A Microbial Biorealm page on the genus Brucella abortus
Higher order taxa
Bacteria; Proteobacteria; Alphaproteobacteria; Rhizobiales; Brucellaceae [Others may be used. Use NCBI link to find]
Description and significance
Brucella abortus is a gram-negative bacterium that is found in cattle populations (1). This blood borne pathogen causes premature abortion of a cattle fetus. What makes this bacterium so dangerous is that it is zoonotic, meaning it can be transferred from an animal to a human host and still remain pathogenic (3). In humans this disease cause both acute and chronic symptoms, but can be treated with antibiotics.
The B. abortus genome contains 2 circular DNA chromosomes. The first chromosome is 2,124,241 nucleotides long and codes for 2200 genes. The second chromosome is 1,162,204 nucleotides long and codes for 1156 genes. The genome has a GC content of 57%, and 81% of the genome is a coding region (10). This pathogen is different from many in that it does not contain any plasmids or genomic islands that relate to pathogenicity within its genome (5). In addition to lacking these two features, the genome also lack many other genes that code for common virulence factors including “capsules, fimbriae, exotoxins, cytolysins, resistance forms, antigenic variation, plasmids, or lysogenic phages” (1). The genes that do encode for virulence in are being examined but they are not well enough understood to say for sure what the mode of virulence is for this intracellular pathogen (5).
Cell structure and metabolism
Describe any interesting features and/or cell structures; how it gains energy; what important molecules it produces.
Brucella abortus is a parasitic bacteria, which means that it does not survive long outside the host organism. This bacterium is an intracellular pathogen that enters phagocytes, such as macrophages, in humans and in cows. It attaches to the endoplasmic reticulum of these cells (nasty bug). These smooth bacteria enter macrophages and then live in compartments of vacular space along the ER. The few cells that make it to these vacular spaces down regulate apoptosis genes within the macrophage and therefore cause the cell to resist self-death and these pathogens become resistant. These resistant bacterium are what go on to cause chronic disease in human hosts (time triggers).
In bovine species the bacteria also infects the trophoblast epithelial cells, which are the cells that provide nutrition to the embryo (time triggers). After a number of rounds of cellular replication in the trophoblast the cells lyse, causing more bacteria cells to enter the blood stream of the developing embryo (penetration). These cells in the blood stream go on to colonize the placenta and fetus in pregnant female cows, and will go on to induce abortion of the fetus (erythritol).
Brucella abortus causes a disease called brucellosis, which used to be referred to as Malta Fever because it was first discovered in soldiers who were living on the island of Malta (genome sequence). B. abortus is originally found in cattle and causes problems with fetus development and viability, but this pathogen can be passed to humans. It is uncommon in the US, most cases emerge from slaughter house workers, meat packers, or large animal veterinarians, but in the developing world the disease is much more common because their cattle herds are not vaccinated. In these cases the most common mode of transmission is through unpasteurized milk and cheese products because the bacteria is present it the milk glands of a female cow (3).
In humans the disease has both an acute and a chronic phase. The chronic phase will last as long as the host is alive without treatment. Acute symptoms include fever, chills, headache, backache, weakness, and weight loss. The chronic symptoms are usually reoccurring joint pain, fatigue, and headaches (2).
There is an antibiotic regiment for humans who come in contact with the disease that includes the antibiotics rifampin and doxycycline together (2).
Application to Biotechnology
Until 1969 the US ran a number of experiments with biological weapons. One of the bacterium used in this research was B. suis, that almost identical to B. abortus, except that its preferential host is pigs instead of cows. One of the reasons that the Brucella bacteria were targeted for development into a biological weapon was because of the length of time that it causes disease and the fact that if affects both humans and livestock. Although it does not kill human hosts, this pathogen can cause a long and lingering chronic illness that will cause a great loss in productivity of a nations workforce. Another reason this bacterium was targeted as a biological weapon is because humans consume many of the animals that it affects as food, such as pigs, cows, and goats. The final reason that this posed a great biological threat was that it can be spread through aerosols and therefore is easily dispersed, especially in an urban environment.
Enter summaries of the most recent research here--at least three required
[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.
Edited by student of Rachel Larsen and Kit Pogliano