Abstract
Brucella, a Gram-negative bacterium with a high infective capacity and a wide spectrum of hosts in the animal world, is found in terrestrial and marine mammals, as well as amphibians. This broad spectrum of hosts is closely related to the non-classical virulence factors that allow this pathogen to establish its replicative niche, colonizing epithelial and immune system cells, evading the host’s defenses and defensive response. While motility is the primary role of the flagellum in most bacteria, in Brucella, the flagellum is involved in virulence, infectivity, cell growth, and biofilm formation, all of which are very important facts in a bacterium that to date has been described as a non-motile organism. Evidence of the expression of these flagellar proteins that are present in Brucella makes it possible to hypothesize certain evolutionary aspects as to where a free-living bacterium eventually acquired genetic material from environmental microorganisms, including flagellar genes, conferring on it the ability to reach other hosts (mammals), and, under selective pressure from the environment, can express these genes, helping it to evade the immune response. This review summarizes relevant aspects of the presence of flagellar proteins and puts into context their relevance in certain functions associated with the infective process. The study of these flagellar genes gives the genus Brucella a very high infectious versatility, placing it among the main organisms in urgent need of study, as it is linked to human health by direct contact with farm animals and by eventual transmission to the general population, where flagellar genes and proteins are of great relevance.
Highlights
Brucella abortus is a Gram-negative, non-motile, coccobacillary bacterium and a facultative intracellular pathogen, causing disease in both animals and humans [1]
Many new species of Brucella have been discovered, mainly pathogens of marine mammals and others capable of infecting terrestrial mammals, in addition to flagellated species present in amphibians [86]. This complicates the execution of control programs since the recently characterized Brucella species have high genetic flexibility and many of these isolates are motile, fast-growing, able to survive in the soil, more resistant to unfavorable conditions of environmental acidity, and more able to adapt to new nonmammalian hosts, such as amphibians, rapidly adapting to their environment to broaden their host range [87]
Brucella is characterized as being a stealthy microbe that tends to chronicity, instead of causing an acute fatal infection, standing out for being a successful microorganism by evading the immune response and keeping its hosts alive to maintain its own survival
Summary
Brucella abortus is a Gram-negative, non-motile, coccobacillary bacterium and a facultative intracellular pathogen, causing disease in both animals and humans [1]. It can infect humans, and diagnosis is difficult [2] This disease can be characterized by its ability to become a chronic infection, which in bovines can cause abortions, stillbirths, the birth of weak calves, and sterility in males [3]. A decade ago, the genus contained six “classic” Brucella species (B. melitensis, B. abortus, B. suis, B. canis, B. ovis, and B. neotomae), which are known as the “core” Brucella. Three of these species (B. melitensis, B. abortus and B. suis) are the pathogens that cause one of the most significant zoonoses worldwide [14]. An interesting finding was made regarding this bacterium, generally classified as non-motile, in terms of the expression of flagellar genes and a polar flagellum under certain conditions
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