Adhesins are responsible for recognizing and binding to specific receptor mieties of host cells, thus triggering signal transduction cascades in the host and invader.

1. In many cases adhesins are assembled into hair-like appendages called pili or fimbriae that extend out from the bacterial surface.
2. In other cases, the adhesins are directly associated with the microbial surface (so called nonpili or afimbrial adhesins).