Molecular, cellular and neurological consequences of infection by the neglected human pathogen Nocardia

Abstract

Background Nocardia is a facultative intracellular pathogen that infects the lungs and brains of immunocompromised patients with consequences that can be fatal. The incidence of such infections is rising, immunocompetent individuals are also being infected, and there is a need to learn more about this neglected bacterial pathogen and the interaction with its human host. Results We have applied dual RNA-seq to assess the global transcriptome changes that occur simultaneously in Nocardia farcinica (N. farcinica) and infected human epithelial alveolar host cells, and have tested a series of mutants in this in vitro system to identify candidate determinants of virulence. Using a mouse model, we revealed the profiles of inflammation-related factors in the lung after intranasal infection and confirmed that nbtB and nbtS are key virulence genes for Nocardia infection in vivo. Regarding the host response to infection, we found that the expression of many histones was dysregulated during the infection of lung cells, indicating that epigenetic modification might play a crucial role in the host during Nocardia infection. In our mouse model, Nocardia infection led to neurological symptoms and we found that 15 of 22 Nocardia clinical strains tested could cause obvious PD-like symptoms. Further experiments indicated that Nocardia infection could activate microglia and drive M1 microglial polarization, promote iNOS and CXCL-10 production, and cause neuroinflammation in the substantia nigra, all of which may be involved in causing PD-like symptoms. Importantly, the deletion of nbtS in N. farcinica completely attenuated the neurological symptoms. Conclusions Our data contribute to an in-depth understanding of the characteristics of both the host and Nocardia during infection and provide valuable clues for future studies of this neglected human pathogen, especially those addressing the underlying causes of infection-related neurological symptoms.

Epidemiology, Timing, and Secondary Prophylaxis of Recurrent Nocardiosis

“…Nocardia species are a group of partially acid-fast, intracellular pathogens with an incidence up to 0.87 cases per 100 000 people annually [ 1 , 2 ]. Nocardia species have multiple virulence factors that contribute to its ability to evade the host immune response [ 3 ]. In addition, adaptive lymphocyte immunity appears essential for clearance of Nocardia organisms, which is often impaired in immunocompromised populations at risk for nocardiosis [ 4–7 ].…”

Outcomes of transplant recipients with pretransplant Nocardia colonization or infection

“…10,11,[13][14][15] As an intracellular pathogen with the capability to evade host immune response that relies on cellular immunity, Nocardia recurrence has been described in approximately 5% of SOT recipients. 14,16,17 However, little data exist regarding any impact of pretransplant Nocardia infection or colonization on posttransplant outcomes.…”

“…Importantly, nocardiosis has been associated with increased mortality among transplant recipients, with several factors such as underlying comorbidities increasing this risk 10,11,13–15 . As an intracellular pathogen with the capability to evade host immune response that relies on cellular immunity, Nocardia recurrence has been described in approximately 5% of SOT recipients 14,16,17 . However, little data exist regarding any impact of pretransplant Nocardia infection or colonization on posttransplant outcomes.…”