The Gram negative bacterial outer membrane protects the bacterium from external toxins such as antibiotics. This is partially responsible for Gram negative bacteria becoming the fastest emerging source of antibiotic resistance. We are developing models of these bacterial outer membranes and have successfully recreated the characteristic lipid asymmetry (with lipopolysaccharide (LPS) on the outer leaflet and phospholipids on the inner). In order to fully recreate the membranes we will need to incorporate more complex LPS versions to mimic pathogenic bacteria. Pathogenic bacteria contain a proportion of longer LPS molecules which are related to their virulence. Recently we have incorporated LPS containing one or two O antigens into the model and now wish to understand the role of the O antigen in resistance towards outer membrane disrupting antibiotics such as polymyxin B.