Ultrastructure of lipopolysaccharides of Yersinia enterocolitica, Salmonella typhimurium and Escherichia coli.

The fine structure of isolated lipopolysaccharides (LPS) from the rough and smooth form of an Yersinia enterocolitica strain (Ye 75 R/Ye 75 S) and from smooth forms of Salmonella typhimurium (S 1010) and Escherichia coli (Essen) were examined electron-microscopically by negative staining. Partial denaturation of LPS in Tris-buffer with acid and/or polymyxin B treatment revealed a common structure of strandlike LPS. Electron-microscopically, LPS-strands were found to consist of two identical sub-strands which form a double helix. High resolution electron microscopy permitted the identification of a total of four longitudinal fibrils (diameter approximately 20 A); therefore, each sub-strand consists of two longitudinal fibrils. These results were correlated with those obtained with positive staining procedure and chemical fixation technique. The development of the "double-track"-profile of the outer membrane was interpreted to result from the projection of the helical longitudinal fibrils into the image plane.