title: Listeria monocytogenes associated with New Zealand seafood production and clinical cases: unique sequence types, truncated InlA, and attenuated invasiveness.
abstract: Listeriosis is caused by the food-borne pathogen Listeria monocytogenes, which can be found in seafood and processing plants. To evaluate the risk to human health associated with seafood production in New Zealand, multi-virulence-locus sequence typing (MVLST) was used to define the sequence types (STs) of 31 L. monocytogenes isolates collected from seafood-processing plants, 15 from processed foods, and 6 from human listeriosis cases. The STs of these isolates were then compared with those from a collection of seafood isolates and epidemic strains from overseas. A total of 17 STs from New Zealand clustered into two lineages: seafood-related isolates in lineages I and II and all human isolates in lineage II. None of the New Zealand STs matched previously described STs from other countries. Isolates (belonging to ST01-N and ST03-N) from mussels and their processing environments, however, were identical to those of sporadic listeriosis cases in New Zealand. ST03-N isolates (16 from mussel-processing environments, 2 from humans, and 1 from a mussel) contained an inlA premature stop codon (PMSC) mutation. Therefore, the levels of invasiveness of 22 isolates from ST03-N and the three other common STs were compared using human intestinal epithelial Caco-2 cell lines. STs carrying inlA PMSCs, including ST03-N isolates associated with clinical cases, had a low invasion phenotype. The close relatedness of some clinical and environmental strains, as revealed by identical MVLST profiles, suggests that local and persistent environmental strains in seafood-processing environments pose a potential health risk. Furthermore, a PMSC in inlA does not appear to give L. monocytogenes a noninvasive profile.
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited, Auckland, New Zealand.
authors.forename: Cristina D
authors.initials: CD
authors.lastname: Cruz
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Pitman
authors.forename: Sally A
authors.initials: SA
authors.lastname: Harrow
authors.forename: Graham C
authors.initials: GC
authors.lastname: Fletcher
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics*; D018938:Caco-2 Cells; D016000:Cluster Analysis; D018389:Codon, Nonsense; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004847:Epithelial Cells / Q000382:microbiology; D005838:Genotype; D006801:Humans; D008089:Listeria monocytogenes / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification* / Q000472:pathogenicity; D008088:Listeriosis / Q000382:microbiology*; D008969:Molecular Sequence Data; D058885:Multilocus Sequence Typing; D009520:New Zealand; D017747:Seafood / Q000382:microbiology*; D017422:Sequence Analysis, DNA; D014774:Virulence; D037521:Virulence Factors / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins; D018389:Codon, Nonsense; D004269:DNA, Bacterial; D037521:Virulence Factors; C069761:internalin protein, Bacteria