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Journal of Biochemistry Advance Access published online on August 4, 2006
Journal of Biochemistry, doi:10.1093/jb/mvj171
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© 2006 The Japanese Biochemical Society.
Received April 17, 2006
Accepted July 24, 2006

Regular Paper

Use of Silkworm Larvae to Study Pathogenic Bacterial Toxins

Muktadir S. Hossain 1, Hiroshi Hamamoto 2, Yasuhiko Matsumoto 2, Iony M. Razanajatovo 2, Jorge Larranaga 2, Chikara Kaito 2, Hiroshi Kasuga 2, and Kazuhisa Sekimizu 2 *

1 Laboratory of Microbiology, Graduate School of Pharmaceutical Sciences, The University of Tokyo, 3-1, 7-Chome, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan; Present address: Laboratory of Biochemistry, National Cancer Institute, National Institutes of Health, Bethesda, MD20892, USA
2 Laboratory of Microbiology, Graduate School of Pharmaceutical Sciences, The University of Tokyo, 3-1, 7-Chome, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

* To whom correspondence should be addressed.
Kazuhisa Sekimizu, E-mail: sekimizu{at}mol.f.u-tokyo.ac.jp


  Abstract

Injection of stationary phase culture-supernatants of Staphylococcus aureus and Pseudomonas aeruginosa into the hemolymph of silkworm larvae caused their death, whereas a culture-supernatant of a non-pathogenic strain of Escherichia coli did not. A culture-supernatant of a mutant of agr, a global virulence regulator of S. aureus that is required for exotoxin production, was much less toxic to silkworm larvae. A culture-supernatant of a disruption mutant of the S. aureus beta-toxin gene did not kill larvae, whereas one of a deletion mutant of alpha-toxin, gamma-toxin, or aureolysin killed larvae, indicating that the beta-toxin gene is required for staphylococcal supernatant-mediated killing of silkworm larvae. The 50% lethal doses (LD50) of staphylococcal alpha-toxin and beta-toxin, Pseudomonas exotoxin A and diphtheria toxin were 12 µg/g, 9 µg/g, 0.14 µg/g and 1.1 µg/g, respectively. As the purified toxins killed the larvae, silkworm larvae could be used as a model to study the actions of pathogenic bacterial toxins in animal bodies.

Keywords: animal model; infection; pathogenic bacterial toxins; silkworm larva; Staphylococcus aureus.
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