Transmission

Hello,
How I can block Transmission in my organization using iptables? I have rules
iptables -I FORWARD -m string --string "BitTorrent protocol" --algo bm --to 65535 -j DROP
iptables -I FORWARD -m string --string "info_hash" --algo bm --to 65535 -j DROP
This works well for uTorrent but does not ...