Figure 5.

(A) In terms of its evolutionary origin, it is postulated that Brucella may have been a free-living bacterium. (B) Over time, and according to its evolution, it remained in contact with other microorganisms, such as soil bacteria and fungi, managing to acquire certain genes that, therefore, improved its metabolic resources. (C) Environmental changes helped give it the ability to adapt to new hosts, such as eukaryotic cells. In Brucella, certain virulence factors that are different from other bacteria, like its LPS, its type-four secretion system (T4SS) and the BvrR/BvrS system, enable Brucella to interact with the host cell surface and form an early Brucella-containing vacuole (BCV) for its subsequent interaction with the endoplasmic reticulum (ER), where bacteria multiply and reach their replicative niche. Likewise, the presence of flagellar genes and the active participation of flagellum proteins in different functions, such as the translocation of proteins to the outside and the formation of adhered biofilm-associated biomass gave Brucella the ability to be a successful organism in achieving its infectious chronicity and evading the immune response of the host organism.