CHARACTERIZATION OF LIPOPOLYSACCHARIDES OF POLYMYXIN-RESISTANT AND POLYMYXIN-SENSITIVE KLEBSIELLA-PNEUMONIAE-03

Lipopolysaccharides isolated from the polymyxin-resistant Klebsiella p neumoniae O3 mutant OM-5 and its polymyxin-sensitive parent LEN-1 were analyzed for chemical composition, and their lipid A portions were st ructurally characterized. The lipopolysaccharide of OM-5 contained app roximately five times more 4-amino-4-deoxy-L-arabinopyranose than that of LEN-1. Other saccharide and phosphate components exhibited no sign ificant differences. Structural characterization, including analyses b y phosphorus magnetic resonance spectroscopy and by fast atom bombardm ent mass spectrometry, revealed a novel type of lipid A. In the OM-5 l ipopolysaccharide, both phosphates of lipid A were almost totally pres ent as phosphodiesters with 4-amino-4-deoxy-L-arabinopyranose. In the sensitive-type LEN-1 lipid A, the extent of this substitution was much lower, especially in the glycosidically linked phosphate. Phosphate i n these K. pneumoniae lipopolysaccharides was almost exclusively found in lipid A. These results show that cationic substituents of phosphat es of lipid A play a decisive role in determining polymyxin reactivity . OM-5 was also found to contain a large proportion of heptaacyl lipid A, which represented only a small fraction of lipid A in LEN-1.