Purpose: The aim of this study is to determine natural contamination rates of Salmonella in cook-chill and cook-freeze foods sold in Bangkok. Additionally, this study aims to evaluate the performance of 3M™ Petrifilm™ Salmonella Express (SALX) System for the detection of Salmonella spp. in various types of cook-chill and cook-freeze foods compared to the standard ISO 6579 conventional method
Methods: Cook-chill (26 samples) and cook-freeze (74 samples) foods were randomly purchased from supermarkets in Bangkok. Fifty grams of each sample was homogenized, divided equally and analyzed following two methods: (1) 3M™ Petrifilm™ SALX System; (2) ISO 6579 using BPW pre-enrichment, MKTTn & RV selective enrichment, and XLD & HE agar for selective plating. Furthermore, five replicates of six different matrices (Salmonella negative samples, n = 30) were spiked with low levels (1–10 CFU/25g) of Salmonella Typhimurium to validate the performance of 3M™ Petrifilm™ SALX System compared to the standard ISO 6579 conventional method.
Results: Nine samples (8.22%) of cook-freeze foods were naturally contaminated with Salmonella spp. (five samples were positive by both methods; three samples were positive by ISO method only; one sample was positive by 3M™ Petrifilm™ SALX System only). All cook-chill samples were negative (0% natural contamination). For the artificially inoculated samples the relative accuracy, relative sensitivity and relative specificity of the 3M™ Petrifilm™ SALX System was found to be 96.9%, 92.1% and 98.9%, respectively.
Significance: The data from this study supports the use of 3M™ Petrifilm™ SALX System as a rapid and cost-effective method for Salmonella detection in cook-chill and cook-freeze foods.