The NOD-scid IL2rγnull Mouse Model Is Suitable for the Study of Osteoarticular Brucellosis and Vaccine Safety

Next-Generation Sequencing-Based Identification of Enterobacter hormaechei as Causative Agent of High Mortality Disease in NOD.Cg-PrkdcscidIl2rgtm1Wjl/SzJ (NSG) Mice

NOD.Cg-PrkdcscidIl2rgtm1Wjl/SzJ (NSG) mice, lacking many components of a mature immune system, are at increased risk of disease. General understanding of potential pathogens of these mice is limited. We describe a high mortality disease outbreak caused by an opportunistic bacterial infection in NSG mice. Affected animals exhibited perianal fecal staining, dehydration, and wasting. Histopathologic lesions included a primary necrotizing enterocolitis, with inflammatory and necrotizing lesions also occurring in the liver, kidneys, heart, and brain of some mice. All affected individuals tested negative for known opportunistic pathogens of immunodeficient mice. We initially identified a member of Enterobacter cloacae complex (ECC) in association with the outbreak by traditional diagnostics. ECC was cultured from extraintestinal organs, both with and without histopathologic lesions, suggesting bacteremia. Infrared spectroscopy and MALDI-TOF mass spectrometry demonstrated that isolates from the outbreak shared molecular features and likely a common origin. We subsequently hypothesized that advanced sequencing methods would identify a single species of ECC associated with clinical disease. Using a novel targeted amplicon-based next-generation sequencing assay, we identified Enterobacter hormaechei in association with this outbreak. Knowledge of this organism as a potential opportunistic pathogen in NSG mice is critical for preclinical studies to prevent loss of animals and confounding of research.

Interaction of Brucella abortus with Osteoclasts: a Step toward Understanding Osteoarticular Brucellosis and Vaccine Safety

Osteoarticular disease is a frequent complication of human brucellosis. Vaccination remains a critical component of brucellosis control, but there are currently no vaccines for use in humans, and no in vitro models for assessing the safety of candidate vaccines in reference to the development of bone lesions currently exist. While the effect of Brucella infection on osteoblasts has been extensively evaluated, little is known about the consequences of osteoclast infection. Murine bone marrow-derived macrophages were derived into mature osteoclasts and infected with B. abortus 2308, the vaccine strain S19, and attenuated mutants S19vjbR and B. abortus ΔvirB2 While B. abortus 2308 and S19 replicated inside mature osteoclasts, the attenuated mutants were progressively killed, behavior that mimics infection kinetics in macrophages. Interestingly, B. abortus 2308 impaired the growth of osteoclasts without reducing resorptive activity, while osteoclasts infected with B. abortus S19 and S19vjbR were significantly larger and exhibited enhanced resorption. None of the Brucella strains induced apoptosis or stimulated nitric oxide or lactose dehydrogenase production in mature osteoclasts. Finally, infection of macrophages or osteoclast precursors with B. abortus 2308 resulted in generation of smaller osteoclasts with decreased resorptive activity. Overall, Brucella exhibits similar growth characteristics in mature osteoclasts compared to the primary target cell, the macrophage, but is able to impair the maturation and alter the resorptive capacity of these cells. These results suggest that osteoclasts play an important role in osteoarticular brucellosis and could serve as a useful in vitro model for both analyzing host-pathogen interactions and assessing vaccine safety.

Immune Response to Mucosal Brucella Infection

Brucellosis is one of the most prevalent bacterial zoonosis of worldwide distribution. The disease is caused by Brucella spp., facultative intracellular pathogens. Brucellosis in animals results in abortion of fetuses, while in humans, it frequently manifests flu-like symptoms and a typical undulant fever, being osteoarthritis a common complication of the chronic infection. The two most common ways to acquire the infection in humans are through the ingestion of contaminated dairy products or by inhalation of contaminated aerosols. Brucella spp. enter the body mainly through the gastrointestinal and respiratory mucosa; however, most studies of immune response to Brucella spp. are performed analyzing models of systemic immunity. It is necessary to better understand the mucosal immune response induced by Brucella infection since this is the main entry site for the bacterium. In this review, some virulence factors and the mechanisms needed for pathogen invasion and persistence are discussed. Furthermore, some aspects of local immune responses induced during Brucella infection will be reviewed. With this knowledge, better vaccines can be designed focused on inducing protective mucosal immune response.