Antimicrobial protein rBPI21-induced surface changes on Gram-negative and Gram-positive bacteria

New classes of antibiotics, such as antimicrobial peptides or proteins (AMPs), are crucial to deal with threatening bacterial diseases. rBPI(21) is an AMP based on the human neutrophil BPI protein, with potential clinical use against meningitis. We studied the membrane perturbations promoted by rBPI(21) on Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. Its interaction with bacteria was also studied in the presence of lipopolysaccharide (LPS), rBPI(21) major ligand. Flow cytometry analysis of both bacteria shows that rBPI(21) induces membrane depolarization. rBPI(21) increases the negative surface charge of both bacteria toward positive values, as shown by zeta-potential measurements. This is followed by surface perturbations, culminating in cell lysis, as visualized by atomic force microscopy (AFM). Force spectroscopy measurements show that soluble LPS decreases the interaction of rBPI(21) with bacteria, especially with S. aureus. This suggests that the rBPI(21) LPS-binding pocket may also participate on the binding to Gram-positive bacteria. From the Clinical Editor: In this study, rBPI(21), an antimicrobial protein based on the human neutrophil BPI protein, with potential clinical use against meningitis, is analyzed with multiple tools including zeta-potential measurements, clarifying its actions on E. coli and S. aureus. Since antimicrobial peptides are potentially important new additions to antibiotic regimens, studies like this represent important cornerstones in efficiency and mechanism of action testing of these new approaches. (C) 2014 Elsevier Inc. All rights reserved.