Category Archives: Research

Journal of Food Protection

The use of high-throughput methods allows a better characterization of food-related bacterial communities. However, such methods require large amounts of high quality bacterial DNA, which may be a challenge when dealing with a complex matrix that has a low concentration of bacteria like fresh fish fillets. Therefore, the choice of method used to recover bacteria from a food matrix in a cost-effective way is critical, yet little information is available on the performance of commonly used methods. We assessed the recovery capacity of two such methods: stomaching and mechanical rinsing. The efficiency of the methods was evaluated through the quantitative recovery and compatibility with end-point qPCR. Fresh rainbow trout ( Oncorhynchus mykiss ) fillets were inoculated with a bacterial marker, Brochothrix thermosphacta , at different concentrations (7.52 to 1.52 log CFU/g). The fillets were processed by one of the two methods and the recovery of the marker in the suspensions was assessed by plate counting and qPCR targeting B. thermosphacta – rpoC . The same analyses were performed on 6 non-inoculated fresh fillets. Stomaching and mechanical rinsing allowed an efficient and repeatable recovery of the bacterial communities from the 42 inoculated fillets. No significant differences of Recovery Ratios were observed between the marker enumerated in the inoculation suspensions and in the corresponding recovery suspensions after rinsing and stomaching. However, the stomaching method allowed too many particles to pass through the filters bag, making necessary a limiting supplementary filtration step. As a consequence, only the rinsing recovery method allowed a proper PCR quantification of the inoculated B. thermosphacta. The mean recovered bacterial level of the fillets was around 3 log CFU/g. It seems more relevant and cost-effective to recover the endogenous bacterial microbiota of a fish fillet structure using the rinsing method rather than the stomaching method.