Researchers design viruses to kill deadly pathogens

Researchers at Northwestern University have managed to convince a deadly pathogen to destroy itself from the inside.

In a new study, researchers modified the DNA of a bacteriophage or “phage,” a type of virus that infects and replicates inside bacteria. Next, the research team inserted the DNA into Pseudomonas aeruginosa (P. aeruginosa), a deadly bacteria that is also highly resistant to antibiotics. Once inside the bacteria, the DNA bypassed the pathogen’s defense mechanisms to assemble into virions, which passed through the bacteria’s cell to kill it.

Building on a growing interest in “phage therapies,” the experimental work represents a crucial step toward engineering viruses as new treatments to kill antibiotic-resistant bacteria. It also reveals vital information about the inner workings of phages, an understudied area of ​​biology.

The study, “A synthetic biology approach to assemble and reboot clinically relevant Pseudomonas aeruginosa tailed phages,” was published in the journal Microbiology spectrum.

“Antimicrobial resistance is sometimes referred to as a ‘silent pandemic,’” said Northwestern’s Erica Hartmann, who led the work.

“The number of infections and deaths from infections is increasing around the world. It’s a huge problem. Phage therapy has emerged as an untapped alternative to our reliance on antimicrobials. But, at In many ways, phages are the “final frontier” of microbiology. We don’t know much about them. The more we learn about how phages work, the more we can design more effective therapies. Our project is to “state of the art in that we learn the biology of phages in real time as we engineer them.”

An indoor microbiologist, Hartmann is an associate professor of civil and environmental engineering at Northwestern’s McCormick School of Engineering and a member of the Center for Synthetic Biology.

Desperate need for alternatives to antibiotics

Combined with increasing use of antimicrobials, the rise of antibacterial resistance poses an urgent and growing threat to the global population. According to the Centers for Disease Control and Prevention (CDC), nearly 3 million antimicrobial-resistant infections occur each year in the United States alone, resulting in the deaths of more than 35,000 people.

The growing crisis has prompted researchers to look for alternatives to antibiotics, which are continually losing their effectiveness. In recent years, researchers have begun to explore phage therapies. But even though there are billions of phages, scientists know very little about them.

“For every bacterium that exists, there are dozens of phages,” Hartmann said. “So there are an astronomical number of phages on Earth, but we only understand a handful of them. We haven’t necessarily had the motivation to really study them. Now the motivation is there, and we’re increasing the number of phages. phages.” tools that we must devote to their study.

Treatment without side effects

To explore potential phage therapies, researchers identify or modify an existing virus to selectively target a bacterial infection without disrupting the rest of the body. Ideally, scientists could one day tailor a phage therapy to infect a specific bacteria and design “à la carte” therapies with precise traits and characteristics to treat individual infections.

“The powerful thing about phages is that they can be very specific, unlike antibiotics,” Hartmann said. “If you take an antibiotic for a sinus infection, for example, it disrupts your entire gastrointestinal tract. Phage therapy can be designed to affect just the infection.”

While other researchers have studied phage therapies, almost all of those studied have focused on using phages to infect Escherichia coli. Hartmann, however, decided to focus on P. aeruginosa, one of the five deadliest human pathogens. Particularly dangerous for people with weakened immune systems, P. aeruginosa is a leading cause of hospital infections, often infecting patients with burns or surgical wounds as well as the lungs of people with cystic fibrosis.

“This is one of the highest priority multidrug-resistant pathogens that a lot of people are concerned about,” Hartmann said. “It is extremely resistant to drugs, so there is an urgent need to develop alternative therapies.”

Mimic the infection, bypass the defenses

In the study, Hartmann and his team started with the bacteria P. aeruginosa and purified DNA from several phages. Next, they used electroporation – a technique that delivers short, high-voltage electrical pulses – to punch temporary holes in the bacteria’s outer cell. Through these holes, the phage DNA entered the bacteria to mimic the infection process.

In some cases, the bacteria recognized the DNA as a foreign body and shredded it to protect itself. But after using synthetic biology to optimize the process, Hartmann’s team was able to neutralize the bacteria’s antiviral self-defense mechanisms. In these cases, the DNA successfully carried information into the cell, resulting in virions that killed the bacteria.

“Where we have succeeded, you can see dark spots on the bacteria,” Hartmann said. “This is where the viruses come out of the cells and kill all the bacteria.”

After this success, Hartmann’s team introduced DNA from two other phages naturally incapable of infecting their strain of P. aeruginosa. Once again, the process worked.

Making phages in a cell

Not only did the phage kill the bacteria, but the bacteria also ejected billions of additional phages. These phages can then be used to kill other bacteria, such as those that cause infection.

Next, Hartmann plans to continue modifying the phages’ DNA to optimize potential therapies. For now, his team is studying phages expelled from P. aeruginosa.

“This is an important part of making phage therapies,” she said. “We can study our phages to decide which ones to develop and eventually mass produce them for therapeutic purposes.”