Preparation And Detection Of Food Microbiology Proficiency Testing Samples

In this study we used Salmonella, EHEC O157, EPEC O111 as the research object, to prepare the Proficiency Testing samples of three pathogens. The samples were cultured and detected, the homogeneity and stability test were performed, to make sure that the PT samples prepared were homogeneous, stable and qualified, aslo to evaluate participating laboratories’ detection ability.Each project should prepare positive and negative PT samples which included target bacteria and interference bacteria. Both strains need to be identified. Then the broth of strains were serially diluted with distilled water and all colonies were counted to study the adding concentration. Freeze-dried mung bean powder was selected as matrix, and samples were prepared and stored by vacuum freeze-drying method. The random selected samples were detected and homogeneity and stability test were performed with them. When the detection was qualified, assigned the prepared samples to participating laboratories. Each sample finally contained about 10~100 cfu/mL bacteria and 104cfu/mL interference whose biochemical properties were similar with the target bacteria, Skimmed milk powder was used as lyoprotectant to store samples, The random selected samples could be effectively identified through a variety of detection techniques, the qualified rate was 100%, and the homogeneity and stability test results showed that prepared PT samples had great homogeneity and stability.The study established a systematic procedure about the preparation and evaluation of Proficiency Testing samples for Salmonella, EHEC O157, EPEC O111. PT samples for Salmonella, E.coli O157 and E.coli O111 were successfully prepared through detection,identification and homogeneity and stability test.