Microbiology Methods for ERP Review 3-2020

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Preparation of Inoculum and Test Portions

The Salmonella strain used in this evaluation was rehydrated from lyophilized pellets (BIOBALL ® , bioMérieux, #413775) into 10 mL buffered peptone water. Once rehydrated, the culture was homogenized thoroughly and dilutions (1:10) were prepared in Butterfield’s phosphate buffered diluent (BPD) for both the low and high inoculation levels. A bulk lot of matrix was inoculated with 10 mL of culture for each contamination level, homogenized by hand mixing and packaged into individual test portions for the GENE-UP SLM method or reference method. For the GENE-UP SLM test portions, 25 g of inoculated test material was combined with 350 g of non-inoculated test material. Reference method test portions were 25 g.

Test Portion Distribution

Samples were blind-coded and shipped to the collaborating sites at refrigerated temperature (2-8°C). Samples were received on a Friday and held at 2-8 o C until analysis was initiated the following Monday. Within each shipment, a sample labeled temperature control was included. Participants were instructed to report the temperature of the samples on the sample receipt form and return to the study directors. Temperature records for each laboratory have been included with the supplementary materials.

Test Portion Analysis

Test portions (375 g) evaluated by the candidate method were enriched with 1125 mL of BPW (prewarmed to 42 ± 1 o C), homogenized for 2 min and incubated for 10 h at 42 ± 1°C.

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