Comparative Detection of Salmonella in Philippine Desiccated Coconut Using 3MTM Molecular Detection Assay Salmonella, 3MTM PetrifilmTM Salmonella Express System, and Bismuth Sulphite Agar

Introduction: Salmonella spp. is an important foodborne pathogen worldwide, considered as a leading cause of food poisoning. Recently, there have been cases of Philippine desiccated coconut being confirmed positive for the presence of Salmonella, which were only detected when the products were already in the importing countries.

Purpose: The study aimed to compare sensitivity and selectivity of three Salmonella methods: 3M Molecular Detection Assay Salmonella; 3M Petrifilm Salmonella Express System; and spread plating on bismuth sulphite agar (BSA).

Methods: For the sensitivity assay, desiccated coconut samples were decontaminated at 121°C for 20 minutes and spray inoculated with decreasing levels of Salmonella enterica serovar Typhimurium (ATCC 14028) ranging from ca. 1 to 5 log CFU/g. Selectivity testing was conducted using decontaminated desiccated coconut samples inoculated with the following mixtures: Salmonella + Escherichia coli O157:H7, Salmonella + Listeria monocytogenes, Salmonella + methicillin-resistant Staphylococcus aureus (MRSA), and Salmonella + E. coli O157:H7 + L. monocytogenes+ MRSA. All samples were then subjected to three detection methods. 

Results: The 3M Molecular Detection Assay Salmonella and 3M Petrifilm Salmonella Express System were able to detect Salmonella at levels as low as 1.6 log CFU/g (39 cells/g) while direct plating on bismuth sulphite agar detected as low as 2.6 log CFU/g (398 cells/g). The detection of Salmonella in all three methods was not hampered by the presence of any non-Salmonella microorganism tested in this study.

Significance: These data suggest that the 3M Molecular Detection Assay Salmonella and 3M Petrifilm Salmonella Express System may be used as rapid detection methods for Salmonella in desiccated coconut products.