When you experience a bacterial infection, knowing the site of infection helps doctors determine a treatment regimen. Today, clinicians figure out where these pathogens are using radiotracers – compounds with radioactive atoms that react to the X-rays and magnetic field employed by CT and MRI imaging technology. However, clinicians using these radiotracers, such as those that have radioactive fluorine (18F) or gallium citrate (88Ga), suffer from a distinction problem: they cannot distinguish live infections versus a pathogen-free inflammatory response.

Scientists at the University of California, San Francisco came up with a clever solution: synthesize a radiotracer from the building blocks of bacterial cell walls. That way, as the bacteria grow and replicate at the infection site, each live cell is incorporated with a glowing radiotracer. They proved that their radioactive carbon (11C) radiotracer integrated nicely into the bacterial cell wall in the top pathogenic bacteria for hospital settings, Pseudomonas aeruginosa and Staphlococcus aureus — including MRSA. 

But if you have an infection in your intestines, where your normal microflora live, will the radiotracer be taken up and incorporated into their cell walls rather than the pathogenic invaders? The researchers answered this question by comparing the radiotracer's location in various organs in normal mice (with normal microbiome) and microbe-free mice. They found that when the radiotracer integrated into the intestines, overall radiotracer incorporation was low, and the difference between microbe-containing and microbe-free organs was minimal. Notably, these 11C amino acids showed significant differences between live cells and dead cells, allowing clinicians to distinguish between live infection sites and sites of inflammatory responses.

Overall, the ease of creating these compounds and great incorporation efficacy into invading pathogens points to an easy translation of this radiotracer from the academic to clinical setting.