Ruminant organotypic brain‐slice cultures as a model for the investigation of CNS listeriosis

Abstract

Summary Central nervous system (CNS) infections in ruminant livestock, such as listeriosis, are of major concern for veterinary and public health. To date, no host‐specific in vitro models for ruminant CNS infections are available. Here, we established and evaluated the suitability of organotypic brain‐slices of ruminant origin as in vitro model to study mechanisms of Listeria monocytogenes CNS infection. Ruminants are frequently affected by fatal listeric rhombencephalitis that closely resembles the same condition occurring in humans. Better insight into host–pathogen interactions in ruminants is therefore of interest, not only from a veterinary but also from a public health perspective. Brains were obtained at the slaughterhouse, and hippocampal and cerebellar brain‐slices were cultured up to 49 days. Viability as well as the composition of cell populations was assessed weekly. Viable neurons, astrocytes, microglia and oligodendrocytes were observed up to 49 days in vitro. Slice cultures were infected with L. monocytogenes, and infection kinetics were monitored. Infected brain cells were identified by double immunofluorescence, and results were compared to natural cases of listeric rhombencephalitis. Similar to the natural infection, infected brain‐slices showed focal replication of L. monocytogenes and bacteria were predominantly observed in microglia, but also in astrocytes, and associated with axons. These results demonstrate that organotypic brain‐slice cultures of bovine origin survive for extended periods and can be infected easily with L. monocytogenes. Therefore, they are a suitable model to study aspects of host–pathogen interaction in listeric encephalitis and potentially in other neuroinfectious diseases.

Listeria monocytogenes Spreads within the Brain by Actin-Based Intra-Axonal Migration

“…We hypothesized that this may in part be related to the ability of the agent to spread intracere- brally inside axons, allowing the agent to escape the immune response at least temporarily. As our previously reported neuropathological observations and infection assays of hippocampal brain slices suggested that intra-axonal spread of L. monocytogenes may also occur in the CNS (17,30), the present study was designed to explore this hypothesis by neuroanatomical mapping of the lesions, precise localization of L. monocytogenes bacteria, and in vitro infections of brain cells.…”

“…The efficient spread of L. monocytogenes could be explained by its ability to move from cell to cell, which permits the agent to multiply and diffuse within tissues protected from the host defenses by avoiding contact with the extracellular compartment (19). In view of the observed ability of L. monocytogenes to spread within cranial nerves (25,26), our previous studies showing progression of the lesions within the brain (17) and the sporadic association of L. monocytogenes with axons in the hippocampal slice model (30), we hypothesized that intercellular spread of the agent in the CNS could also be intra-axonal. Moving within axons, a highly interconnected network with little or no major histocompatibility complex (MHC) expression (29,31), would, at least temporarily, allow L. monocytogenes to escape immune detection while efficiently spreading to distant CNS regions.…”

Spreading of multiple Listeria monocytogenes abscesses via central nervous system fiber tracts: case report

“…In fact, in one study, peripheral neurons were able to be effectively infected, contrary to hippocampal neurons, which were resistant, suggesting that different types of neurons might have different susceptibilities to bacterial tropism. 13,17 A recent animal study, however, suggests that once the bacteria have gained access to the CNS via the peripheral nervous system, the infection can spread along the axons, producing additional lesions. 17,32 This hypothesis has not previously been evaluated in humans.…”

“…13,17 A recent animal study, however, suggests that once the bacteria have gained access to the CNS via the peripheral nervous system, the infection can spread along the axons, producing additional lesions. 17,32 This hypothesis has not previously been evaluated in humans. Our results based on MRI in cases of multiple brain abscesses strongly suggest that this intraneural mechanism of spreading in the CNS also applies to humans.…”

“…12 L. monocytogenes is able to survive and multiply in a wide variety of cell types, including macrophages and neurons. 13,17,32 Even though studies have suggested that L. monocytogenes can use a peripheral intraneural route to invade the CNS, it has not yet been established how it then spreads throughout the brain. In fact, in one study, peripheral neurons were able to be effectively infected, contrary to hippocampal neurons, which were resistant, suggesting that different types of neurons might have different susceptibilities to bacterial tropism.…”