A new form of botulinum neurotoxin, or BoNT, was recently discovered by scientists examining a case of infant botulism. Source: Wikipedia.
Botulism is a rare but extremely dangerous disease caused by Clostridium botulinum bacteria. Once inside a person’s body, these bacteria produce substances known as botulinum neurotoxins, or BoNTs. BoNTs are the most toxic substances known to man; exposure to even a tiny amount of these chemicals is often lethal. Recently, researchers Jason Barash and Stephen Arnon discovered a new form of the deadly toxin, designated BoNT/H, after inspecting a case of infant botulism (1).
Each C. botulimum bacterium produces one or two specific BoNTs. Before Arnon’s and Barash’s research, seven types of BoNT were known (named BoNT/A through BoNT/G), four of which cause most of human botulism cases (1, 3).
C. botulimum bacteria are classified by the types of BoNTs they produce. To make this classification, scientists use a procedure known as a mouse bioassay. First, a colony of the bacteria is cultured from a fecal sample from the infected patient. Small numbers of these bacteria are then injected into a group of mice (1).
Some mice in this group also receive doses of antitoxins capable of recognizing and neutralizing particular BoNTs. Mice who receive the correct antitoxins will not suffer symptoms of the infection, thus revealing the BoNTs produced by the bacteria (1).
In one case of infant botulism, Barash and Arnon isolated the bacteria from the patient and performed the standard mouse bioassay. Antitoxin B, the antitoxin to BoNT/B, was most effective, protecting mice for the first 24 hours of their infection. However, even the mice that received antitoxin B still suffered the characteristic symptoms of botulism (1).
Because C. botulinum bacteria can produce more than one BoNT, Barash and Arnon gave mice combinations of two antitoxins. Again, mice that received antitoxin B were somewhat protected. Combinations of antitoxin B with either antitoxin A or F were about twice as effective as was antitoxin B alone. Yet, all of the mice continued to exhibit symptoms of botulism (1).
In a final attempt, Barash and Arnon injected the mice with a heptavalent antitoxin. The heptavalent antitoxin could recognize and neutralize all seven of the known BoNTs, but the mice that received this antitoxin still eventually suffered symptoms of botulism. Because no known antitoxin could fully protect the mice, the infecting bacteria must produce a previously unknown form of BoNT (1).
Continuing the alphabetical system of classifying BoNTs, this new toxin was named BoNT/H. Because antitoxin A and F provided some protection against BoNT/H, the new toxin is structurally similar to BoNT/A and BoNT/F. Moreover, because antitoxin B provided the mice some protection, Barash and Arnon concluded that the bacteria produced both BoNT/B and BoNT/H, the first known C. botulinum bacteria to do so (1).
The discovery of a new form of BoNT is quite significant. To protect people from further dangerous infections, antitoxins to BoNT/H will have to be identified and produced. Botulism is a rare but deadly disease, and scientists will have to take the proper precautions to prepare the public against this development.
References
1. J. R. Barash, S. S. Arnon, A Novel Strain of Clostridium botulinium That Produces Type B and Type H Botulinium Toxins. Journal of Infectious Diseases (2013), doi: 10.1093/infdis/jit449.
2. Botulism, Centers for Disease Control and Prevention (2011). http://www.cdc.gov/nczved/divisions/dfbmd/diseases/botulism/#what (October 19, 2013).
3. Botulinium Toxin, Medscape (2012). http://emedicine.medscape.com/article/325451-overview (October 19, 2013).
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