Persistence of Brucella abortus in the Bone Marrow of Infected Mice

Area of Science:

• Microbiology
• Immunology
• Infectious Diseases

Background:

• Brucellosis is a zoonotic bacterial infection known for persistent infections and relapses, even after antibiotic treatment.
• The ability of Brucella to establish chronic infections is linked to its capacity to invade and replicate within the mononuclear phagocyte system, including bone marrow (BM).
• Brucella persistence in the BM is associated with hematological complications like neutropenia, thrombocytopenia, anemia, and pancytopenia in human patients.

Purpose of the Study:

• To investigate the role of the bone marrow (BM) as a niche for Brucella persistence.
• To identify the specific cell types within the BM that harbor Brucella during chronic infection.
• To explore the mechanisms by which Brucella establishes long-lasting infections in the BM.

Main Methods:

• Utilized a mouse model to study Brucella abortus infection.
• Monitored Brucella numbers in the BM up to 168 days postinfection.
• Performed histopathological analysis of the BM.
• Quantified specific cell populations including myeloid GMP progenitors, PMNs, and CD4+ lymphocytes.
• Identified Brucella-harboring cells within the BM.

Main Results:

• Brucella abortus numbers remained constant in the BM for up to 168 days postinfection.
• Persistence was associated with histopathological changes in the BM.
• An increased number of BM myeloid GMP progenitors, PMNs, and CD4+ lymphocytes were observed during the acute phase of infection.
• Monocytes, PMNs, and GMP cells were identified as the primary cells harboring Brucella in the BM.

Conclusions:

• The bone marrow (BM) serves as an essential niche for Brucella to establish long-lasting infections.
• Infected PMNs (polymorphonuclear neutrophils) may act as 'Trojan horses' for Brucella dispersion.
• Monocytes are identified as strong candidates for Brucella reservoirs within the BM, contributing to chronic infection persistence.