A
new, easy-to-adapt and inexpensive analytical procedure has been developed by
researchers from the Institute of Physical Chemistry of the Polish Academy of
Sciences in Warsaw. The main role is played by innovative bioconjugates --
luminescent, magnetic microparticles coated with appropriately selected
bacteriophages.
The
detection device in the new technique for identifying bacteria is a flow
cytometer. Despite the seemingly formidable name it is quite a simple and
relatively inexpensive piece of equipment, available in many hospitals, where
it is used commonly in blood tests. In the cytometer the sample is passed
through a nozzle from which the stream that flows is so narrow that all the
larger particles in the solution, particularly cells, have to flow one by one.
The stream is lit by lasers and surrounded by detectors that record the light
reflected from individual particles, scattered to the sides and emitted by
them.
The
main problem was to develop a method for labelling the bacteria to be easy to
intercept them in the test sample and identify them with great certainty with
the aid of the cytometer. To do this, researchers decided to construct special
bioconjugates, i.e. complexes formed by the combination of microparticles with
biomolecules. The biological element was a bacteriophage, which is a virus
infecting a particular species of bacteria (the IPC PAS experimenters used the
T4 bacteriophage, attacking Escherichia coli bacteria). The bacteriophages were
coupled with microparticles capable of emitting light that could be easily
registered on the cytometer and exhibiting magnetic properties. The latter was
essential, because it made it possible to separate the bioconjugates from other
particles in the sample with a simple magnet.
With
the method, the sample -- it can be a physiological fluid obtained from the patient,
or a food product, e.g. carrot juice -- is diluted and then a small amount of
previously prepared bioconjugates is added to the solution. After this, it
takes a short while for the bioconjugates to attach to the bacteria. Next, a
magnet is applied to the test-tube with the liquid and all bioconjugates are
attracted, including those with the attached bacteria. After pouring out the
remainder of the sample and re-dilution of the separated precipitate, the
solution is passed through the cytometer.
For
further details see:
Posted by Dr. Tim Sandle