Experiment 2: antimicrobial effect of silk in vitro
Six 90 mm Petri dishes of media (65 g Sabouraud dextrose
agar, 1 ml 10% streptomycin sulphate and 1 ml 5% chloramphenicol
per litre of water) were each divided into six
equal sections. Silk extracts were made by placing three
0.5 cm2 pieces of silk in 1.5 ml pentane (99?%, Sigma) for
3 h. On each agar dish, a 0.5 mm2 piece of silk was placed
in two sections, 100 ll of silk extract was placed in two
other sections and 100 ll of pentane placed in the final two
sections. The media dishes were left for 30 min for any
antimicrobial compounds to absorb into the media, and 1 ml
of a 1 9 107 conidia/ml suspension of Metarhizium anisopliae
was then spread evenly over the plate. The media
dishes were stored at 27C and 80% RH for 4 days, after
which the presence or absence of Metarhizium growth in
each section was assessed.