Pili are short, hair-like appendages that protrude through the capsule and serve in the attachment of bacteria to surfaces. The ability of the pili to attach to host cell receptors determines the type of tissues that a bacterium can colonize. A specialized pilus known as the sex pilus is involved in the transfer of DNA from one bacterium to another via a process known as conjugation. This ability to transfer DNA is an important factor in the spread of antibiotic resistance genes through a microbial community.

Another difference between bacteria and viruses is motility. Viruses do not possess structures that enable them to move purposefully through the environment. Bacteria, on the other hand, are able to move through the environment using a structure known as the flagellum.