New test grabs Streptococcus pyogenes by the throat
Scientists have developed a non-invasive mass spectrometry-based diagnostic technique that can diagnose strep throat in less than 10 seconds.
Almost all of us will experience a sore throat at some point in our lives, and a number of these sore throats (~30%) will be caused by infections with Streptococci bacteria. Streptococcal pharyngitis, which is usually caused by Streptococcus pyogenes, is commonly known as ‘strep throat’ and can be treated with antibiotics if successfully diagnosed. Although the vast majority of strep throat cases resolve themselves within a few days, Streptococcal infections can lead to serious complications, such an inflammatory disease called rheumatic fever that can result in heart failure and even death. Children and the elderly are particularly susceptible to complications, so for these individuals, the rapid diagnosis and treatment of strep throat can be life-saving.
At the moment, strep throat is diagnosed through a rapid antigen detection test (RADT), which provides results within 15–20 minutes. However the false positive rates for such tests are high and training is essential for reliable results. As such, simpler and even more rapid tests are needed.
Inspired by his own experiences of strep throat as a child, Alan Jarmusch, along with colleagues at Purdue University, US and the University of Turin, Italy, has developed a simple test that can spot Streptococcus pyogenes within seconds. The system is based on touch spray ionisation-mass spectrometry. A swab is taken of the patient’s throat before a voltage generates ions from the sample, some of which will be derived from molecules unique to the bacteria. The sample is then run through a mass spectrometer and pattern recognition software is used to identify whether peaks representative of Streptococcus pyogenes specific molecules are present in the resulting spectrum.
Touch spray ionisation-mass spectrometry has been used in a diagnostic setting before, but the sampling probes have typically been metallic and sharp, and not at all suitable for sampling the soft tissues in someone’s throat. As such, the real challenge was to develop a mass spectrometry-friendly swab that could be used to sample the patient’s throat in a non-invasive manner, whilst also being compatible with standard mass spectrometry equipment. The team has achieved this, and in doing so have developed a system with the potential to non-invasively diagnose a wide range of different diseases, that may have even wider-reaching applications in drug testing and forensics.
‘It is a striking application of ambient ionisation mass spectrometry,’ says Richard Zare, a chemical analysis expert at Stanford University, US. ‘As mass spectrometers become miniaturised and more affordable, we can look forward to many more uses of ambient ionisation mass spectrometry as a medical tool to diagnose disease states.’
Jarmusch and co-workers now plan to extend the methodology to incorporate additional bacteria.
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