Real-time attack on single Escherichia coli cells by the human antimicrobial peptide LL-37.
Sochacki. Kem A KA; Barns. Kenneth J KJ; Bucki. Robert R; Weisshaar. James C JC
Key Findings
- LL‑37 quickly saturates the outer membrane of E. coli (within 1 min) at low micromolar concentrations.
- Growth stops 5‑25 min later, likely because LL‑37 interferes with cell‑wall biogenesis, not because it immediately ruptures the inner membrane.
- Only after growth has halted does LL‑37 make the inner membrane permeable to GFP and Sytox Green, and dividing (septating) cells are attacked more readily than non‑dividing ones.
Practical Outcomes
- For biohackers, the work suggests that LL‑37’s antibacterial action is slower and depends on getting past the outer membrane first, so any DIY antimicrobial protocol would need to allow time for this translocation. It also hints that targeting bacterial cell‑wall synthesis may be a more reliable way to halt growth than trying to lyse cells outright, but the study does not provide human dosing or safety guidance.
Summary
The study shows that the human peptide LL‑37 sticks to the outer layer of E. coli within a minute, then moves inside and stops the bacteria from growing before it actually punches holes in the inner membrane. It seems to mess with the bacteria’s cell‑wall building process, especially in cells that are dividing.
Abstract
Natural antimicrobial peptides (AMPs) provide prototypes for the design of unconventional antimicrobial agents. Existing bulk assays measure AMP activity but do not provide details of the growth-halting mechanism. We use fluorescence microscopy to directly observe the attack of the human antimicrobial peptide LL-37 on single Escherichia coli cells in real time. Our findings strongly suggest that disruption of the cytoplasmic membrane is not the growth-halting mechanism. At 8 μM, LL-37 binding saturates the outer membrane (OM) within 1 min. Translocation across the OM and access to the periplasmic space (5-25 min later) correlates in time with the halting of growth. Septating cells are attacked more readily than nonseptating cells. The halting of growth may occur because of LL-37 interference with cell wall biogenesis. Only well after growth halts does the peptide permeabilize the cytoplasmic membrane to GFP and the small dye Sytox Green. The assay enables dissection of antimicrobial design criteria into two parts: translocation across the OM and the subsequent halting of growth.
Study Information
pubmed
2011
2011-04-04T00:00:00.000Z
10.1073/pnas.1101130108
259
28