FIG. 1.

Effects of two LAH antibiotic peptides and magainin 2 on culture OD₆₀₀ at both acidic and neutral pHs. The peptides were added at concentrations corresponding to their MIC₅₀s, MIC₁₀₀s, and two times the MIC₁₀₀s. The optical densities of the test bacteria are shown after 10 min (T₀) and 2 h (T₁) of incubation for LAH6-L1 against B. megaterium (A) and LAH4 (B) and magainin 2 (C) against E. coli. The error bars represent the standard deviations of the mean, while an asterisk denotes a P value of <0.01 for T₁ measurement compared with both control and T₀ measurements. Bacterial (E. coli) viability after incubation with peptide under the same conditions is shown by the number of colonies produced on a solid support (D). LAH4-L1 and LAH6-L1 were effective bactericidal peptides despite the apparent lack of membrane disruption, but a large number of cells remained viable after treatment with LAH4-L1-F1 at neutral pH. More than 3,000 colonies were counted on plates with no peptide treatment.