Capsular polysaccharides and lipopolysaccharides from two Bacteroides fragilis reference strains: chemical and immunochemical characterization

Abstract

Fermentor growth of Bacteroides fragilis under controlled conditions in a complex medium containing 1% glucose and 10% fetal calf serum resulted in high yields of bacteria. After hot phenol-water extraction of the organisms, capsular polysaccharide was isolated from the aqueous phase and purified by Sephacryl S-300 chromatography in a buffer with 3% sodium deoxycholate. Lipopolysaccharide was isolated by phenol-chloroform-light petroleum ether extraction. The capsular polysaccharide from B. fragilis strain NCTC 9343 contained six sugars: L-fucose, D-galactose, D- and L-quinovosamine, D-glucosamine, and galacturonic acid. The capsule of strain ATCC 23745 also contained D-glucose, L-fucosamine, L-rhamnosamine, and a 3-amino-3,6-dideoxyhexose but lacked D-quinovosamine. The latter capsule also contained alanine (4%). The capsular polysaccharides were different immunochemically by ELISA inhibition. The lipopolysaccharide of both strains contained the same sugars (L-rhamnose, D-glucose, D-galactose, and D-glucosamine) and fatty acids (13-methyl-tetradecanoic and 3-hydroxy-hexadecanoic and 3-hydroxy-15 methyl-hexadecanoic as major constituents) and were identical by ELISA inhibition.