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P2-156 A Comprehensive Evaluation of the Genetic Relatedness of Listeria monocytogenes Serotype 4b Variant Strains

Tuesday, July 11, 2017
Exhibit Hall (Tampa Convention Center)
Laurel Burall , U.S. Food and Drug Administration - CFSAN , Laurel , MD
Christopher Grim , U.S. Food and Drug Administration, CFSAN , Laurel , MD
Mark Mammel , U.S. Food and Drug Administration , Laurel , MD
Atin Datta , U.S. Food and Drug Administration - CFSAN , Laurel , MD
Introduction: Recently, we identified a link between four listeriosis incidents and a variant of Listeria monocytogenes serotype 4b, 4bV. These 4bV strains have a 4b genomic backbone with a 6.3kb DNA segment from lineage II. Isolates from these incidents were highly related and three of these incidents involved produce. The increased association of 4bV isolates raised the concern that 4bV were more prevalent in food and clinical samples than previously thought.

Purpose: We evaluated a more comprehensive strain collection to better establish the genomic diversity of 4bV and identify trends that could be related to food contamination and human listeriosis.

Methods: 4bV isolates were identified from the NCBI Nucleotide collection (nr/nt) and SRA databases using BLASTn. Relatedness was evaluated using the CFSAN SNP Pipeline and six gene multi virulence locus sequence typing (MVLST). Phylogenetic results were compared with available metadata.

Results: A total of 367 L. monocytogenes 4bV strains were identified from either clinical isolates or BLAST interrogation of 6830 NCBI sequences. Over half of the isolates originated from clinical sources, many from apparent sporadic cases. Strains originated from the USA, Australia, and Chile. The 4bV strains diverged from traditional 4b strains and formed seven clusters when analyzed with the CFSAN SNP Pipeline. When MVLST was used to examine phylogeny, 87% belonged to a single cluster, comprised of strains from the two largest SNP-based 4bV clades. These clades represented geographically distinct regions, atypical foods, and contained historical isolates from the early 2000s.

Significance: The differing phylogenetic results suggest that 4bV strains undergo varied selection processes, restricting diversity across the six virulence loci compared to core genomic variability. These data show that 4bV includes multiple genomic groups and may have adaptations leading to improved survival in foods and/or processing environments. Such knowledge may provide guidance to better control Listeria contamination.

Back to: Poster Session 2 – Food Chemical Hazards and Food Allergens, Food Toxicology, Meat, Poultry and Eggs, Epidemiology, Retail and Food Service Safety, Communication Outreach and Education, Molecular Analytics, Genomics and Microbiome, Laboratory and Detection Methods, and Dairy
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