New lab method quickens anthrax detection
proteins within an infected blood sample at extremely low levels
has been developed by researchers, who believe the system will
become useful in developing reliable ways to diagnose anthrax
infections.
Current detection methods rely on injecting live animals or cell cultures with samples for analysis and require up to several days before results are available - a huge disadvantage for a disease that requires swift and decisive action to contain its spread.
This new lab technique is said to produce unambiguous results in approximately one hour and the researchers hope the system will, in addition, screen large numbers of drugs as possible therapies for blocking the bacteria's toxic effects.
The method, developed by researchers at the National Institute of Standards and Technology (NIST), the US Army Medical Research Institute of Infectious Diseases and the National Cancer Institute, works by detecting changes in current flow when anthrax proteins are present in a solution.
An anthrax protein called "protective antigen" spontaneously forms nanometer-scale pores that penetrate the surface of an organic membrane.
When a voltage is applied across the membrane, positively and negatively charged ions flow freely in both directions through the pore. When additional anthrax proteins called lethal factor (LF) or edema factor (EF) are present, however, the proteins bind to the outside of the pore and shut down the flow of ions in one direction.
This change in current flow depends on the concentration of the proteins in the solution and can detect amounts as low as 10 picomolar (trillionths of a mole).
"We hope this system will lead to a method for rapidly screening agents that inhibit the binding of LF or EF to these pores," said NIST's lead investigator John Kasianowicz.
Live anthrax antibodies seem to do exactly that. When antibodies were present in the test solution and then LF was added, the current flow remained unchanged, indicating that the anthrax proteins were unable to bind properly.
Indeed, the researchers said that their long-term goal would be to find drugs with few side effects that also interfere with this binding process.
While current methods, which include growing cultures, PCR analysis, antibody tests, microscopy, fluorescence assay and DNA fingerprinting provide accurate means for detection and identification of the toxin, quicker and more cost effective methods will always be welcomed.
For the past one and half years, the United States Post Office hasbeen using a microfluidic cartridge-based biothreat agent detection system,called the GeneXpert, that utilises realtime PCR.
The system is completely hands-off, obtaining a result in 35-37 minutes. Its claim of 10 picomole sensitivity for the newly described membrane voltage method means the test can detect 100 billion molecules comparing favourably to the 10-100 organism sensitivity of the realtime PCR method.
