Antibiotic resistant bacterium uses Sonar-like strategy to ’see’ enemies or prey

For the first time, scientists have found that bacteria can use a Sonar-like system to spot other cells (either normal body cells or other bacteria) and target them for destruction. Reported in the December 24 issue of Science, this finding explains how some bacteria know when to produce a toxin that makes infection more severe. It may lead to the design of new toxin inhibitors. “Blocking or interfering with a bacterium’s “detection” mechanism, should prevent toxin production and limit the severity of infection,” says Michael Gilmore, PhD, lead author of the study, and currently director of research at the Schepens Eye Research Institute and professor of ophthalmology at Harvard Medical School.

Gilmore and his team have spent years studying the bacterium known as Enterococcus faecalis, one of the leading causes of hospital-acquired infections, to find new ways to treat them. These infections are frequently resistant to many, and sometimes all, antibiotics. Tens of thousands of deaths due to antibiotic resistant infection occur each year in the US, adding an estimated $ 4 Billion to health care costs. Scientist have known since 1934 that especially harmful strains of Enterococcus produce a toxin that destroys other cells, including human cells and even other types of bacteria. They also knew that this toxin was made only under some conditions. Until Gilmore’s study, scientists were unable to explain how the Enterococcus knew when to make it.

In the Science study, Gilmore and his team found that this toxin is made whenever there is another cell type in the environment near the bacterium, such as a human blood cell. They discovered how these bacteria know when other cells are present, and respond accordingly.

In the laboratory, the team found that Enterococcus releases two substances into the environment. One substance sticks to foreign cells. The second substance reports back and tells the Enterococcus to make the toxin. If no cells are in the area, the first substance sticks to the second, preventing it from reporting back to the Enterococcus, and as a result, no toxin is made. According to Gilmore, “These bacteria are actively probing their environment for enemies or food. Based on whether or not they ’see’ other cells, they make the toxin appropriately.”

Gilmore says this discovery has several significant implications for the future. “This is a new mechanism that nature devised to ’see’ the environment, and based on that information, respond accordingly. We may be able to learn from nature and adapt a similar strategy to help the aging population cope with loss of vision,” says Gilmore.

“Secondly, this discovery will help us to develop new ways to treat infections that are resistant to antibiotics, making them less severe. Based on an understanding of how this toxin system works, we hope to develop toxin inhibitors,” says Gilmore.

The third area of interest is currently science fiction, says Gilmore. “If bacteria can see cells in the environment, maybe we can tame these bacteria and engineer this system so that it can be used to see other things in the environment, such as minerals or possibly other disease-causing bacteria,” says Gilmore.

Other members of the research team included Drs. Phillip Coburn, University of Oklahoma Health Sciences Center, Christopher Pillar, Schepens Eye Research Institute and Harvard Medical School, Wolfgang Haas, University of Rochester, and Bradley D. Jett, Oklahoma Baptist University. Dr. Michael S. Gilmore is presently Charles L. Schepens Professor of Ophthalmology, Harvard Medical School, and Marie and DeWalt Ankeny Director and Acting CEO of the Schepens Eye Research Institute.