That mechanism is a miniscule protein tip of a needle - like structure docked on the bacterial surface. (news.wsu.edu)
As the tips of my needles loop through the strand of yarn, I wonder about the first person who realized that this series of knots could be made by needles and would hold together. (ktmade.com)
By generating high electric fields at the tip of the needle, Hughes can inject electrons into the molten polymer to create negatively charged ions. (newscientist.com)