title: Increased spread and replication efficiency of Listeria monocytogenes in organotypic brain-slices is related to multilocus variable number of tandem repeat analysis (MLVA) complex.
abstract: BACKGROUND
  Listeria (L.) monocytogenes causes fatal infections in many species including ruminants and humans. In ruminants, rhombencephalitis is the most prevalent form of listeriosis. Using multilocus variable number tandem repeat analysis (MLVA) we recently showed that L. monocytogenes isolates from ruminant rhombencephalitis cases are distributed over three genetic complexes (designated A, B and C). However, the majority of rhombencephalitis strains and virtually all those isolated from cattle cluster in MLVA complex A, indicating that strains of this complex may have increased neurotropism and neurovirulence. The aim of this study was to investigate whether ruminant rhombencephalitis strains have an increased ability to propagate in the bovine hippocampal brain-slice model and can be discriminated from strains of other sources. For this study, forty-seven strains were selected and assayed on brain-slice cultures, a bovine macrophage cell line (BoMac) and a human colorectal adenocarcinoma cell line (Caco-2). They were isolated from ruminant rhombencephalitis cases (n = 21) and other sources including the environment, food, human neurolisteriosis cases and ruminant/human non-encephalitic infection cases (n = 26).
  
  
  RESULTS
  All but one L. monocytogenes strain replicated in brain slices, irrespectively of the source of the isolate or MLVA complex. The replication of strains from MLVA complex A was increased in hippocampal brain-slice cultures compared to complex C. Immunofluorescence revealed that microglia are the main target cells for L. monocytogenes and that strains from MLVA complex A caused larger infection foci than strains from MLVA complex C. Additionally, they caused larger plaques in BoMac cells, but not CaCo-2 cells.
  
  
  CONCLUSIONS
  Our brain slice model data shows that all L. monocytogenes strains should be considered potentially neurovirulent. Secondly, encephalitis strains cannot be conclusively discriminated from non-encephalitis strains with the bovine organotypic brain slice model. The data indicates that MLVA complex A strains are particularly adept at establishing encephalitis possibly by virtue of their higher resistance to antibacterial defense mechanisms in microglia cells, the main target of L. monocytogenes.
authors.affiliation: Division of Neurological Sciences, Neurocenter, Department of Clinical Research and Veterinary Public Health, Vetsuisse Faculty, University of Bern, Bern, Switzerland. cg445@cornell.edu.|Graduate school for Cellular and Biomedical Sciences, University of Bern, Bern, Switzerland. cg445@cornell.edu.
authors.forename: Claudia
authors.initials: C
authors.lastname: Guldimann
authors.affiliation: Division of Neurological Sciences, Neurocenter, Department of Clinical Research and Veterinary Public Health, Vetsuisse Faculty, University of Bern, Bern, Switzerland. michelle.baertschi@vetsuisse.unibe.ch.
authors.forename: Michelle
authors.initials: M
authors.lastname: Bärtschi
authors.affiliation: Institute of Veterinary Bacteriology, Vetsuisse Faculty, University of Bern, Bern, Switzerland. joachim.frey@vetsuisse.unibe.ch.
authors.forename: Joachim
authors.initials: J
authors.lastname: Frey
authors.affiliation: Division of Neurological Sciences, Neurocenter, Department of Clinical Research and Veterinary Public Health, Vetsuisse Faculty, University of Bern, Bern, Switzerland. andreas.zurbriggen@vetsuisse.unibe.ch.
authors.forename: Andreas
authors.initials: A
authors.lastname: Zurbriggen
authors.affiliation: Division of Neurological Sciences, Neurocenter, Department of Clinical Research and Veterinary Public Health, Vetsuisse Faculty, University of Bern, Bern, Switzerland. torsten.seuberlich@vetsuisse.unibe.ch.
authors.forename: Torsten
authors.initials: T
authors.lastname: Seuberlich
authors.affiliation: Division of Neurological Sciences, Neurocenter, Department of Clinical Research and Veterinary Public Health, Vetsuisse Faculty, University of Bern, Bern, Switzerland. anna.oevermann@vetsuisse.unibe.ch.
authors.forename: Anna
authors.initials: A
authors.lastname: Oevermann
mesh_terms: D000818:Animals; D001921:Brain / Q000382:microbiology*; D002417:Cattle; D002418:Cattle Diseases / Q000382:microbiology*; D002478:Cells, Cultured; D004660:Encephalitis / Q000382:microbiology / Q000662:veterinary*; D004847:Epithelial Cells / Q000382:microbiology; D005838:Genotype; D006801:Humans; D008089:Listeria monocytogenes / Q000145:classification* / Q000235:genetics / Q000472:pathogenicity*; D008088:Listeriosis / Q000382:microbiology / Q000662:veterinary*; D008264:Macrophages / Q000382:microbiology; D018598:Minisatellite Repeats; D014774:Virulence