Microbiology Methods for ERP Review 3-2020

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will be used to determine the MPN values and 95% confidence intervals. The MPN is reported as 1 MPN/test portion with 95% confidence intervals.

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Table 1. Matrix Preparation

Test Portions/ Method

Test Portion Codes Random number 100 ‐ 800

Inoculation Organism

Reference Method FDA BAM Ch. 5

Matrix

Target Levels

0 CFU/test portion 0.2–2 CFU/ test portion 5–10 CFU/ test portion

12 12 12

S. Senftenberg ATCC TBD

Instant NFDM

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4.0 7 8 To prepare artificially contaminated matrix, primary test materials will be inoculated with Salmonella so 9 that on the day of initiation of analysis there is a low level (approx. 0.2–2 CFU/test portion) and a high 10 level (approximately 5–10 CFU/test portion). Note that one level of contamination must result in 11 fractional positive results. One test material will remain uninoculated to serve as the uncontaminated 12 control. The organizing laboratory will prepare and ship the test materials. Each sample will be divided 13 into test portions, randomized, and blind ‐ coded for analysis. Collaborators will complete and return the 14 data sheets to the study director following confirmation, within 2 weeks of the test initiation date. Test Material Preparation and Distribution 4.1 Instant NFDM will be obtained from a local retail outlet and screened for the presence of Salmonella . Naturally contaminated test portions will be used if available at sufficient levels. Alternatively, the test portions will be artificially contaminated to meet the 4.2 To artificially contaminate instant NFDM, a dried (lyophilized) inoculum will be used. The inoculum will be added to a bulk test material and mixed by mechanical stirring or rolling to achieve equal distribution of analyte throughout. Inoculated products will be appropriate target levels.

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stabilized for a minimum of 2 weeks at ambient temperature (20–25°C).

4.3 The 375 g test portions for the Solus One Salmonella method will be prepared by mixing

25 g of contaminated material with 350 g of uncontaminated material for each contamination level. Material will be artificially contaminated if not found to be

naturally contaminated.

4.4

Test portions will be packaged in leak ‐ proof, insulated containers and shipped (according to the Dangerous Goods Regulations IATA for Infectious Substances) by overnight carrier to arrive the day before initiation of analysis . All test portions will be shipped at ambient temperature (20–25°C). A temperature probe will be included with each shipment to verify temperature of material upon receipt. Upon arrival, the test portions will be stored at 20–25  C until they are analyzed. All participating collaborators

will begin processing and analysis on the following Monday.

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