The increasing prevalence of bacteria resistant to antibiotic drugs is largely blamed on the over prescription and use of such drugs in humans and animals, leading to the evolution of so-called "superbugs." A new antibiotic "smart bomb" that can target specific strains of bacteria could provide the next-generation antibiotic drugs needed to stave off the threat of antibiotic-resistant bacteria.

Developed by researchers at North Carolina State University, the new technique offers the potential of a powerful new weapon in the fight against multi-drug resistant bacteria. And unlike conventional antibiotic drugs that kill both good and bad bacteria, the new approach targets and kills specific strains of bacteria, while leaving the beneficial bacteria untouched – hence the "smart bomb" tag.

As a part of their immune system, many bacteria have a system called CRISPR-Cas. When under attack from invaders, such as viruses, the CRISPR-Cas system creates small strands of RNA called CRISPR RNAs that match the specific DNA sequences of the invader. When these CRISPR RNAs find a match, they release proteins that sever the invader's DNA, thereby eliminating the infection.

By designing CRISPR RNAs that target the bacteria's own DNA, the NC State researchers have turned the bacteria's own immune system on itself, so they essentially commit suicide.

"In lab testing, we found that this approach removes the targeted bacteria," said Dr. Chase Beisel, an assistant professor of chemical and biomolecular engineering at NC State. "We’re still trying to understand precisely how severing the DNA leads to elimination of the bacteria. However, we’re encouraged by the ease in specifically targeting different bacteria and the potency of elimination."

In controlled cultures and in the presence of different combinations of bacteria, the team was able to eliminate Salmonella bacteria, without affecting good bacteria. They also demonstrated the ability to eliminate one strain of a species, while another strain of the same species that shared 99 percent of the same DNA remained unaffected.

"By targeting specific DNA strands through the CRISPR-Cas system, we’re able to bypass the mechanisms underlying the many examples of antibiotic resistance," added Dr. Beisel.

The researchers are now working to develop CRISPR RNA delivery methods that could be effectively implemented in clinical settings.

The paper detailing the work is published online in the journal mBio.