Re: Could Anthrax Bacteria grow inside of a common Cockroach?

Hi Gus,

The answer to your question depends a bit on how the anthrax bacteria get into the cockroach. If the cockroach simply eats some food covered in anthrax, its very probable that the bacteria will survive inside the cockroach and that the roach will not die. I can’t say for sure… no one has actually fed anthrax to cockroaches to see what happens… but we can make a good guess at what will happen by looking at close relatives of the anthrax bacteria and what happens when roaches eat them.

One close relative of the anthrax bacteria (whose scientific name is Bacillus anthracis) is the bacteria Bacillus cereus, a type of bacteria that gives us food poisoning [1, 2]. It turns out that Bacillus cereus survives and grows quite well in the hindguts of cockroaches without causing them any problems at all [3]. While that doesn’t say for sure that anthrax would also survive in the guts of cockroaches, it’s a very good bet that the anthrax bacteria would be just fine if it was eaten by cockroaches.

Would the cockroach get anthrax from eating the bacteria? Probably not - the poison that anthrax bacteria produce is not a simple substance like cyanide or arsenic that can kill just any cell. The anthrax toxin is actually pretty large and complex and can only harm certain types of cells [4], and these cell types are not found in the stomach and intestines of insects.

Things are a bit different if you injected anthrax into cockroaches – the bacteria would try to grow inside the nutrient rich blood of the cockroach, while the cockroach would try to get rid of the bacteria by ‘eating’ them with special blood cells or by making special poisons of its own that would kill the anthrax bacteria and not harm the roach. Whether the roach lived or died would depend on whether you injected more bacteria into the cockroach than its immune system could handle [5]. This would not be the same as giving the cockroach anthrax, however… its not very likely that the poison the anthrax bacteria makes can harm cockroaches. Instead, it would be like the human disease called blood poisoning or septicemia [6] where bacteria that are normally harmless (including some which are normally helpful when found on the skin or in your intestine) can become deadly if they get into your blood.

I hope this answers your question,

Doc Clarke.

References

[1] Center for Disease Control fact sheet on Bacillus cereus: http://vm.cfsan.fda.gov/~mow/chap12.html

[2] Ivanova, et al. 2003. Genome sequence of Bacillus cereus and comparative analysis with Bacillus anthracis. Nature 423: 87 – 91.

[3] Feinberg, L. et al. 1999. Arthromitus (Bacillus cereus) symbionts in the cockroach Blaberus giganteus: dietary influences on bacterial development and population density. Symbiosis 27: 109 – 123.

[4] Protein Data Bank article on the anthrax toxin: http://www.rcsb.org/pdb/molecules/pdb28_1.html

[5] The subject of insect immunity is a very complex one… they use some defenses that we have (blood cells that eat bacteria) but lack others (for example, insects don’t make antibodies). Most of the articles on the topic get very complex very quickly, but if you are interested, I would recommend tracking down an article by Gillespie, Kanost, and Trenczek called Biological Mediators of Insect Immunity published in the 1997 edition of Annual Review of Entomology (vol 42, pages 611 to 643). It’s a bit dated, but is probably the best starting point for anyone interested in insect immunity.

[6]Medline article on septicemia: http://www.nlm.nih.gov/medlineplus/ency/article/001355.htm