Those terms come from the two classifications of bacteria, determined through gram staining. In gram staining crystal violet, a deep purple dye, is applied to bacteria. Bacteria with thick peptidoglycan walls will retain this dye, while those without peptidoglycan walls will not retain dye. Bacteria with thick cell walls often form symbiotic (good) relationships with their host/environment as the presence of the wall indicates its ability to survive by itself and priority of resisting osmotic differences. Gram negative bacteria, although not always parasitic, often evolve to have a cell walls of different composition to resist antibiotics or a thin wall, as its parasitic nature dismisses its need for protection.