Introduction: Epidemic clones (ECs) of Listeria monocytogenes group genetically related isolates, presumably of a common ancestor that have been implicated in different unrelated outbreaks for the past 30 years (Kathariou, 2002). For ECs discrimination, six single nucleotide polymorphisms (SNPs) that were able to differentiate a specific EC from unrelated strains were defined as informative (Lomonaco et al., 2008). A novel multiplex SNP-based assay was recently developed, which interrogated these six informative SNPs (Lomonaco et al., 2011). This assay correctly and specifically identified all 4 previously identified ECs, and also identified nine strains as ECs, which had previously been misclassified. All other non-EC strains shared one or more common SNP profiles, different from those of ECs (Lomonaco et al., 2011). Purpose: Since then, another EC (ECV) has been identified (Knabel et al., 2012). In silico determination of the ECV SNP-profile using available whole-genome sequences (Gilmour et al. 2010) showed that the above six selected SNPs would also provide a specific profile for ECV. The objective of this study was to test the novel multiplex SNP-typing assay for identification of ECV. Methods: SNP-typing was conducted on 49 ECV isolates that had been previously tested with ECV-specific PCR and multi-virulence-locus sequence typing - MVLST (Knabel et al., 2012). One isolate previously found positive by PCR but not confirmed by MVLST was also included (Knabel et al., 2012). Results: The SNP-based screening revealed a ECV-specific profile for all 50 isolates, including the false-positive ECV sample, thus showing 100% sensibility and 98% specificity. Significance: Further tests on a wider selection of L. monocytogenes isolates from different sources will be needed to confirm these preliminary findings. Notwithstanding, this novel multiplex SNP-typing can be a valuable tool to rapidly screen for all five currently known ECs of L. monocytogenes. Detection and differentiation of strains of L. monocytogenes, in particular detection of ECs, will be critical for the implementation of more efficient strategies to reduce contamination and thus improving the safety of food products. Funds kindly provided by Prof.ssa Grassi (grant "Quality Milk", Regione Piemonte, POR-FESR Asse I, Innovazione e transizione produttiva 2010-2013).
Novel multiplex SNP-based method allows identification of the newly characterized epidemic clone V of Listeria monocytogenes
LOMONACO, Sara;
2012-01-01
Abstract
Introduction: Epidemic clones (ECs) of Listeria monocytogenes group genetically related isolates, presumably of a common ancestor that have been implicated in different unrelated outbreaks for the past 30 years (Kathariou, 2002). For ECs discrimination, six single nucleotide polymorphisms (SNPs) that were able to differentiate a specific EC from unrelated strains were defined as informative (Lomonaco et al., 2008). A novel multiplex SNP-based assay was recently developed, which interrogated these six informative SNPs (Lomonaco et al., 2011). This assay correctly and specifically identified all 4 previously identified ECs, and also identified nine strains as ECs, which had previously been misclassified. All other non-EC strains shared one or more common SNP profiles, different from those of ECs (Lomonaco et al., 2011). Purpose: Since then, another EC (ECV) has been identified (Knabel et al., 2012). In silico determination of the ECV SNP-profile using available whole-genome sequences (Gilmour et al. 2010) showed that the above six selected SNPs would also provide a specific profile for ECV. The objective of this study was to test the novel multiplex SNP-typing assay for identification of ECV. Methods: SNP-typing was conducted on 49 ECV isolates that had been previously tested with ECV-specific PCR and multi-virulence-locus sequence typing - MVLST (Knabel et al., 2012). One isolate previously found positive by PCR but not confirmed by MVLST was also included (Knabel et al., 2012). Results: The SNP-based screening revealed a ECV-specific profile for all 50 isolates, including the false-positive ECV sample, thus showing 100% sensibility and 98% specificity. Significance: Further tests on a wider selection of L. monocytogenes isolates from different sources will be needed to confirm these preliminary findings. Notwithstanding, this novel multiplex SNP-typing can be a valuable tool to rapidly screen for all five currently known ECs of L. monocytogenes. Detection and differentiation of strains of L. monocytogenes, in particular detection of ECs, will be critical for the implementation of more efficient strategies to reduce contamination and thus improving the safety of food products. Funds kindly provided by Prof.ssa Grassi (grant "Quality Milk", Regione Piemonte, POR-FESR Asse I, Innovazione e transizione produttiva 2010-2013).
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