New test developed for identifying S. aureus

Pierce CL. Mol Cell Proteomics. 2012;doi:10.1074/mcp.M111.012849.

Researchers from the Georgia Institute of Technology and the CDC have developed a new laboratory test that can rapidly identify Staphylococcus aureus, according to results of a study.

The test uses unique isotopic labeling combined with specific bacteriophage amplification to rapidly identify S. aureus, according to a press release from GIT. The test uses mass spectrometry to quantify the number of S. aureus organisms in a large number of samples in just a few hours vs. 1 to 2 days for culturing techniques.

“Our method for detecting staph infections using mass spectrometry will be valuable in a variety of situations, but will be crucial when a large number of people need to be tested very quickly, which will ultimately improve treatment,” Facundo Fernández, PhD, an associate professor in the GIT School of Chemistry and Biochemistry, said in a press release.

To run the test, the researchers first inject a known amount of bacteriophage labeled with nitrogen-15 into a sample. The phages infect only live S. aureus cells, which then multiply and amplify the phage signal. After a 2-hour incubation, the researchers break up proteins from the phage shell into component peptides using a trypsin digest technique. The sample is then analyzed using liquid chromatography with tandem mass spectrometric detection. By detecting peptides from the protein shell of the phage, the researchers can measure the concentration of S. aureus in the sample, according to the findings published in Molecular & Cellular Proteomics.

Disclosure: Partial funding for this research was provided by 3M and the CDC/Georgia Tech seed award program.

C. Buddy Creech, MD, MPH

We stand at the precipice of tremendous growth in the availability of rapid diagnostics for infectious diseases. We are already familiar with the use of polymerase chain reaction (PCR) for the rapid detection of respiratory viruses, tuberculosis and other pathogens, but each test has imperfections. For S. aureus, these include a changing target for PCR amplification (eg, European strains of MRSA with a modified mecA gene) or the requirement for culture prior to use of these specific molecular techniques.

The technology used in this study theoretically allows for the rapid detection (1) of living staphylococci (2), even with a very low burden of disease (3). Tackling this trio of characteristics is exciting as we consider potential applications in which we desire to prove sterility (recognizing that PCR cannot differentiate live from dead organisms) or very quickly assess a sterile site for even small numbers of organisms (eg, cerebrospinal fluid, joint fluid). While the availability of mass spectrometers is not yet universal in clinical laboratories, the use of labeled bacteriophages is certainly retro-science. Once the workhorse of molecular typing methods, bacteriophage-based diagnostics is a creative, and likely to be effective, strategy for diagnostics.

Maybe more important, however, is that in an age where the balance between antimicrobial stewardship and resistance is tenuous at best, more attention is being directed toward rapid diagnostics. Together with better assays for fastidious organisms, we may see more and more such technologies in the clinical arena.

– C. Buddy Creech, MD, MPH

Assistant professor, pediatric infectious diseases Associate director,

Vanderbilt Vaccine Research Program Vanderbilt University School of Medicine

and the Monroe Carell, Jr. Children’s Hospital at Vanderbilt

Disclosure: Dr. Creech reports no relevant financial disclosures.

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