Not all spider silks are antimicrobial

Spider silks are thought to have antimicrobial properties that prevent rapid degradation. Despite its biomedical potential, little research has focused on antimicrobial properties of spider silks. We tested the antimicrobial properties of gluey gumfoot capture threads of the western black widow spider, Latrodectus hesperus Chamberlin & Ivie, 1935, both for whole threads and after separating viscid silk from water soluble glue components using a water wash. Capture threads, unlike dry dragline silk, have a glue coating that may promote different interactions of bacteria with the material. Antimicrobial activity was assessed in an aqueous Escherichia coli cell culture and growth of colonies was counted over 24 hours. In contrast with previous research, mostly on dry dragline silk, we found an increase in bacterial growth for whole gumfoot thread treatment, but no effect of the solid and water-soluble components individually. These results suggest that better and proper procedures are needed for testing antimicrobials in silks, with controlled experiments using just one type of silk.