Date Published: April 3, 2019
Publisher: Public Library of Science
Author(s): Steven Grant Waldrop, Nammalwar Sriranganathan, Abdallah M. Samy.
In 1967, Brucella neotomae was first isolated from Neotoma lepida, the dessert wood rat, in Utah. With little infection data since its discovery, the zoonotic potential of this Brucella species is largely unknown. Recent reports of isolation from human cerebrospinal fluid, along with current literature suggest that B. neotomae has the ability to infect various hosts and cell types. In this report we extend the knowledge of B. neotomae ATCC 23459’s intracellular invasion and survival abilities to a variety of cell lines through gentamicin protection assays. Some of the phagocytic and epithelial cell lines from various mammalian species represent characteristics of some cell types that could be encountered by Brucella in potential hosts. It was found that B. neotomae ATCC 23459 exhibits generally lower intracellular bacterial CFUs compared to the mouse-passaged strain of B. neotomae ATCC 23459, B. suis 1330, and B. abortus 2308. Ultimately, these observations provide a small piece of the puzzle in the investigation of the breadth of B. neotomae’s pathogenic potential.
The genus Brucella is composed of Gram-negative, non-sporulating, non-motile cocco-bacilli that lack a capsule from the alpha-proteobacteria group. This group is composed of a variety of bacterial species that are generally associated, but not obligated to specific hosts. The hosts of Brucella spp. range widely and include rodents, ungulates, marine mammals, and humans. There are currently 11 accepted species of Brucella: B. melitensis, B. abortus, B. suis, B. canis, B. inopinata, B. ovis, B. neotomae, B. pinnipedialis, B. ceti, and B. microti. Many are considered zoonotic with around 500,000 cases of human brucellosis reported worldwide each year .
Cell culture is widely used as a representative model for microorganism’s infectivity and is especially important in helping predict the range of pathogenicity of atypical Brucella species [16, 35–37]. Invasion and replication in epithelial cells and macrophages are vital in Brucella infections, although they are just one aspect to virulence [16, 37]. Other aspects important to virulence are the type IV secretion system and the LPS O-side chain [11, 13, 23, 35, 36]. Current literature supports that B. neotomae possesses these virulence factors [4, 16, 35]. B. neotomae has also been shown to have type IV dependent intracellular survival and a similar late endoplasmic reticulum associated phagosome stage to that of other virulent Brucella spp. . Ultimately, it was expected to see B. neotomae strains have the ability to survive within phagocytic and epithelial cell lines in a similar manor to other virulent species, especially with current literature showing that it can infect humans, swine, rodents, and bison [11, 12, 14, 20, 24, 37]. Our intracellular invasion and survival profiles of B. neotomae add to the evidence in current literature warranting further characterization of its pathogenic ability. Our data aligns with current literature and extends the known intracellular uptake and survival profiles of the Brucella species to include a breadth of cell lines [38–46].