Burkholderia pseudomallei invades the olfactory nerve and bulb after epithelial injury in mice and causes the formation of multinucleated giant glial cells in vitro

Abstract

The infectious disease melioidosis is caused by the bacterium Burkholderia pseudomallei. Melioidosis is characterised by high mortality and morbidity and can involve the central nervous system (CNS). We have previously discovered that B. pseudomallei can infect the CNS via the olfactory and trigeminal nerves in mice. We have shown that the nerve path is dependent on mouse strain, with outbred mice showing resistance to olfactory nerve infection. Damage to the nasal epithelium by environmental factors is common, and we hypothesised that injury to the olfactory epithelium may increase the vulnerability of the olfactory nerve to microbial insult. We therefore investigated this, using outbred mice that were intranasally inoculated with B. pseudomallei, with or without methimazole-induced injury to the olfactory neuroepithelium. Methimazole-mediated injury resulted in increased B. pseudomallei invasion of the olfactory epithelium, and only in pre-injured animals were bacteria found in the olfactory nerve and bulb. In vitro assays demonstrated that B. pseudomallei readily infected glial cells isolated from the olfactory and trigeminal nerves (olfactory ensheathing cells and trigeminal Schwann cells, respectively). Bacteria were degraded by some cells but persisted in other cells, which led to the formation of multinucleated giant cells (MNGCs), with olfactory ensheathing cells less likely to form MNGCs than Schwann cells. Double Cap mutant bacteria, lacking the protein BimA, did not form MNGCs. These data suggest that injuries to the olfactory epithelium expose the primary olfactory nervous system to bacterial invasion, which can then result in CNS infection with potential pathogenic consequences for the glial cells.PLOS Neglected Tropical Diseases | https://doi.Infections of the central nervous system (CNS), though uncommon, are associated with severe morbidity and mortality. Burkholderia pseudomallei, the causative agent of melioidosis, can infect the CNS. We have shown that B. pseudomallei can enter the CNS via peripheral nerves extending between the nasal cavity and the brain (bypassing the bloodbrain/blood-cerebrospinal fluid barriers). In the current study, we show that prior injury to the olfactory epithelium can increase B. pseudomallei invasion of the olfactory nerve and bulb, highlighting a novel risk factor for CNS infections. We also demonstrate the ability of peripheral nerve glia to internalise B. pseudomallei, resulting in the formation of multinucleated giant cells (MNGCs), dependent on the bacterial protein BimA. These findings provide important new insights into the pathogenesis of B. pseudomallei.B. pseudomallei infects olfactory bulb after injury PLOS Neglected Tropical Diseases | https://doi.

Multinucleated Giant Cell Formation as a Portal to Chronic Bacterial Infections

“…Within a mammalian host, Bpm is a facultative intracellular pathogen that can invade and survive within nearly all cell types, phagocytic and nonphagocytic alike [ 9 , 10 ]. Whitely et al demonstrated the ability of Bpm and the closely related BSL2 pathogen Burkholderia thailandensis to establish an infection in a variety of primary cell lines and noted that the bacteria thrived in bronchial epithelial and vein endothelial cells, suggesting these locations as possible in vivo colonization sites [ 9 ].…”

“…Central nervous system (CNS) involvement is relatively rare in human melioidosis but more common in chronic murine models. It has been demonstrated that Bpm invades the olfactory bulb and can fuse glial cells [ 10 ]. Micro-abscesses in the white matter and thickening of the trigeminal nerve has been observed in human patients with CNS melioidosis, suggesting that Bpm invades the CNS through axon transport and bypassing the blood–brain barrier [ 53 ].…”

Chlamydia muridarum Can Invade the Central Nervous System via the Olfactory and Trigeminal Nerves and Infect Peripheral Nerve Glial Cells

“…The glial cells of the olfactory nerve (OECs) are hypothesized to be the key phagocytes in this nerve, and to play key roles in the protection against microorganisms ( Harris et al., 2009 ; Panni et al., 2013 ; Nazareth et al., 2015 ). The ability to infect and survive inside OECs, rather than being phagocytosed and degraded by the cells, is thought to be a feature of microorganisms that can invade the primary olfactory nervous system ( Macedo-Ramos et al., 2016 ; Walkden et al., 2020 ). Trigeminal nerve Schwann cells (TgSCs) can also phagocytose microorganisms ( Panni et al., 2013 ), however, Schwann cells have also been shown to express lower levels of mRNA for innate immune factors ( Vincent et al., 2005 ) and to mount a far weaker immune response to bacteria ( Vincent et al., 2007 ) than OECs.…”

“…Schwann cells, however, have been shown to exhibit a significantly lower immune response to pathogens than OECs ( Vincent et al., 2007 ). Some of the bacteria that can invade the olfactory/trigeminal nerves have been shown to infect rather than be cleared by OECs/TgSCs, including S. pneumoniae ( Macedo-Ramos et al., 2016 ), B. pseudomallei ( Walkden et al., 2020 ), and N. meningitidis ( Delbaz et al., 2020 ). Thus, one possibility by which Chlamydia spp.…”

Multinucleated Giant Cell Formation as a Portal to Chronic Bacterial Infections

“…Within a mammalian host, Bpm acts as an intracellular pathogen that has been shown to invade and survive within nearly all cell types and tissues; phagocytic and nonphagocytic alike [9,10,32]. Whitely et al, demonstrated the ability of Bpm and the closely related BSL2 pathogen B. thailandensis to establish an infection in a variety of primary cell lines and noted that the bacteria thrived particularly in bronchial epithelial and vein endothelial cells; suggesting those locations as possible unidentified in vivo colonization sites [9].…”