In vitro activity and potency of an intravenously injected antimicrobial peptide and its DL amino acid analog in mice infected with bacteria

Abstract

We report that intravenous injection (3 mg/kg of body weight twice daily) of a diastereomer (containing 33% D amino acids) of an antimicrobial peptide, K6L9 (LKLLKKLLKKLLKLL-NH2), but not the all-L-amino-acid parental peptide, cures neutropenic mice infected with gentamicin-sensitive Pseudomonas aeruginosa and gentamicin-resistant Acinetobacter baumannii bacteria. Various biophysical experiments suggest a membranolytic-like effect.

FIG. 1.

(A) In vitro time-kill curve of amphipathic-d at its MIC; (B and C) membrane depolarization in bacteria (filled triangles) and bacterial spheroplasts (filled circles) of gentamicin-resistant A. baumannii induced by amphipathic-d as a function of the peptide concentration (B) and time (C). The diastereomer at its MIC was added to bacteria or spheroplasts that had been preequilibrated with the fluorescent dye diS-C₃-5 for 60 min. Fluorescence recovery was measured 1 to 120 min (at 5-min intervals) after the diastereomer was mixed with the bacteria, and its maximum was recorded. The arrows in panel B indicate the peptide's MICs.

FIG. 2.

Mortality of infected mice after systemic treatment with phosphate-buffered saline (black bars), amphipathic-l (gray bars), amphipathic-d (empty bars), and gentamicin (dotted [rightmost] bars). Mortality was monitored for at least 10 days posttreatment.