Publication Database

A neonatal CNS infection model following nasal challenge with Listeria monocytogenes (2017)

Art

Hochschulschrift

Autor

Pägelow, Dennis (WE 7)

Quelle

Hannover: Bibliothek der Tierärztlichen Hochschule Hannover, 2017

Sprache

Englisch

Verweise

URL (Volltext): http://elib.tiho-hannover.de/dissertations/paegelowd_ss17.pdf

Kontakt

Institut für Mikrobiologie und Tierseuchen

Robert-von-Ostertag-Str. 7-13
14163 Berlin
+49 30 838 51843 / 66949
mikrobiologie@vetmed.fu-berlin.de

Abstract / Zusammenfassung

Listeria monocytogenes (Lm), a Gram-positive, facultative intracellular bacterium is considered to be one of the major neuroinvasive pathogens with case fatality rates up to 30% in the neonatal population. However, the routes of infection and innate immune responses in the newborn remain poorly understood.

This study was designed to establish a murine in vivo model of neonatal central nervous system (CNS) infection following mucosal challenge with Lm. Intragastric (i.g.) infection of one-day-old C57BL/6 mice with Lm induced fatal disease in a time- and dose-dependent manner, but revealed only inconsistent CNS invasion rates. In contrast, intranasal (i.n.) application resulted in frequent CNS infection and higher bacterial burden in brain tissue over time. The onset and progress of disease symptoms was also found to be less rapid. Bacterial culture revealed that Lm was able to colonize the nasal cavity and spread to liver and spleen tissue, where bacterial counts increased significantly throughout the investigated period. In contrast, Lm was infrequently detected in the blood samples, especially at early time points, where bacteria were already found in the CNS. The results of this work, together with clinical data from previous studies, suggest a novel non-hematogenous route infection of Lm into the CNS. Dissection of perfused brain tissue revealed the highest bacterial accumulation in the olfactory bulb. The bacterial counts of Lm decreased significantly along the rostro-caudal axis, with the lowest numbers found in the cerebellum. Immunohistochemistry and transmission electron microscopy revealed that the olfactory epithelium and both sustentacular cells and olfactory sensory neurons were main targets for invasion of Lm. Infected mice displayed focal spots of necrosis within the olfactory mucosa as well as purulent rhinitis and inflammation of adjacent tissues. Bacteria were found intralesionally and associated with axon bundles in the lamina propria and the cribriform plate, supporting the idea that Lm is able to migrate along olfactory nerves into the CNS of murine neonates. Lm deficient for the essential virulence factors ActA or LLO were both able to colonize the nasal cavity, but failed to invade the CNS.

Lm induced purulent-necrotizing meningoencephalitis and accumulation of CD45+CD11b+ cells, particularly in the olfactory bulb. Characterization of the molecular immune response showed a significant increase in the mRNA expression of the proinflammatory cytokines Tnfα and Cxcl2 as well as the monocyte-attracting chemokines Ccl2 and Ccl7 in brain tissues of infected mice. Further, neurolisteriosis resulted in the recruitment of Ly6C+ monocytes/macrophages to the brain.

In conclusion, we have established the first neonatal model for listerial meningoencephalitis, and identified a novel infection route of Lm to reach the CNS tissue in the murine host. Using this model, we have investigated the role of known bacterial virulence factors and characterized innate immune responses within the cerebral tissue of neonate mice with neurolisteriosis.