NEW YORK (360Dx) – Scientists at the University of Jordan and Alfaisal University in Saudi Arabia have developed a rapid and low-cost diagnostic test for Staphylococcus aureus. The instrument-free, point-of-care test was shown to be effective in food samples as well as clinical samples, and the researchers now plan to develop it for detection of other pathogens and to start a spinoff company.
The assay is protease-based, lead researcher Mohammed Zourob said in an email, with the bacterial protease, if it is present, driving a chemical reaction. The test is essentially made up of a specific peptide sequence — one that is cleaved by the protease of S. aureus — attached to magnetic nanobeads, with a small strip of magnetic paper on the back.
"Upon protease exposure, the peptide sequence will be cleaved and the cleaved magnetic nanobeads will be collected on the magnetic paper attached to the paper support," Zourob explained.
In a study published last month in Biosensors and Bioelectronics the team demonstrated that the test could detect S. aureus with a one-minute incubation time.
The group showed it had a limit of detection as low as 7 colony-forming units per milliliter for pure broth culture of S. aureus. They also spiked the bacteria into various food samples and environmental samples collected in a hospital, and found LODs as low as 40 and 100 CFUs, respectively.
Importantly, the researchers also ran a series of clinical isolates, showing the test was specific for S. aureus, particularly methicillin-resistant S. aureus, or MRSA, and was able to differentiate the pathogen from similar organisms.
Tests to directly detect bacteria normally have poor sensitivity and are slow, Zourob said. "We are targeting the proteases from bacteria, not the bacteria itself, and that's why the assay is more sensitive and can be achieved in a shorter time," he added.
Zourob, an editor of a 2008 book on bacterial detection using biosensors, said the project was motivated by a desire to develop a better assay than the ones that are now available. The current bacterial detection techniques, he said, suffer from many major issues, such as poor sensitivity relative to the infectious doses, long analysis times, and requirements for washing reagents and additional wash steps.
The test developed by Zourob and his colleagues, on the other hand, also has technical expertise requirement advantages over PCR- and culture-based methods, in that it can be run easily by untrained personnel. It could potentially be run in a physician's office or at a patient's bedside, as opposed to in a clinical lab where current S. aureus testing is done.
US Food and Drug Administration cleared S. aureus and MRSA tests are available. But rapid assays, like those from from Alere, are usually run with blood culture or microbiology culture samples, while PCR-based tests from firms like Cepheid, Becton Dickinson, and Roche, are typically run by trained personnel in a lab.
There have been similar biosensor-based methods described in the literature, according to the study. One, also published in Biosensors and Bioelectronics, used magnetic nanoparticles to develop a colorimetric test that specifically bound S. aureus bacterial cells. That test, however, required 40 minutes of run time and had limits of detection of 1.5×103 and 1.5×105 CFU. Another device, described in Sensors and Actuators, was also colorimetric but relied on vesicles in celluloid so might be more complicated to manufacture. A third method using antibody-labeled gold nanoparticles has an advantage of an easy visual readout, but in some cases samples require purification and concentration to yield a specific and sensitive response.
There have also been a few protease-based biosensors described recently, for example to detect larval stages of Schistosoma mansoni parasites, or non-specific tests for wound infections or inflammatory biomarkers of periodontitis.
Meanwhile, the protease-based method being developed by Zourob and colleagues can also be used to specifically detect other pathogens as well. "We have already demonstrated in our lab that this technology can detect 13 other bacteria and a few viruses and toxins," he said.
The group now has three patents on the assay, Zourob said, and is establishing a spinoff company now to commercialize the technology. Specifically, he noted that the group is in the process of securing funding from venture capital and investors.