Simple, versatile genetic ‘toolkit’ releases a glowing label to bacteria for its easy observation & identification

Article Source: Beth Israel Deaconess Medical Center

Abstract: Making use of a new methodology, researchers have investigated mechanisms of infection and provided new clues into how different bacteria cooperate with each other to cause disease. The new tool has allowed researchers to study Brucella species, which cause a potentially debilitating infectious disease in humans and cattle

Complete report:

Brucellosis is an infectious disease of livestock caused by the Bacterial genus Brucella. The disease generally spreads when a person, mostly a farm worker comes in contact with the animal or animal product infected with the bacteria. Easy to spread and hard to detect, the bacteria that cause the illness, Brucella species, are considered a significant health threat and potential bioterror weapons in various parts of the world. It has also been reported that Brucella species are so dangerous to handle that the research on this important disease-causing agent, or pathogen, has lagged behind that of other infectious diseases.

Making use of an innovative method to study the infectious process, investigators at Beth Israel Deaconess Medical Center (BIDMC) have established a safer way to study Brucella. In a previous test of the model, the research team found an astonishing and previously undocumented interaction during the infectious process. They also reported a presence of another pathogen that improves the infectious potential of Brucella. The research has been published in the journal Infection and Immunity.

In the context of this research, James Kirby, MD, Director of the Clinical Microbiology Laboratory at BIDMC and Associate Professor of Pathology at Harvard Medical School said, “Our toolkit is simple, versatile and applicable to any type of pathogen.”  He further added that “This will be something that will help the scientific community study infectious disease more efficiently going forward because bacterial strains of interest can be constructed so easily, saving a lot of time and effort.”

Kirby and co-author Yoon-Suk Kang, PhD, a post-doctoral fellow in Kirby’s lab used their technique to engineer a special strain of Brucella designed to emit colored light so they could more easily observe it infect host cells in the lab.

There are several different strains of Brucella bacteria. Some are seen in cows while others occur in dogs, pigs, sheep, goats, and camels. However, there are majorly four types of Brucella bacteria that cause the majority of brucellosis infections in humans. They are studied in designated biosafety level 3 laboratories due to their potential to cause life-threatening and debilitating infections.

But Kirby & Kang, used another Brucella species, B. neotomae that infects only rodents, to check if it had some similarity with its more dangerous relatives to serve as a safer-to-handle investigational model for all Brucella species.

While observing their custom strain, Kirby and Kang witnessed an unparalleled interaction between B. neotomae and Legionella pneumophila, an infectious agent known for causing Legionnaires’ disease in humans.

Not only it emitted light but the genetically-altered strain of B. neotomae was also designed to lack the physical structure it needs – a molecular syringe – to attack host cells. These engineered bacteria were not able to grow and multiply inside the host cell on their own. However, when the host cells were co-infected with this strain of Brucella and L. pneumophila which was also engineered to emit colored light, at the same time, the harmless B. neotomae thrived.

Kirby also noted that this de-fanged version of B. neotomae grew better in the presence of L. pneumophila than virulent Brucella normally does without it.

Based on the above observations, Kirby said, “Legionella provided all the factors Brucella needs for infection.”  He added, “It was completely out of the blue. It highlights that pathogens can interact in unexpected ways. The whole is greater than the sum of its parts.”

The concept of creation of the light-emitting bacteria by introducing genes for fluorescent proteins into their genomes is not new, but the genetic “tool kit” developed by Kirby and Kang greatly streamline the process by using easy-to-manipulate genes called transposons –also called jumping genes – to quickly and safely label the bacteria.

The researchers’ technique avoids one significant drawback to traditional means of labeling bacteria for study. Generally, scientists isolate bacteria for study by engineering drug-resistant strains and growing them in a petri dish infused with antibiotics, which kills any bacteria not required in the experiment.

“That’s something we’ve been concerned about,” said Kirby, whose lab also seeks to develop novel antimicrobials as drug-resistant bacteria become an increasing problem globally. “We don’t want to make bacteria more resistant to antibiotics. Our toolkit won’t confer resistance to anything that might be used in human therapy.”

Journal Reference:

Yoon-Suk Kang, James E. Kirby. Promotion and Rescue of Intracellular Brucella neotomae Replication during Coinfection with Legionella pneumophilaInfection and Immunity, 2017; 85 (5): e00991-16 DOI: 10.1128/IAI.00991-16