A Microbial Biorealm page on the genus Brucella canis
Higher order taxa
Bacteria; Proteobacteria; Alphaproteobacteria; Rhizobiales; Brucellaceae; Brucella
Description and significance
Brucella canis is a gram negative obligate aerobe. Cells can be either cocci or coccibacilli and usually are not found in pairs. It has no flagella and is not motile. It has an optimum temperature of 37 degrees Celsius and an optimum pH of 6.6 to 7.4 (1). Brucella canis causes the disease brucellosis in dogs. It effects female and male dogs differently but causes sterility in both (2). B. canis causes some economic loss, because many dogs have to be euthanized in kennels due to the rapid spread of it (3). It is believed that all of the species in the genus Brucella, including B. canis, evolved from B. ovis (4).
Unlike most bacteria, Brucella canis has two chromosomes. They are both circular. However, the first chromosome is larger than the second. Chromosome I has a length of 2.1 Mbp and chromosome II has a length of 1.2 Mbp (2). It is believed that the second chromosome was originally a plasmid and that is why it is much smaller than chromosome I. Although it started out as a plasmid, it now contains genes essential to the survival of the bacteria and is considered a second chromosome (4,5,6).
Cell structure and metabolism
B. canis has an outer membrane composed of a layer of lipopolysaccharide protein, followed by a periplasmic space and then a cytoplasmic membrane which has three layers of lipoproteins (1). The exact composition of Brucella canis cell wall is unknown. Its cells contain the carbohydrates glucose, galactose, heptose and manose. B. canis has a respiratory type of metabolism, typical of obligate aerobes, and contains the enzymes catalase and oxidase. When blood is present, B. canis grows and divides faster (1).
Brucella canis is found all over the world. It has been reported in China, Japan, North America, Central America, and South America. B. canis is an obligate intracellular pathogen, so it has to be in cells to be able to reproduce (1). Its hosts are dogs and can be transmitted from dog to dog either through sexual or oral transmission (3). Brucellosis, caused by B. canis and other Brucella species, is endemic to some regions (2).
Brucella canis infects dogs, its reservoir, causing brucellosis. Brucellosis can be sexually or orally transmitted between dogs. In the female, it causes the dog to abort their young if they are pregnant. B. canis also causes endometritis, placentitis, and infertility. It also causes infertility in male dogs, as well as epididymitis and orchitis (3). Human cases have occurred through exposure to infected dogs. All the species in Brucella are considered a class III biohazard. However, B. canis is not considered a big public health risk because it rarely infects humans (4).
Recent research is trying to prove that the different species in the genus Brucella are actually different species. Since the species are currently mostly based on the host they infect, researchers are trying to prove they are in fact different species based on their genetics. The species in Brucella are all similar and the way they are divided is controversial (4,7). It was proven that there is enough differences between the Brucella species to keep them as separate species. The researchers believe that many more Brucella genomes need to be sequenced and reviewed before any changes can occur to the current Brucella taxonomy (4).
There is also research being done to find an easier way to test for brucellosis. The researchers tried latex agglutination with clear results. They took samples from infected dogs and mixed it with beads coated with antigens they got from cells of B. canis. Agglutination did form but further tests need to be done before they can say that this test is more effective than others previously used (8).
1 Krieg, Noel R., John G. Holt, and D. H. Bergey. Bergey's Manual of Systematic Bacteriology. Vol. 1. Baltimore: Williams & Wilkins, 1984. Print.
2 Wattam, Alice R., Kelly P. Williams, and Eric E. Snyder. "Analysis of Ten Brucella Genomes Reveals Evidence for Horizontal Gene Transfer despite a Preferred Intracellular Lifestyle." Journal of Bacteriology (2009). Pubmed. Web. 20 Mar. 2011. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2681906/?tool=pubmed.
3 Brower, Alexandra, Ogi Okwumabua, and Chuck Massengill. "Investigation of the Spread of Brucella Canis via the U.S. Interstate Dog Trade." International Journal of Infectious Diseases 11.5 (2007): 454-58. Science Direct. Web. 12 Mar. 2011. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B7CPT-4N55TTP-J&_user=10&_coverDate=09%2F30%2F2007&_alid=1720738320&_rdoc=1&_fmt=high&_orig=search&_origin=search&_zone=rslt_list_item&_cdi=17975&_sort=r&_st=13&_docanchor=&view=c&_ct=3&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=14e121e1cbe31163c3ae1c012a2cd60a&searchtype=a
4 Ficht, Thomas. "Brucella Taxonomy and Evolution." Future Microbiology (2010). Pubmed. Web. 30 Mar. 2011. http://www.ncbi.nlm.nih.gov/pubmed/20521932
5 “Brucella canis ATCC 23365 chromosome I, complete sequence.” Genome. Web http://www.ncbi.nlm.nih.gov/genome?Db=genome&Cmd=ShowDetailView&TermToSearch=21689
6 “Brucella canis ATCC 23365 chromosome II, complete sequence.” Genome. Web http://www.ncbi.nlm.nih.gov/genome?Db=genome&Cmd=ShowDetailView&TermToSearch=21690
7 Whatmore, Adrian M., Lorraine L Perrett, and Alastair P. MacMillan. “Characterisation of the genetic diversity of Brucella by multilocus sequencing.” (2007). Pubmed. Web. 20 Mar. http://www.ncbi.nlm.nih.gov/pubmed/17448232
8 Watarai, Masahisa., Suk Kim, and Jun Yamamoto. “A rapid agglutination assay for canine brucellosis using antigen coated beads.” Journal of Veterinary Medical Science (2007). Vol. 69. Pubmed. Web. http://www.jstage.jst.go.jp/article/jvms/69/5/69_477/_article