Comparative Study between 3M™ Petrifilm™ Salmonella Express System and Reference Method ISO 6579 for Salmonella Species Detection in Thai Fruit and Vegetable Products and Seasoning

Introduction: Salmonella spp. are important pathogens implicated in the contamination of fruit, vegetable and seasoning products. Rapid and convenient detection of Salmonella helps food processors make fast, informed decisions.

Purpose: This study aimed to compare the 3M^TM Petrifilm^TM Salmonella Express System with a reference method (ISO 6579) for the detection of Salmonella spp. in fruit, vegetable and seasoning products from Thailand.

Methods: A total of 116 samples were tested with both methods. Samples were spiked with 5 serovars of Salmonella spp. (Anatum, Weltevreden, Stanley, Rissen and Typhimurium) at low (1–50 CFU/25 g), medium (>50 - 600 CFU/25 g) and high (>600 - 40,000 CFU/25 g) levels. These serovars represent the most frequently detected contaminants in food products analyzed by the Regional Medical Sciences Center 1, Chiang Mai. Twenty-five grams of each spiked sample was homogenized, divided and analyzed by 3M^TM Petrifilm^TM Salmonella Express System and ISO 6579. Six replicates of 2.0 CFU/25 g, 4.0 CFU/25 g and 8.0 CFU/25 g contamination levels in frozen green soybean were analyzed by 3M^TM Petrifilm^TM Salmonella Express System for LOD₅₀ detection.

Results: 3M^TM Petrifilm^TM Salmonella Express System results revealed 100% sensitivity, 100% accuracy and 100% specificity. The six replicates analysis showed 1/6, 3/6 and 6/6 positive results for 2.0 CFU/25 g, 4.0 CFU/25 g and 8.0 CFU/25 g contamination levels, respectively. The limit of detection (LOD₅₀) using Spearman-Karber method (Excelpros 20) showed approximately 7 (or 6.55) CFU/25 g.

Significance: 3M^TM Petrifilm^TM Salmonella Express System is a rapid method with high efficacy, high accuracy, and is less time consuming than standard agar methods. The LOD₅₀ in food samples gave acceptable results in this study.