CDC research chemist Carrie Pierce (left) and Georgia Tech School of Chemistry and Biochemistry associate professor Facundo Fernández examine a sample before they subject it to a new laboratory test they developed that can rapidly identify the bacterium responsible for staph infections. Photo: Gary Meek |
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 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 CDC’s 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 CDC’s 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.”
