A31P NMR study of the interaction of amphibian antimicrobial peptides with the membranes of live bacteria

Amphibian skin is a rich source of peptides that are specific to pathogens and act by disrupting bacterial membranes. Three antimicrobial peptides were isolated from the skin glands of Australian tree frogs,Litoria caerulea andLitoria genimaculata. NMR spectroscopy was used to observe changes induced by these peptides in the31P resonances of bacterial membranes in vivo. Caerin 1.1 and maculatin 1.1, both wide-spectrum antibiotics disrupted the membranes ofBacillus cereus andStaphylococcus epidermidis (Gram-positive), leading to an increase in the isotropic31P NMR signal. Caerin 4.1, a narrow-spectrum antibiotic, however, did not affect the31P spectra of these organisms. The results demonstrate the use of31P NMR to study the effects of membrane-disrupting agents on the membranes of live bacteria.