In vitro antimicrobial activity of MSI-78, a magainin analog

MSI-78 is a cationic peptide with broad-spectrum antimicrobial activity and is being developed as a topical agent. We compared the in vitro activity of MSI-78 with those of ofloxacin and other antibiotics against fresh clinical isolates. Based on MIC distribution statistics, strains for which the MSI-78 MIC was less than or equal to 64 mu g/ml were assumed to be susceptible for purposes of this report. Of 411 aerobic isolates tested, 91% were susceptible to MSI-78, compared to 91% for ofloxacin and 92% for ciprofloxacin. Only enterococci consistently required greater than or equal to 64 mu g of MSI-78/ml for inhibition. MSI-78 demonstrated bactericidal activity equivalent to that of ofloxacin, Of 61 anaerobes, 97% were susceptible to MSI-78, Of 10 isolates of Candida albicans, 3 were inhibited by MSI-78 at 24 h, Further studies of this compound appear to be warranted.