The bacteria that cause brucellosis need to steal food from their hosts’ bodies to survive, and Washington State University researchers may have identified an accomplice: a protein in the host cell.
Brucellosis is one of the world’s most widespread zoonotic diseases, meaning it can transfer from animals to humans, though it is rare in the United States. Its symptoms include fever, weight loss, and joint pain, and in severe cases, it can cause central nervous system and heart inflammation. While antibiotics can treat brucellosis, relapses are common, and due to the threat of antibiotic resistance, researchers are looking for new, affordable control strategies.
According to the study published in The EMBO Journal, a recently characterized protein – BspF – appears to reorganize a pathway that is believed to provide nutrients required for the bacteria to grow inside the host cell. The finding could lead to interventions to mitigate the bacterial growth.
“Once inside the cell the bacteria need to acquire food from somewhere, and the cell is not a supermarket; everything is hidden in certain ways,” said Professor Jean Celli of WSU’s Paul G. Allen School for Global Health in the College of Veterinary Medicine. “We believe this particular protein is manipulating specific cell functions to steal nutrients required for the bacteria to grow and multiply.”
Brucellosis, also known as Mediterranean fever, is caused by the bacterium Brucella abortus. Endemic in Africa, Asia, Europe, and South America, brucellosis can be spread through unpasteurized dairy products and close animal contact, cattle serving as the primary host.
Much of the research the past three years was led by Elizabeth Borghesan, a graduate student in the Celli lab, but the work on this protein was a nine-year endeavor.
In WSU’s biosafety level 3 laboratory, Borghesan took immune cells, also known as macrophages, from live mice. Then, to explore the function of different proteins, she cultured those cells and infected them with different strains of Brucella that were missing specific proteins. A strain of Brucella missing no proteins served as a control.
Using a reliable method to delete genes, Borghesan and her colleagues directly removed the gene coding for the protein and used fluorescence microscopy to determine the absent protein’s function.
Without the protein, bacterial growth was significantly slowed.
“When we removed the protein, we initially saw that the bacteria were unable to replicate as well as when the protein was present. Growth was not completely inhibited, but it definitely grew slower or was unable to grow as well as the control,” Borghesan said.
The protein is the second of some 12 bacterial proteins that have been discovered in the Celli lab. The first protein was found to be essential in creating a “nest” for the bacterium once inside the cell.
Celli, who has dedicated his entire career to Brucella, wishes he could see all the known proteins’ functions characterized in his lifetime.
He said if the functions of the different proteins were known, then researchers could genetically target a select few and disrupt the bacterium’s lifecycle inside the cell.
“The bacterium needs the cell to replicate, but if you can prevent the bacteria from using the cell, then you have a way to counteract and prevent that replication,” Celli said. “And if you can do that, you should be able to mitigate the disease.”