Tigers and gold: SSPUís Office of Extramural Research funds new technologies for infectious disease pathogen detection *
By Brian W.J. Mahy, MA, PhD, ScD, DSc (Hon)
What is CCID doing with a tiger and gold chips? Those exotic images have provided a short-hand way of describing two research projects being funded by the coordinating center’s Office of Extramural Research, now in NCID and soon to become part of the Extramural Research Program Office (ERPO, proposed) in the Strategic Science and Program Unit (SSPU, proposed).
The two groups ERPO arranged funding for are engaged in state-of-the-art research to develop new approaches to detect bacteria and viruses that cause infectious diseases. The funding for these research grants came from the Coordinating Office for Terrorism Preparedness and Emergency Response (COTPER). The principal investigators of both groups recently gave seminars on their work in the Tom Harkin Global Communications Center.
Dr. David Ecker and his team at the Ibis division of Isis Pharmaceuticals, Carlsbad, Calif., are using electrospray ionization mass spectrometry** to study the nucleotide composition of genes that have been amplified by the PCR (polymerase chain reaction) process so that scientists can identify the type and number of disease-causing bacteria in a patient’s respiratory secretions.
For example, Francisella tularensis, Yersinia pestis, Escherichia coli 0157, and Pseudomonas aeruginosa could all be detected and distinguished. The method can also detect viruses and can distinguish SARS coronavirus from other human coronaviruses such as 229E and OC43; it could also be used to distinguish subtypes and strains of influenza.
Dr. Ecker has termed this biosensor method TIGER (Triangulation Identification for the Genetic Evaluation of Risks). At the heart of this method is the design and use of PCR primers (short pieces of single-stranded DNA), which bind to the relatively unchanging regions of the DNA template and are designed to flank the more changeable regions, which then are amplified by repeated copying. The concept could also be applied to the detection of fungi and protozoa. The difference between the traditional PCR method and the TIGER method can be illustrated this way: Traditional PCR answers the question, “Is infectious organism X in my sample?” But, the TIGER method answers the question, “Which infectious organisms are in my sample?”
Several CCID scientists are already collaborating with Ecker and his team, including Bernard Beall, Brandi Lombard, Kevin Tong, and Bob Wohlheuter. The equipment for the TIGER biosensor technology is being installed and tested within CCID under the care of the Biotechnology Core Facility the week of September 25. Jose Guitierrez of Ibis Biosciences will conduct training of CDC users from October 16—18.
Gold nanoparticle photonic sensors
Dr. Ashutosh Chilkoti and his team at Duke University are using nanoparticles, 10-100 nm diameter, prepared from noble metals, particularly gold, which have unique size, shape, and optical properties. The colors of the particles are caused by the interaction of light with surface electrons. In ancient times, the Romans used gold colloids to color glass:
As a further refinement, Dr. Chilkoti’s group developed a “chip” made by adding a transparent gold colloid layer on a glass surface. The group then showed that the glass chips displayed colloidal surface plasmon resonance*** which could be detected in a regular spectrophotometer. The chips can be used by attaching biotin or streptavidin to the surface. (Streptavidin is a small bacterial protein that binds to the vitamin biotin; the streptavidin-biotin combination can be used to link molecules such as radioisotopes and antibodies.) Chilkoti is using this method to develop a way to detect anthrax protective antigen.
*For a more technically detailed version of this article, click here.
**What is a mass spectrometer?
A mass spectrometer is an instrument that measures the masses of individual molecules that have been converted into ions, i.e., molecules that have been electrically charged. An actual mass spectrometer ranges in size from about the size of a home microwave oven to large research instruments that dominate entire rooms. For a more detailed explanation of mass spectrometers, click here.
***What is surface plasmon resonance?
Surface plasmon resonance occurs when light is reflected off thin metal films. A fraction of the light energy occurring at a sharply defined angle can interact with the free electrons in the metal film, or plasmon, thus reducing the intensity of the reflected light. For a more detailed description of this process, click here
Ecker, DJ et al (2005) Rapid identification and strain-typing of respiratory pathogens for epidemic surveillance. Proc Natl Acad Sci USA 102, 8012-8017.
Nath N, and Chilkoti A (2002) A colorimetric gold nanoparticle sensor to interrogate biomolecular interactions in real time on a surface. Anal Chem 74 504-509.
About the author: Dr. Brian Mahy is acting director of the Office of Extramural Research in the CCID Strategic Science and Program Unit (SSPU, proposed).