Novel Bacterial Detectors

Bacteria blues: Bacteria collected in the bottom of the tube on the right have been labeled with a blue imaging agent.
Credit: Niren Murthy

Biomedicine

A Light Switch for Bacterial Infections

A new contrast agent could detect bacteria on medical implants, and help doctors decide how to treat infection.

• Monday, July 25, 2011
• By Katherine Bourzac

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A new contrast agent that targets microbes can be used to illuminate bacterial infections in living animals. It could ultimately enable doctors to safely spare more of a limb during amputations.
It's usually clear when a patient has a bacterial infection and needs to be treated with antibiotics, says Jason Bowling, director of epidemiology at the University of Texas Health Science Center at San Antonio, who was not involved with developing the imaging agent. But sometimes an infection is more difficult to diagnose. For example, it can be difficult to tell when a patient who has pain at the site of a hip or knee replacement has an infection. This sometimes leads doctors to prescribe antibiotics when they aren't necessary.
An imaging scan capable of detecting bacteria would quickly answer the question, sparing uninfected patients from unnecessary antibiotics or even from surgery to remove the implant. Where there is an infection and the implant is removed, imaging could help ensure that no new hardware is implanted until the infection has been completely cleared.
It's challenging to image infections because many of the molecules used to target bacteria can accumulate in tissue that is merely inflamed rather than infected, says Niren Murthy, professor of biomedical engineering at Georgia Tech, who was involved with developing the new agent. The new imaging agent is taken up by bacteria in large quantities, but it won't stick around in other tissue. "We had to find something very specific to bacteria," he says.
Murthy's group stole a trick from a group of viruses that gets its genome inside bacteria by attaching it to a bacterial food source, a carbohydrate called maltohexaose. Bacteria have proteins on their cell walls whose job is to bring maltohexaose inside the cell, and this happens even if that maltohexaose is attached to an imaging agent. Animal cells don't have these proteins, so they don't take up the contrast agen