Some time ago, researchers at Massachusetts General developed a microfluidic device that uses magnetically tagged particles coupled with antibodies to detect cancer. They’ve been attempting to transfer the technology to identifying bacterial strains in body fluid samples, but finding matching antibodies has proven a challenge.
To overcome this, the team targeted the DNA directly, developing sequences of nucleic acids (AGTC) that couple to specific bacterial strains. Nuclear magnetic resonance is then used to spot these paired particles within a sample. The team showed that it’s practical to use the system to diagnose specific strains of tuberculosis within only a few hours, considerably faster than other easy to use techniques.
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The Nature Nanotechnology paper, being issued online today, describes a similar system using ribosomal RNA (rRNA) – already in use as a bacterial biomarker – as a target for nanoparticle labeling. The investigators developed both a universal nucleic acid probe that detects an rRNA region common to many bacterial species and a set of probes that target sequences specific to 13 clinically important pathogens, including Streptococcus pneumoniae, Escherichia coli and methicillin-resistantStaphylococcus aureus (MRSA).
The device was sensitive enough to detect as few as one or two bacteria in a 10 ml blood sample and to accurately estimate bacterial load. Testing the system on blood samples from patients with known infections accurately identified the particular bacterial species in less than two hours and also detected two species that had not been identified with standard culture techniques.
While both systems require further development to incorporate all steps into sealed, stand-alone devices, reducing the risk of contamination, Weissleder notes that the small size and ease of use of these devices make them ideal for use in developing countries. “The magnetic interactions that pathogen detection is based on are very reliable, regardless of the quality of the sample, meaning that extensive purification – which would be difficult in resource-limited setting – is not necessary. The ability to diagnose TB in a matter of hours could allow testing and treatment decisions within the same clinic visit, which can be crucial to controlling the spread of TB in developing countries.”
Nature Communications: Magnetic barcode assay for genetic detection of pathogens
Nature Nanotechnology: A magneto-DNA nanoparticle system for rapid detection and phenotyping of bacteria