Interactions between the antimicrobial peptide, magainin 2, and Salmonella typhimurium lipopolysaccharides.

Using FT-IR spectroscopy, the effects of magainin 2 on the thermotropic behavior of LPS isolated from wild-type (SL3770) and LPS-mutant strains of Salmonella typhimurium are characterized and compared. The mutant strains include Ra (SL3749), polymyxin-sensitive Rb2(s) (SH5014), polymyxin-resistant Rb2(r) (SH5357) and Rc (HN202) LPS chemotypes, whose polysaccharide chains differ in length but possess an identical number of phosphorylation sites. In all cases, magainin 2 causes a concentration-dependent disordering of the LPS fatty acyl chains. Differences in disordering of LPS correlate more closely with the charge on the LPS molecule (determined by high-resolution 31P NMR) rather than with the length of the LPS sugar side chain, contradicting the currently accepted model for the interaction of cationic antibiotics with the Gram-negative cell envelope.