The development of bacterial magnetic resonance imaging for microbiota analyses
Abstract
Current microbial analyses to assess either the commensal microbiota or microorganism infection and disease typically require ex vivo techniques that risk contamination and are not undertaken in real time. The possibilities for employing imaging techniques in the microbiology field is becoming more prominent as studies expand on the use of positron emission tomography, ultrasound and numerous microscopy techniques. However, magnetic resonance imaging (MRI), a non-invasive in vivo modality that can produce real-time results is falling behind. Here, we examined the feasibility of detecting bacteria using clinical field strength MRI. Commensal, probiotic and uropathogenic Escherichia coli were scanned by 3 Tesla MRI where signal was related to the number of colony-forming units as well as total cellular iron and manganese content as determined by mass spectrometry. Various microbes commonly found in the human gut and urogenital tract were also assessed by MRI. Lactobacillus spp. displayed significantly higher transverse relaxation rates than other species, despite their low iron usage, potentially due to high manganese content. High MR relaxivity may enable detection of lactobacilli amidst host tissues, therefore, we assessed the potential to distinguish the MR signatures of two distinct cell types within mixed samples. With clinical field strength MRI, we were able to detect as few as ~26 x 106 colony-forming units of Lactobacillus crispatus ATCC33820 per mm3. In the future, MRI may allow for non-invasive evaluation of health or dysbiosis in the human microbiota as well as potential applications in tracking the dispersion and persistence of bacteria in broad applications from probiotic use, infection to tumour tracking.