Researchers from the Georgia Institute of Technology and the
Centers for Disease Control and Prevention (CDC) have developed a new
laboratory test that can rapidly identify the bacterium responsible for staph
infections.
This new test takes advantage of unique isotopic labeling
combined with specific bacteriophage amplification to rapidly identify
Staphylococcus aureus.
Quickly and accurately detecting infections caused by S.
aureus is critical because the pathogenic bacterium causes a broad spectrum of
infections, ranging from acute to chronic disease, which need to be treated in
a prompt manner with the correct antibiotic.
The test uses mass spectrometry to quantify the number of S.
aureus organisms in a large number of samples in just a few hours, compared to
a day or two for culturing techniques typically used to detect this bacterium.
“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,” said Facundo Fernández, an associate professor
in the Georgia Tech School of Chemistry and Biochemistry.
Details of the new staph infection detection method were
published in the January issue of the journal Molecular and Cellular
Proteomics. Partial funding for this research was provided by 3M and the CDC/Georgia
Tech seed award program.
Fernández together with Carrie Pierce, Jon Rees and John
Barr from the CDCs Division of Laboratory Sciences created this test.
“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,” explained Pierce, a research chemist at the CDC who
also worked on the project as a graduate student at Georgia Tech.
To run their test, the researchers first inject a known
amount of bacteriophage labeled with nitrogen-15 into a sample. The phages —
which are viruses that infect bacteria — infect only live S. aureus cells,
which then multiply and amplify the phage signal. Following a two-hour
incubation, the researchers break up proteins from the phage shell into
component peptides using a trypsin digest technique.
Then they analyze the sample 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.
“The strength of this technique is coupling a well-characterized
method for identifying bacteria with a modern detection device, such as a mass
spectrometer,” said Barr, biological mass spectrometry lead in the CDCs
Division of Laboratory Sciences. “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.”
This prototype mass spectrometry-based technique has been
optimized to detect low concentrations of bacteria that should allow clinicians
to diagnose staph infections without the need for a significant culture period.
Coupled with standard laboratory robotics, the test will
reduce manual labor and subjective interpretation of results inherent in
traditional techniques.
“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,” said Rees. “This additional piece of information may be the
key to wide acceptance of the method.”
Posted by Sean Fenske, Editor-in-Chief, MDT
