Genetically engineered filamentous phage for bacterial detection using magnetic resonance imaging.

Detecting bacterial cells with high specificity in deep tissues is challenging. Optical probes provide specificity, but are limited by the scattering and absorption of light in biological tissues. Conversely, magnetic resonance imaging (MRI) allows unfettered access to deep tissues, but lacks contrast agents for detecting specific bacterial strains. Here, we introduce a biomolecular platform that combines both capabilities by exploiting the modularity of M13 phage to target bacteria with tunable specificity and allow deep-tissue imaging using T 1 -weighted MRI. We engineered two types of phage probes: one for detecting the phage's natural host, viz ., F-pilus expressing E. coli ; and the other for detecting a different (F-negative) bacterial target, V. cholerae . We show that these phage sensors generate 3-9-fold stronger T 1 relaxation upon recognizing target cells relative to non-target bacteria. We further establish a preliminary proof-of-concept for in vivo applications, by demonstrating that phage-labeled bacteria can be detected in mice using MRI. The framework developed in this study may have potential utility in a broad range of applications, from basic biomedical research to in situ diagnostics, which require methods to detect and track specific bacteria in the context of intact living systems.