Immune system protein starves 'staph' bacteria

Findings point to new way to treat infections

One of the ways we defend ourselves against bacterial foes is to “hide” their food, particularly the metals they crave. A multi-disciplinary team led by Vanderbilt University investigators has now discovered that a protein inside certain immune system cells blocks the growth of “staph” bacteria by sopping up manganese and zinc.

The findings, reported Feb. 15 in Science, support the notion that binding metals – to starve bacteria – is a viable therapeutic option for treating localized bacterial infections. New treatment strategies are urgently needed to combat the surging number of infections and deaths caused by antibiotic-resistant forms of Staphylococcus aureus (staph), such as MRSA.

If recent estimates are accurate, the number of deaths caused by MRSA exceeds the number of deaths attributable to HIV/AIDS in the United States.

“Staph is arguably the most important bacterial pathogen impacting the public health of Americans,” said Eric Skaar, Ph.D., assistant professor of Microbiology and Immunology and senior author of the study.

Staph is the leading cause of pus-forming skin and soft tissue infections, the leading cause of infectious heart disease, the number one hospital-acquired infection, and one of four leading causes of food-borne illness.

“And it seems as if complete and total antibiotic resistance of the organism is inevitable at this point,” Skaar said.

The dire outlook motivates Skaar and his colleagues in their search for new antibiotic targets.

Skaar and Brian Corbin, Ph.D., postdoctoral fellow and lead author of the report in Science, reasoned that proteins present at the site of a staph infection might be important to the battle between the bug and the immune system, and might therefore make good targets for therapeutics. They took advantage of the fact that staph forms abscesses – pimple-like infected areas – in internal organs like the liver.

“Because we can tell exactly where the infection is, we can look for proteins that are present only at the site of infection,” Skaar said.

Using sophisticated technology called “imaging mass spectrometry,” the investigators identified dozens of proteins specifically expressed in staph abscesses in mice. They decided to focus on one that was particularly abundant.