Cannibalistic Bacteria Show Potential As ‘Living Antibiotic’

Predatory bacteria — bugs that eat other bugs of their kind — could potentially be a new weapon in the fight against superbugs.

Scientists from the Imperial College London and the University of Nottingham report promising findings in a study performed to assess whether a predatory bacterium can be effective against drug-resistant infections. In a study published in Current Biology, researchers in England injected zebrafish larvae with Bdellovibrio bacteriovorus, to see if Bdellovibrio had a pathogenic effect on the larvae, and whether the bacteria could survive long enough to prey on a predatory infection. Bdellovibrio is a small, curved, and highly motile Gram-negative bacteria approximately that can be found in soil, sewage, and other terrestrial and aquatic habitats. It has been observed to specifically attack Gram-negative bacteria making it an excellent candidate as a biocontrol agent (“living antibiotic”) in environmental as well as medical microbiological settings since it has not been shown to affect humans. Bdellovibrio preys upon a wide variety of other gram-negative bacteria, including Escherichia coli, Salmonella, and Aquaspirillum serpens.

Bdellovibrios were discovered by Heinz Stolp and Heinz Petzhold in 1962 while attempting to isolate bacteriophage of the phytopathogen Pseudomonas syringaepv from soil suspension.

The researchers found that the bacteria had no toxic effect on the larvae, and that they are able to survive for long periods but need prey bacteria to replicate and act therapeutically before they can be naturally cleared by the immune system. Once the researchers determined that the Bdellovibrio had no negative effect, they injected zebrafish larvae with a lethal dose of drug-resistant Shigella flexneri, a bacterium that causes severe and sometimes fatal diarrhea. (Globally, Shigella infections cause over 160 million infections and 1 million deaths). The investigators then injected Bdellovibrio into the site of infection to determine its efficacy against the pathogen. Larvae with Bdellovibrio were able to control the replication of Shigella significantly better than larvae that did not receive the bacterium.

Bdellovibrio is also able to reduce pathogen load in immunocompromised zebrafish larvae that have been depleted of white blood cells. Survival is significantly greater in immune-competent zebrafish, showing that Bdellovibrio’s maximum benefit comes from its ability to work cooperatively with the host’s own immune system. Inside the translucent zebrafish larvae, the scientists could see Bdellovibrio working together with leukocytes (white blood cells), the cells of the immune system that goes into action whenever a pathogen invades the body.

In an earlier study done at the Rutgers New Jersey Medical School, investigators showed that predatory bacteria can kill pneumonia in a rat m odel. These studies provide evidence that predatory bacteria can be used as a therapeutic agent.

It has been known for a while now that bacterial predators carry out their predation by attaching to the outside of host cells or penetrating into the host cell to live inside it. Bacterial predation by bacteria is a topic with lots of unknown knowns and unknown unknowns most especially regarding intracellular communication. To use them as potential living antibiotics, it is important to understand the signals used by bacterial predators to kill other bacteria.