Thirteen isolates labeled TS (“Test study”), 8 from human cases and 5 from foods, were from the WHO international multicenter L. monocytogenes subtyping study [17, 20]. One TS strain from a human case of listeriosis was included in this study as duplicate culture (Table 1). Eleven isolates were reference strains including 8 CLIP strains and 3 fully

sequenced strains (Table 2). Table 2 Origins and serogroups of 11 L. monocytogenes reference strains used in this study Reference strains EURL Strain number Origin Molecular serogroup2 CLIP1 74902 00EB248LM Animal IIa CLIP 74903 00EB249LM Animal IIb CLIP 74904 00EB250LM Human IIc CLIP 74905 00EB251LM Human IIa CLIP 74906 00EB252LM Human IIb CLIP 74907 00EB253LM Animal IIb CLIP 74910 00EB256LM Environment see more IVb CLIP 74912 00EB258LM

Animal IVb EGDe EGDe Animal IIa (Accession LCZ696 concentration number: AL591824)   [21]       F2365 F2365 Food IVb (Accession number: AE017262)   [22]       CLIP80459 [23] CLIP80459 Human IVb 1 CLIP: Pasteur Institute collection. 2 Serogrouping performed by multiplex PCR [4]: results are from both the European Reference Laboratory (EURL) for L. monocytogenes and the UK National Reference laboratory (UK-NRL) for Listeria. Molecular serogrouping All the isolates were serogrouped by both laboratories using the multiplex PCR assay described by Doumith et al. (2004) [4] which clusters L. monocytogenes lineages I and II into four serogroups by amplification of four specific marker genes: buy Erastin lmo0737; ORF2110; lmo1118 and ORF2819. Fluorescent AFLP FAFLP was performed by the UK-NRL using a modified version of the protocol previously described by Desai and colleagues for Campylobacter[12]. Briefly, Listeria genomic DNA (15–50 ng) was digested with 5U each of two restriction enzymes, HindIII and HhaI (New England Biolabs) in the presence of RNase A and bovine serum albumin. Digests were ligated to two sets of double-stranded adapters. These adapters served as targets for an FAM-labeled Hind-A and a non-labeled Hha-A selective primer Resveratrol (Eurogentec, Seraing) for fragment amplification by PCR. The modified protocol consisted of

a single digestion/ligation rather than 3 individual steps as previously described [12]. Fluorescent PCR products (amplified digested fragments) were separated on an ABI 3730XL 96 capillary DNA Analyzer (Applied Biosystems) alongside a GeneScan™- 600 LIZ® Size standard. Chromatographs showing FAM-fluorescing fragments were saved as fsa files, and were exported, visualized and analyzed using PEAK SCANNER™ v1.0 (Applied Biosystems). PEAK SCANNER™ also recorded the fragment data in a binary format in Excel files which were exported into BioNumerics v6.1, visualized as virtual electrophoresis gels and analyzed. The patterns determining the fAFLP types were identified using in-house BioNumerics and PEAK SCANNER™ libraries. Two profiles were considered to be different fAFLP types if they had at least one peak difference.