AOAC RI ERP Final Action Recommendations eBook

Dupont BAX Salmonella PTM Report Modification Approved 2012 / PTM Certification No. 081201 For Expert Review Panel Use Only Do Not Distribute

15. INCLUSIVITY EXCLUSIVITY STUDY

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Sample Preparation and Enrichment

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For inclusivity testing, 62 different Salmonella strains representing more than 50 serotypes

were selected from the DuPont Qualicon Culture Collection. These strains originated from a

wide range of food, environmental, human and veterinary clinical diagnostic and animal non-

diagnostic samples. Cultures were streaked for purity on BHI agar, then one pure colony was

inoculated into BPW and incubated at 41°C overnight to reach cell densities of approximately

10 9 cfu/ mL. Enrichments were serially diluted to approximately 10 5 cfu/mL before testing, which

is 1 log over the claimed sensitivity of the assay.

For exclusivity testing, 35 different non- Salmonella strains were selected from the DuPont

Qualicon Culture Collection. Most of these isolates were selected based upon genetic

relatedness to Salmonella and originally obtained from naturally contaminated food and food

processing environmental samples or from animal sources, and all identifications were

confirmed biochemically and/or serologically as appropriate. Exclusivity cultures were primarily

selected based upon genetic relatedness to Salmonella. Cultures were streaked for purity on

BHI agar, then one pure colony was inoculated into a tube containing BHI broth and incubated at

35ºC overnight to reach cell densities of approximately 10 9 cfu/ mL. For exclusivity testing,

cultures were tested with no dilution.

All inclusivity and exclusivity strains were tested with the updated BAX® System method as

described above.

AOAC INTERNATIONAL Results The results of inclusivity testing are displayed in Table 4 below. The updated BAX® System method returned positive results for all 62 Salmonella strains tested. Compared to the current

certified method, which missed one strain, Salmonella Westmark II (DD1560), at 10 5 cfu/mL in

the original validation study, the updated method shows slightly increased sensitivity and now

reliably detects this strain at 10 5 cfu/mL.