Identifying staph with a beacon, not a biopsy

Researchers at the University of Iowa (UI) have created a probe that can detect a common strain of staph bacteria (Staphylococcus aureus) in the body. Their method has been published in the journal Nature Medicine.

S. aureus causes skin infections, can spread to the joints and bones and can be fatal, particularly to those with weakened immune systems. According to the paper’s first author, Frank Hernandez, “Every year in the US, half a million people become infected by S. aureus bacteria, and 20,000 of those who become infected die.”

The current diagnostic method requires doctors to take a biopsy, send it off for analysis and wait days for the results, all while unable to begin treatment. The UI team, on the other hand, developed a molecular imaging approach which utilises a synthetic probe.

On one end of the probe is a molecule that gives off light under certain conditions. On the other end is another molecule that blocks that light. The particle thus leaves itself undetectable inside the body - except in the presence of staph.

The staph bacteria are located via a light-emitting molecule (green), which is released when a bacterial enzyme (orange) slices and separates the probe (blue). Credit: McNamara lab, University of Iowa.

Nucleases produced by staph bacteria cleave and slash at the particles. When staph tears the probe, it separates the light-emitting molecule from the light-blocking molecule. So, with the right equipment, doctors would be able to see the light-emitting molecules and thus identify the presence of staph.

James McNamara, corresponding author of the paper, noted that the probe has been chemically modified so that it’s shredded only by the staph bacteria’s nuclease and not by a nuclease secreted by normal, healthy cells.

“If the probe gets cleaved by serum nucleases, then our probe would be lit up all over the bloodstream,” he said. “But since it’s split only by staph nucleases, then we can pinpoint where the staph bacteria are active.”

McNamara says this technology has been around for a long time, but the new probe lasts several hours longer than previous efforts. Yet it is still very quick, added Hernandez, identifying bacterial body localisation in less than an hour.

McNamara said the team plans to refine the probe so it can be detected deeper in the body and to test its performance with catheter infections.

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