LAMP assay gave false positives compared to the culture method. Moreover, a false negative was also observed as the positive control S. Typhimurium ATCC 13311 did not fluoresce when subjected to the LAMP assay. Further optimization of the specificity of the LAMP kit is recommended. Sampling methods may also be modified for Salmonella isolation in the next diagnostic trials.