CHARACTERIZATION OF THE EXTERNAL SURFACES OF PSEUDOMONAS-AERUGINOSA ISOLATED FROM HUMAN BLOOD AND RESPIRATORY-TRACT

The surface structures of the cell envelopes of 16 clinical isolates o f Pseudomonas aeruginosa were examined by electronmicroscopy with the new fixation technique of freeze-substitution. Two types of structures were observed among the organisms. In one group of strains, mostly is olated from blood, a dense fibrous layer c. 30 nm thick was found arou nd the outer-membrane surface, whereas no such structure was observed in the other group of isolates, most of which were from sputum. Lipopo lysaccharides extracted from the isolates with a dense fibrous layer w ere found by SDS-PAGE to have long O-polysaccharide chains, whereas st rains without such a layer mostly had lipopolysaccharides that lacked high mol, wt. O-polysaccharide chains.