Eaten alive from the inside: predatory bacteria kill pathogenic bacteria from the inside out

When it comes to predators, we naturally think of large, agile, and powerful animals on the prowl. But we often don’t think about the most abundant predators on our planet, predators of the microscopic world. In the depths of the microbial universe, predatory bacteria (those that feast upon other bacteria) have emerged. These bacteria are now ubiquitous in terrestrial and marine environments. Predatory bacteria penetrate the outer membrane of bacterial prey and ingest their prized nutrients, killing the prey.

Bdellovibrio life cycle. Image credit: Willis et al., 2016.

Though it may seem trivial at first glance, scientists have been studying these microscopic predator-prey relationships for their powerful therapeutic potential. In a recently published paper in Current Biology, scientists from Imperial College London and Nottingham University Medical School describe their recent work on predatory bacteria. They hope predatory bacteria may one day be used to treat pathogenic bacterial infections. Bacterial infections are becoming more resistant to available antibiotics, making treatment difficult and even impossible at times. Many fear that the antibiotic apocalypse is approaching. Thus, researchers are looking for more creative strategies to overcome potentially lethal infections.

The UK-based scientists studied Bdellovibrio bactriovorus predation on Shigella flexneri bacterial cells in the zebrafish larvae. Shigella causes foodborne illnesses in millions of people yearly and is resistant to many antibiotics. The group used zebrafish larvae because it is transparent allowing them to easily see the bacteria inside. When injected in the larvae alone, Shigella killed about 75 percent of the larvae after three days. In contrast, when the larvae were injected with both Shigella and Bdellovibrio, only about 40 percent of the larvae met their demise.

But is this increased survival due to Bdellovibrio predation on the Shigella cells? The researchers engineered each type of bacterium to produce different fluorescent colors. Bdellovibrio cells were red while Shigella glowed green. Inside live larvae, the scientists could see Bdellovibrio invading and replicating within Shigella cells. At the same time, Shigella cell numbers decreased. The scientists believe that even though Bdellovibrio might not completely clear the infection, it reduces the infection to a more manageable state. That way, the immune system can take over and eliminate the remaining Shigella cells.

Observing Bdellovibrio (red) and Shigella (green) interaction in the zebrafish. Image credit: Willis et al., 2016.

The researchers hope that predatory bacteria can one day be used to treat wound infections where injection of the predatory bacteria into the wound can clear the infection locally. On a broader scale, such a predator-prey treatment model may potentially be used to treat infections caused by a multitude of infamous bacteria such as methicillin-resistant Staphylococcus aureas (MRSA) and carbapenem resistant Enterobacteriaceae (CRE).

We are approaching the “post antibiotic era,” a time where once treatable infections are no longer treatable. Bacteria are becoming more and more resistant to drugs available today. Once treatable infections will become lethal again and surgeries may come with a greater risk of bacterial infection. There is an arms race between researchers and microbes, and the microbes might be winning. Yes, we can synthesize new antibiotics, but it is likely that pathogens will develop resistance rendering these antibiotics obsolete. In a time when antibiotics have failed us, unorthodox solutions such as these “living antibiotics” demand our attention.

CC BY-NC-ND 4.0 Eaten alive from the inside: predatory bacteria kill pathogenic bacteria from the inside out by Jennifer Tsang is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

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