Bacterial association with metals enables in vivo tracking of microbiota using magnetic resonance imaging
Bacteria constitute a significant part of the biomass of the human microbiota, but their interactions are complex and difficult to replicate outside the host. Exploiting the superior resolution of magnetic resonance imaging (MRI) to examine signal parameters of selected human isolates may allow tracking of their dispersion throughout the body. We investigated longitudinal and transverse MRI relaxation rates and found significant differences between several bacterial strains. Common commensal strains of lactobacilli display notably high MRI relaxation rates, partially explained by outstanding cellular manganese content, while other species contain more iron than manganese. Lactobacillus crispatus show particularly high values, 4-fold greater than any other species; over 10-fold greater signal than relevant tissue background; and a linear relationship between relaxation rate and fraction of live cells. Different bacterial strains have detectable, repeatable MRI relaxation rates that in future may enable tracking of their persistence in the human body for enhanced molecular imaging. IMPORTANCE To understand how spatial and temporal distribution of microbiota impact human health, dynamic tools for monitoring microbiota landscapes inside the host are needed. Particularly when considering the complexity of the gastrointestinal tract and the microbiota that dwell within, tools for monitoring deep segments of the gut non-invasively are required. Medical imaging provides solutions that enable the study of microorganisms in their preferred niche regardless of health status. To bootstrap this technology, we investigated the magnetic resonance imaging (MRI) properties of bacterial isolates and showed that outstanding signal detection is an inherent property of several strains. Among these, we showed that bacteria relying on manganese metabolism have an MRI characteristic that is distinct from mammalian cells. Our findings will lead to direct and safe imaging of bacteria; influence how we monitor both infection and gut health; and help direct the use of antibiotics to curtail the growing threat of antibiotic resistance.