Detecting Bacteria in Their Mammalian Hosts Using Metabolism-Targeted [¹³C]CO₂ Breath Testing

Infectious diseases are a major cause of morbidity and mortality worldwide. With the increasing frequency of antibiotic resistance, efficient and noninvasive diagnostic methods are more important than ever. In this report, we interrogate the use of several intravenously administered, bacteria-specific, ¹³C-enriched metabolites whose conversion to [¹³C]-CO₂ can be detected via a portable and inexpensive method, namely nondispersive infrared (NDIR) spectroscopy. The enriched metabolites [U-¹³C]-maltose, [U-¹³C]-maltotriose, d-[U-¹³C]-mannitol, and l-[U-¹³C]-arabinose were metabolized to [¹³C]-CO₂ by several pathogens in vitro, while showing minimal [¹³C]-CO₂ production in uninfected mice. We further demonstrated that myositis, bacteremia, pneumonia, and osteomyelitis could be detected in vivo using one or more ¹³C-enriched metabolites. Additionally, in a model of Escherichia coli myositis, [¹³C]-CO₂ production correlated with bacterial burden following ceftriaxone therapy, showing that exhaled [¹³C]-CO₂ could be employed to monitor antimicrobial efficacy. Finally, [¹³C]-CO₂ production by Staphylococcus aureus clinical isolates treated with [U-¹³C]-maltose was correlated with the performance of its cognate PET tracer [2-¹⁸F]-maltose, suggesting that [¹³C]-CO₂ breath testing could predict the performance of pathogen-targeted positron emission tomography (PET) tracers in vivo. [¹³C]-CO₂ breath testing using an expanded metabolite toolbox and on-site detection tools represents a unique and complementary method to identify bacterial infection in clinical practice.