The University of Illinois researchers said they discovered macrophages -- the immune cells that engulf and kill bacteria -- direct their attack on targets outside the bacteria's membrane-bound cytoplasm.
University of Illinois Graduate student Maureen Craig and Professor James Slauch said they discovered macrophages kill bacteria with reactive oxygen species, or ROS, which are substances toxic to the cell.
"It's been assumed that reactive oxygen species kill the bacteria by going into the cytoplasm and causing DNA damage," Slauch said.
Craig and Slauch examined the action of enzymes that neutralize an important ROS in a bacteria called Salmonella typhimurium. The researchers found the bacteria were profoundly weakened when a genetic mutation disabled production of the protective enzyme outside the bacteria's cytoplasm.
"We conclude … the most sensitive target of ROS in the macrophages lies outside the cytoplasm," Slauch said. "We don't know what that target is, but it's clearly not in the cytoplasm."
The study appears in the online journal PLoS One.