Detection of submicrogram quantities of Escherichia coli lipopolysaccharides by agarose-gel electrophoresis

A sensitive agarose-gel electrophoresis method has been developed for the visualization of lipopolysaccharide (LPS) samples from several Escherichia coli serotypes, such as 026:136, 055:135, 0128:1312, 0111:134, 0127:138, and K235. This method can detect as little as 0.5-6 mug of LPS depending on the serotype by treatment of the plates with toluidine blue, and it is able to measure submicrogram amounts of samples, approx. 0.05-0.5 mug, when the staining with toluidine blue followed by Stains-All procedure is adopted. Treatment of LPS with alkali under anhydrous conditions removes the ester-linked fatty acids and the phosphate groups of the Lipid A component, producing the detoxified LPS. The carbohydrate neutral moiety obtained from the hydrolysate does not migrate during electrophoresis. This was utilized to monitor quantitatively the removal process of the Lipid A component for the formation of the detoxified LPS.