In vitro susceptibility tests for cationic peptides: Comparison of broth microdilution methods for bacteria that grow aerobically

The in vitro susceptibilities of 90 clinical isolates of gram-positive and gram-negative aerobic bacteria to six cationic peptides, buforin II, cecrop in P1, indolicidin, magainin II, nisin, and ranalexin, were evaluated by tw o broth microdilution methods. The first method was performed according to the procedures outlined by the National Committee for Clinical Laboratory S tandards for bacteria that grow aerobically, while the second was performed according to the procedures recently proposed by the R. E. W. Hancock labo ratory for testing antimicrobial peptides. Overall, the first method produc ed MICs two- and fourfold higher than the second method.