Validation of the Level 2 Modification for the Neogen® Molecular Detection Assay 2 - Salmonella Enteritidis/Salmonella Typhimurium Method for Detection of the Monophasic Variant Salmonella enterica 1,4,[5],12:-:1,2.

Background: The Neogen® Molecular Detection Assay 2-Salmonella Enteritidis/Salmonella Typhimurium (MDA2-SE/ST) method, Performance Tested Method  SM (PTM) 122302, is a nucleic acid amplification test for specific detection of Salmonella enterica ser. Enteritidis (SE) and Salmonella enterica ser. Typhimurium (ST), including the ST monophasic variant Salmonella enterica  1,4,[5],12:i:-, in select poultry samples. Results for SE and ST are generated separately.

Objective: The objective of the study was to validate the MDA2-SE/ST method for detection of an additional monophasic variant of ST, S. enterica  1,4,[5],12:-:1,2.

Methods: A single strain of S. enterica  1,4,[5],12:-:1,2 was tested as part of a seven-strain inclusivity/exclusivity test panel. Strains were tested after growth in two enrichment media used in the method, buffered peptone water (BPW) and buffered peptone water-ISO formulation (BPW-ISO), and at two incubation temperatures, 35 ± 2 °C and 41.5 ± 1 °C.

Results: S. enterica  1,4,[5],12:-:1,2 produced positive results in the ST assay and negative results in the SE assay in both enrichment media and at both incubation temperatures. Results for the other six test strains were as expected under all conditions.

Conclusions: The MDA2-SE/ST method can detect the monophasic variant S. enterica  1,4,[5],12:-:1,2 as well as S. enterica ser. Typhimurium and the monophasic variant S. enterica  1,4,[5],12:i:-. The MDA2-SE/ST method maintains inclusiveness for S. enterica ser. Typhimurium despite flagellar antigen variation.

Highlights: The data were reviewed by the AOAC PTM Program and approval was granted for modification of the MDA2-SE/ST method, PTM 122302.