title: Genome sequencing identifies two nearly unchanged strains of persistent Listeria monocytogenes isolated at two different fish processing plants sampled 6 years apart.
abstract: Listeria monocytogenes is a food-borne human-pathogenic bacterium that can cause infections with a high mortality rate. It has a remarkable ability to persist in food processing facilities. Here we report the genome sequences for two L. monocytogenes strains (N53-1 and La111) that were isolated 6 years apart from two different Danish fish processers. Both strains are of serotype 1/2a and belong to a highly persistent DNA subtype (random amplified polymorphic DNA [RAPD] type 9). We demonstrate using in silico analyses that both strains belong to the multilocus sequence typing (MLST) type ST121 that has been isolated as a persistent subtype in several European countries. The purpose of this study was to use genome analyses to identify genes or proteins that could contribute to persistence. In a genome comparison, the two persistent strains were extremely similar and collectively differed from the reference lineage II strain, EGD-e. Also, they differed markedly from a lineage I strain (F2365). On the proteome level, the two strains were almost identical, with a predicted protein homology of 99.94%, differing at only 2 proteins. No single-nucleotide polymorphism (SNP) differences were seen between the two strains; in contrast, N53-1 and La111 differed from the EGD-e reference strain by 3,942 and 3,471 SNPs, respectively. We included a persistent L. monocytogenes strain from the United States (F6854) in our comparisons. Compared to nonpersistent strains, all three persistent strains were distinguished by two genome deletions: one, of 2,472 bp, typically contains the gene for inlF, and the other, of 3,017 bp, includes three genes potentially related to bacteriocin production and transport (lmo2774, lmo2775, and the 3'-terminal part of lmo2776). Further studies of highly persistent strains are required to determine if the absence of these genes promotes persistence. While the genome comparison did not point to a clear physiological explanation of the persistent phenotype, the remarkable similarity between the two strains indicates that subtypes with specific traits are selected for in the food processing environment and that particular genetic and physiological factors are responsible for the persistent phenotype.
authors: National Food Institute, Technical University of Denmark, Kgs. Lyngby, Denmark.
authors: Anne
authors: A
authors: Holch
authors: Kristen
authors: K
authors: Webb
authors: Oksana
authors: O
authors: Lukjancenko
authors: David
authors: D
authors: Ussery
authors: Benjamin M
authors: BM
authors: Rosenthal
authors: Lone
authors: L
authors: Gram
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics; D015373:Bacterial Typing Techniques; D001483:Base Sequence; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification; D003718:Denmark; D005516:Food Microbiology; D005519:Food Preservation; D005525:Food-Processing Industry; D016680:Genome, Bacterial / Q000235:genetics*; D059014:High-Throughput Nucleotide Sequencing; D006801:Humans; D008089:Listeria monocytogenes / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification; D008088:Listeriosis / Q000382:microbiology*; D008969:Molecular Sequence Data; D058885:Multilocus Sequence Typing; D020641:Polymorphism, Single Nucleotide; D019105:Random Amplified Polymorphic DNA Technique; D012474:Salmon / Q000382:microbiology*; D017747:Seafood / Q000382:microbiology*; D017422:Sequence Analysis, DNA; D013997:Time Factors
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial