ANTIMICROBIAL ACTIVITY OF CECROPINS

The lytic peptides, cecropins, were originally isolated from the haemo lymph of the giant silk moth, Hyalophora cecropia and possess antibact erial and anticancer activity in vitro. This study investigated the an timicrobial activity of these peptides against human pathogens using s tandardised assay techniques, and the activity of cecropin B on outer and inner bacterial membranes. From a panel of 15 organisms, Gram-nega tive bacteria were generally more sensitive to cecropins than Gram-pos itive organisms, especially the lipopolysaccharide defective mutant, E scherichia coli BUE55. Cecropins B and P-1 shared similar MIC values w hereas Shiva-l, a cecropin B analogue, was less active. Through combin ation studies with hydrophobic antibiotics and electron microscopy, ce cropin B was shown to disrupt the bacterial outer membrane. Protoplast s of Staphylococcus aureus and Staphylococcus epidermidis were resista nt to cecropin B, suggesting that the cytoplasmic membranes of Gram-po sitive organisms were inherently more resistant to the peptide.