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Abstract
BackgroundListeria (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).ResultsAll 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.ConclusionsOur 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-015-0454-0) contains supplementary material, which is available to authorized users.
Highlights
Listeria (L.) monocytogenes causes fatal infections in many species including ruminants and humans
L. monocytogenes is commonly isolated in the context of meningitis [6], and neurolisteriosis is responsible for high fatality rates and chronic sequelae [7,8,9,10]
Infection of organotypic brain-slice cultures with L. monocytogenes strains We analyzed replication and capacity to spread in organotypic hippocampal brain-slice cultures of 21 L. monocytogenes strains isolated from ruminant rhombencephalitis cases and 26 strains of ruminant non-encephalitic cases, human clinical infections or food/environment (Additional file 1)
Summary
Listeria (L.) monocytogenes causes fatal infections in many species including ruminants and humans. 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). The Gram + bacterium Listeria (L.) monocytogenes is an opportunistic food-borne pathogen with considerable impact on human and livestock health and food safety It causes listeriosis [1,2], which may manifest in distinct clinical forms including febrile gastroenteritis, abortions, septicemia, and neurolisteriosis [2,3] and is associated with high mortality [4,5]. Rhombencephalitis generally occurs without involvement of other organs and without inducing abortion in pregnant ruminants [17,18,19]
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