Secretion Systems are protein complexes found in the cell membranes of bacteria. Secretion systems are used to secrete proteins that assist bacteria in the invasion of host cells. There are two types of secretory systems: 1) proteins from the cytoplasm of bacteria are transported directly through into the cell membrane of the host and 2) proteins are transported out of the inner cell membrane of the bacteria into the periplasm before exiting the outer cell membrane into the host cell.