Evaluation of Some Extraction Methods for the Preparation of Bacterial Lipopolysaccharides for Structural Analysis

The extraction of lipopolysaccharides (LPS) from smooth strains of Salmonella typhimurium for structural studies using methylation analysis is preferably done by hot phenol‐water method on a cell‐wall preparation obtained by mechanical disintegration of γ‐irradiated bacteria. The LPS obtained by this method was less contaminated than LPS extracted by hot phenol‐water from acetone dried bacteria or bacteria pretreated with 1 per cent formaldehyde. LPS for structural analysis from rough mutants is, due to its lipophilic character, preferably extracted with a mixture of phenol, chloroform and petroleum ether. The presence of the precursor of the O side‐chain, LI‐hapten, in the different LPS‐ and supernatant fractions was assessed by gel precipitation tests. The LPS forms a line near the antigen well whereas the low molecular weight hapten forms a line near the antiserum well. The hapten was not formed in excess in the smooth strain S. typhimurium LT2. In the rough mutant studied, S. typhimurium SL 733, O‐antigenic material was found in both the LPS‐preparation (probably as a covalently linked O side‐chain) and the supernatant (as a hapten).