When you are dealing with a deadly poison that can be found in food and is a potential terrorist weapon, you want the best detection tools you can get. Now, researchers in France have demonstrated an improved method to detect the most deadly variant of the botulinum neurotoxin, which causes botulism. Their test provides results faster than the standard method and accurately detects even low concentrations of the toxin.
Botulinum neurotoxin—one of the deadliest poisons known to humans—is produced by the bacterium Clostridium botulinum. This toxin can be found in improperly canned foods and is considered a potential terrorist weapon due to its ability to kill at very low concentrations if added to food, water, or the air supply. Individuals who become sick from the toxin develop progressive paralysis that is fatal 60% of the time if left untreated. But if a patient receives treatment in time, the likelihood of death falls to less than 5%.
Unfortunately, the current standard blood test for detecting the botulinum toxin in adults is slow—and gruesome. Blood from the patient is injected into mice; if the rodents develop symptoms of botulism and die, the test is positive. But it can take as long as four days to get results from the mouse test, which limits its usefulness in situations where treatment decisions need to be made quickly. What’s more, the patients who have the least amount of time to spare often don’t test positive at all. The botulinum toxin moves out of the blood and into muscle as the disease progresses. As the concentration of the toxin in the blood falls, the mice become less likely to react to it in time—even as the patient becomes sicker and sicker.
Molecular neurobiologist Christian Lévêque of the French biomedical research agency INSERM in Marseille and Aix-Marseille University in Provence thought it was high time for a change. So he and his team set out to design a new test that took advantage of the molecular processes behind the botulinum neurotoxin’s paralyzing effect. They focused on botulinum neurotoxin A, which causes most of the botulism cases in the United States. (Botulinum neurotoxins B, E, and F can also cause disease.)
Botulinum neurotoxin A causes paralysis by breaking apart a protein called SNAP-25, which helps nerves and muscles communicate. Lévêque and his team affixed SNAP-25 to a tiny chip and exposed it to blood containing the A toxin. Then, the researchers introduced an engineered antibody that reacts with SNAP-25 only after it has been dismantled in the manner particular to the A neurotoxin. If the antibody reacted with the chip, they knew the blood sample contained A toxin. Using this method, Lévêque and his team could detect the toxin in a matter of hours, instead of days, and at much lower concentrations than the mouse test, they report in an upcoming issue of Biosensors and Bioelectronics.
Attaching SNAP-25 to the chip proved to be a key advantage of the new method, Lévêque says. This trick allows the test to react directly to a patient’s blood, which means very little precious time is wasted preparing the sample for analysis. “Sample preparation often represents a bottleneck” in clinical tests, Lévêque explains. His team’s test, on the other hand, “is very simple, as samples just need to be diluted and introduced into the apparatus.”
The new test "is very fast and sensitive," says Luis Polo-Parada, a medical nanotechnologist at University of Missouri, Columbia, who was not involved with the research. However, he cautions that additional labs will need to confirm the test’s effectiveness before it will be ready for use in patients. Both Polo-Parada and disease detection researcher Markus Kalkum of the Beckman Research Institute of City of Hope in Duarte, California, who was not involved with the research, hope the test will be expanded to cover the B, E, and F neurotoxins, too. Lévêque says his group is already working on that.