Critical aggregation concentrations of gram-negative bacterial lipopolysaccharides (LPS)

Bacterial endotoxins or lipopolysaccharides (LPS), cell wall components of gram negative bacteria, are involved in septic shock. While the carbohydrate structure of LPS have been studied in the past, little is known about the macromolecular structure and formation of LPS fragments in blood. It is believed that amphiphilic molecules such as LPS occur as monomers and aggregate into macromolecular structures above a critical micelle or critical aggregate concentration, CAC. The CAC of Lipid A, a LPS precursor, and several LPS serotypes of varying molecular weight and different polysaccharide chain lengths were established by static light scattering and by steady-state fluorescence spectroscopy by incorporation of the fluorescent probe, NPN, N-phenyl-1-naphthylamine. The CAC for short polysaccharide chain mutant LPS S.minnesota Re 595 (MW 2,500) and Lipid A from S.minnesota Re 595 (MW 2000) were 4 microM and 5 microM respectively. The CAC of LPS from heterogeneous long O-antigen polysaccharide chain bacterial serotypes: S.minnesota wildtype were 11 micrograms LPS/ml, S.typhimurium 14 micrograms LPS/ml and E.coli 0111:B4 22 micrograms LPS/ml, respectively. The results obtained suggests that critical aggregate concentration and solubility of LPS is a function of polysaccharide chain length.