The staph bacteria are located via a light-emitting molecule (green), which is released when a bacterial enzyme (in orange) slices and separates the probe (shown in blue); © University of Iowa/McNamara Lab
Researchers at the University of Iowa have created a noninvasive chemical probe that detects a common species of staph bacteria in the body.
The probe ingeniously takes advantage of staph's propensity to slash and tear at DNA, activating a beacon of sorts that lets doctors know where the bacteria are wreaking havoc.
"We have come up with a new way to detect staph bacteria that takes less time than current diagnostic approaches," says James McNamara, assistant professor in internal medicine at the UI. "It builds on technology that has been around a long time, but with an important twist that allows our probe to be more specific and to last longer."
The UI-developed probe targets Staphylococcus aureus, a species of staph bacteria common in hospitals and found in the general public as well. The bacteria causes skin infections, can spread to the joints and bones and can be fatal, particularly to those with weakened immune systems.
"Every year in the U.S., half a million people become infected by S. aureus bacteria, and 20,000 of those who become infected die," adds Frank Hernandez, a post-doctoral researcher at the UI. "We believe that we are significantly improving the actual methods for detecting bacteria with a simple approach, which we expect to be cheap, fast and reliable."
What makes staph especially troublesome is doctors do not know the bacteria are in the body until they get the biopsy results, which usually takes days. "They are flying blind, so to speak," McNamara says. "It is the state of medicine at this time." The UI team created a synthetic probe with two unique features. On one end is a molecule that gives off light under certain conditions. On the other end is another molecule that blocks that light. In other words, the particle, as designed, cancels itself out, leaving itself undetectable inside the body.
This is important due to what staph bacteria will do to the particle. In tests, nucleases (or enzymes) produced by the staph bacteria cleave the particles, like a warrior wielding a sword. Why it does this is unclear, but scientists believe it is a clever way for staph, which cannot move by itself, to spread beyond the molasses-like environment created when DNA leaks from infected, dying cells. In any event, when staph cleaves the probe, it separates the light-emitting molecule from the light-blocking molecule, which then drifts too far away to block light. And, so with the right equipment, doctors would be able to see the light-emitting molecules and know that staph are raging there.
Outfitting such particles is not altogether new, but McNamara and his colleagues produced a probe that lasts longer - by several hours longer for certain types. "We designed a tracking system that specifically identifies bacterial body localization in less than one hour," says Hernandez, who for years has been working on probes to detect harmful bacteria.
Just as important, the UI probe has been chemically modified so that it is shredded only by the staph bacteria's nuclease and not by a nuclease secreted by normal, healthy cells. The team further tested the probe in mice and human serum and report that it performed as expected. "That is the central idea, the underlying concept of our approach," says McNamara. "If the probe gets cleaved by serum nucleases, then our probe would be lit up all over the bloodstream. But since it is split only by staph nucleases, then we can pinpoint where the staph bacteria are active."
MEDICA.de; Source: University of Iowa