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Brucella, which causes the disease brucellosis in animals and humans, is a highly infectious bacterium of global concern. Brucellosis is not prevalent in the United States because of decades-long eradication and surveillance programs. But in less developed countries that can’t invest in the programs, brucellosis a widespread zoonosis, an animal disease that can be transmitted to humans. Brucellosis typically affects cattle, pigs, goats, sheep, and dogs by causing them to abort their fetuses. The disease also can lead to chronic fertility problems and decreased milk yields.
People can acquire Brucella infection by coming into direct contact with infected livestock or by consuming unpasteurized milk products. Brucellosis in humans is treatable with antibiotics. Because Brucella can spread easily—and only a small dose is needed to create infection—the bacterium is considered a potential agent of bioterrorism. The World Health Organization estimates there are 500,000 new human cases annually.
The scientists observed the Brucella bacterium in mouse and human immune cells moving to a newly identified protective compartment during a stage of infection where bacteria normally degrade and are removed. The protective compartment only appeared in the presence of certain combinations of proteins, which the scientists were able to change for their observations. The Brucella within these compartments successfully escaped and infected adjacent cells, thus completing its lifecycle and demonstrating its capacity to subvert normal immune defenses.
Identifying the roles of host proteins required for this bacterial subversion raises new research questions and treatment ideas for Brucella and the broad field of host-microbe interactions. For example, understanding how the bacterium signals the host cell to create the protective compartments could provide scientists with strategies for blocking this process, as could the understanding of how the compartments contribute to the release of bacteria. Immune cells use the same host defense mechanism that Brucella subverts—known as autophagy—to rid themselves of many types of pathogens, including Streptococcus, Listeria, Salmonella, and Shigella. Dr. Celli’s group plans to explore further immune system evasion connections among these pathogens to better understand the mechanisms of bacterial release.
Starr T, Child R, Wehrly T, Hansen B, Hwang S, López-Otin C, Virgin H, Celli J. Selective subversion of autophagy complexes facilitates completion of the Brucella intracellular cycle. Cell Host & Microbe. 19 January 2012.
Last Updated February 21, 2012
Last Reviewed February 21, 2012