Serum lysis refers to the lysis of gram-negative bacteria by the complement protein complex known as the Membrane Attack Complex or MAC. The pores introduced into the outer membrane and possibly the cytoplasmic membrane of gram-negative bacteria my MAC results in their lysis. The LPS of the cell wall is the principle target for complement in gram-negative bacteria by activating the alternative complement pathway (def) and serving as a binding site for C3b as well as the site for formation of MAC.