Researchers have designed a new laboratory test that can quickly identify the bacterium that causes Staphylococcus aureus infections. The findings have been published in the January issue of the journal Molecular and Cellular Proteomics.
The researchers, from the Georgia Institute of Technology and the Centers for Disease Control and Prevention (CDC) have based their test on unique isotopic labeling combined with specific bacteriophage amplification to rapidly identify Staphylococcus aureus by using mass spectrometry to quantify the number of S. aureus organisms in large numbers of samples within few hours, as compared with the standard culturing techniques that require one or two days to identify the bacterium.
A rapid and precise detection of S. aureusinfections is vital as it can cause a broad spectrum of infections, which can range from acute to chronic disease that require rapid treatment with the appropriate antibiotic.
Facundo Fernández, an associate professor in the Georgia Tech School of Chemistry and Biochemistry declares:
“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.”
Pierce, a research chemist at the CDC who was involved in the project as a graduate student at Georgia Tech explained:
“The simplicity of sample preparation, the low cost of required reagents and the increased availability of mass spectrometers in clinical laboratories make this new method a cost-effective way to rapidly and effectively detect staph infections, which must be treated quickly to prevent spread of the disease.”
The test involves injecting a known amount of bacteriophage labeled with nitrogen-15 into a sample. The phages, viruses that infect bacteria, only infect live S. aureus cells, which subsequently multiply and amplify the phage signal. After two-hours of 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. The researchers can measure the sample’s S. aureus concentration by detecting peptides from the protein shell of the phage.
Barr, biological mass spectrometry head in the CDC’s Division of Laboratory Sciences commented:
“The strength of this technique is coupling a well-characterized method for identifying bacteria with a modern detection device, such as a mass spectrometer. By labeling input phage with heavy nitrogen isotopes, we were able to use mass spectrometry to effectively distinguish between the parent and progeny phage, thus enhancing the selectivity of the method.”
The researchers have optimized the prototype of this mass spectrometry-based technique to identify low concentrations of bacteria, which should enable clinicians to diagnose staph infections without needing significant culture periods. The test will reduce manual labor and subjective interpretation of results that occur in traditional techniques when combined with standard laboratory robotics.
Rees concludes:
“An exciting aspect of this phage method is that with small modifications to the procedures, resistance and susceptibility to a number of different antibiotics can be determined in addition to bacterial identification. This additional piece of information may be the key to wide acceptance of the method.”
Written by Petra Rattue