Abstract
The surface structures of the cell envelopes of 16 clinical isolates of 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 isolated from blood, a dense fibrous layer c. 30 nm thick was found around the outer-membrane surface, whereas no such structure was observed in the other group of isolates, most of which were from sputum. Lipopolysaccharides extracted from the isolates with a dense fibrous layer were found by SDS-PAGE to have long O-polysaccharide chains, whereas strains without such a layer mostly had lipopolysaccharides that lacked high mol. wt. O-polysaccharide chains.