The bacterium responsible for strep throat, scarlet fever and other disorders appears to use a single wasplike “stinger” to spread infection, according to University microbiologists.
Researchers studying the surface of Streptococcus pyogenes, also known as Strep A, had expected to find a disordered jumble of several pumps for spraying compounds onto cells targeted for infection. Instead, they found a single dedicated stinger — a feature Strep A may share with other bacteria that could provide an easier target for new drugs designed to treat infections.
“It’s certainly a long time down the road, but this gives us new ways to think about how strep and other bacteria might one day be stopped,” said Michael G. Caparon, Ph.D., professor of molecular microbiology and the study’s lead investigator.
Strep A is one of the most common human pathogens. Epidemiologists estimate that at any given time 5 percent to 15 percent of humans carry asymptomatic Strep A. Drug resistance in strep has been growing for more than a decade.
On the basis of Strep A’s outer membrane, microbiologists classify it as a Gram-positive bacteria. Such bacteria only have one outer membrane, but Gram-negative bacteria have two outer membranes separated by a small space. That space between the inner and outer membranes serves as a prep room for proteins and other agents that Gram-negative bacteria secrete to infect host cells.
Many proteins won’t function properly unless they have folded into a particular configuration, and scientists believe the space between the two membranes provides Gram-negative bacteria with a place to ensure the right folding and other preparatory steps take place.
Caparon was curious about how Gram-positive bacteria like Strep A prepare their infectious agents without this airlock-like space between membranes.
“Strep A is known to secrete more than 30 different substances as a part of its infectious processes,” he said. “We wanted to know how does Strep A emits these agents?”
Most microbiological evidence suggested bacteria have little structural organization beyond the shape of their cells. But a few studies, including some from Caparon’s lab, recently hinted that bacteria might be more organized than scientists suspected.
Caparon and graduate student Jason Rosch used modified antibodies to tag an infectious agent secreted by Strep A. They then took micrographs of the bacteria. The antibodies consistently showed up at a single focal point where the cell was secreting the infectious agent.
After follow-up tests confirmed what they had observed, Caparon decided to name the new structure that secretes infectious agents “exportal,” a combination of export and portal.
“We’d like to now look at how the cell actually puts this together,” Caparon said. “If we can identify the factors that are actually involved in structurally putting the exportal together, those may be the most interesting points of intervention for devising new drug treatments.”
Caparon also wants to test other Gram-positive bacteria to learn if they have exportals.