The performance of a new diagnostic test platform that rapidly identifies Staphylococcus aureus (S. aureus, “staph”) bacteremia and determines antibiotic resistance or susceptibility in as little as five hours was presented at the 109th General Meeting of the American Society of Microbiology in Philadelphia.
The poster summarized the performance of the test prototype in a multisite clinical trial in late 2008 in three separate clinical microbiology laboratories. In 711 evaluable clinical samples, the test demonstrated perfect specificity for S. aureus, with no cross reactivity against non-target organisms, and high sensitivity, detecting nine out of every 10 S. aureus present. Specificity in determining methicillin-resistant S. aureus (MRSA) was also found to be high, at 99%, while methicillin-sensitive S. aureus (MSSA) specificity exceeded 99%.
“Current methods rapidly identify Staphylococcus to the species level but are not capable of determining resistance,” said lead author Julie D. Kingery, M.D., of Johns Hopkins University School of Medicine. “Complex molecular assays can do this, however they are frequently expensive, require special expertise, and their utility as rapid tests is reduced because they may need to be batched. This assay allows tests to be set up in real-time and is easy-to-use. Because no instrumentation is required, the assay is also inexpensive.”
MicroPhage’s prototype assay is designed to rapidly identify Staphylococcus aureus (staph) bacteria and determine methicillin resistance (MRSA) or susceptibility (MSSA) in suspected cases of bacteremia – bacteria in the blood. The research preceded FDA required clinical studies, which are scheduled to begin this summer. Clinical testing sites included Johns Hopkins University Hospital, Northshore University Healthcare (IL), and the University of Maryland Medical School.
The MicroPhage test platform requires no instrumentation and is composed of two small reaction tubes for incubating blood culture specimens. After five hours, the incubated samples are added to a dual dipstick-like detector, which looks much like a pair of home pregnancy tests. One part of the detector shows if the sample is infected with S. aureus bacteria and the other shows if it is susceptible or resistant to the antibiotic.
According to Drew Smith, Ph.D., Director, Research and Development at MicroPhage, test performance at the three sites exceeded all study goals for the prototype. “This test performed more like a market-ready test, producing excellent results with regard to specificity,” said Smith. “We are confident the final manufactured product will be robust and meet the demands of the clinical laboratory market and the scrutiny of the FDA, including increased test sensitivity. We have already made significant improvements to this test since the trial.”