 There are two main types of bacteria and they are Gram-negative and Gram-positive.The two bacteria types differ in the composition of their membrane.The Gram-negative bacteria have an outer lipopolysaccharide membrane and a thin peptidoglycan layer followed by a phospholipids bilayer, whereas the Gram-positive bacteria lack the outer membrane and carry a thicker peptidoglycan layer as well as a phospholipids bilayer.