Papel do sistema de secreção tipo IV (SST4) na internalização e sobrevivência de Brucella, lisa e rugosa: infecção in vitro e in vivo

Abstract

The genus Brucella comprises intracellular bacterial pathogens that cause chronic infections. A key virulence factor required for infection establishment is the type IV secretion system (T4SS), encoded by the virB operon. Another virulence-associated factor is the lipopolysaccharide (LPS) of the outer membrane, which occurs as smooth or rough LPS. Due to the limited information available on the pathogenesis of the rough strain Brucella ovis, this study evaluated the role of T4SS in the internalization and intracellular survival of smooth and rough Brucella strains. Infections were performed in vitro (Raw 264.7 murine macrophages; 5×10⁷ CFU/ml) and in vivo (BALB/c mice infected intraperitoneally with 1×10⁶ CFU/ml) using B. ovis, ΔvirB B. ovis, RB51, ΔvirB RB51 (rough LPS), Brucella abortus, and ΔvirB B. abortus (smooth LPS). Bacteriological, histological, immunohistochemical, and qRT-PCR analyses of cytokines/chemokines (MIP-2, MIP-1α, KC, IL-6, and IL-10) were also performed. T4SS was essential for intracellular replication of rough Brucella strains, showing a role similar to that observed in smooth LPS strains such as B. abortus. Internalization was not affected by the virB operon in either smooth or rough strains. ΔvirB B. ovis mutants failed to survive and replicate in macrophages, exhibited reduced splenic colonization and pathogenicity, and were attenuated as early as 1 day post-infection in BALB/c mice. In contrast, B. abortus and ΔvirB B. abortus displayed similar in vivo infection kinetics. B. ovis did not induce early splenic or hepatic inflammation within 24 h post-infection and elicited low expression of MIP-2, MIP-1α, KC, IL-6, and IL-10. These findings demonstrate that T4SS is essential for the intracellular survival and replication of both smooth and rough Brucella strains.