Inhibitory effects of intact silkworm sericin on bacterial proliferation

Abstract

Sericins are derived from the outer layer of silk thread proteins of the common silkworm (Bombyx mori) and act as a glue to fix fibers of the developing cocoon. Although sericin has potential uses in various fields, including tissue engineering and the development of cosmetics, biological applications of intact sericin have yet to be identified. We previously developed transgenic silkworms that produce cocoons solely composed of sericin, from which we can readily prepare a solution of intact sericin. Here we report the effects of intact sericin on the proliferation of bacteria. The intact sericin does not kill bacteria, but colony size of Escherichia coli on culture media was reduced by up to 90% when cultured in the presence of intact sericin. In addition, treatment of intact sericin reduced colony size of Salmonella enterica, indicating a potential inhibitory effect of intact sericin on growth in Gram-negative bacteria. However, Gram-positive bacteria, including Staphylococcus aureus and Bacillus subtilis, were not affected by intact sericin. Thus, our results indicate that the cell wall structure of different bacteria may influence their sensitivity to the inhibitory effects of sericin.