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Published on: July 25, 2012
Atomic Force Microscopy Reveals the Mechanobiology of Lytic Peptide Action on Bacteria
Anna Mularski1, Jonathan J Wilksch1, Huabin Wang1
1†School of Chemistry, ‡Department of Microbiology and Immunology, The Peter Doherty Institute for Infection and Immunity, and §Florey Institute for Neuroscience and Mental Health, The University of Melbourne, Melbourne, VIC 3010, Australia.
Abstract:
Increasing rates of antimicrobial-resistant medically important bacteria require the development of new, effective therapeutics, of which antimicrobial peptides (AMPs) are among the promising candidates. Many AMPs are membrane-active, but their mode of action in killing bacteria or in inhibiting their growth remains elusive. This study used atomic force microscopy (AFM) to probe the mechanobiology of a model AMP (a derivative of melittin) on living Klebsiella pneumoniae bacterial cells. We performed in situ biophysical measurements to understand how the melittin peptide modulates various biophysical behaviors of individual bacteria, including the turgor pressure, cell wall elasticity, and bacterial capsule thickness and organization. Exposure of K. pneumoniae to the peptide had a significant effect on the turgor pressure and Young's modulus of the cell wall. The turgor pressure increased upon peptide addition followed by a later decrease, suggesting that cell lysis occurred and pressure was lost through destruction of the cell envelope. The Young's modulus also increased, indicating that interaction with the peptide increased the rigidity of the cell wall. The bacterial capsule did not prevent cell lysis by the peptide, and surprisingly, the capsule appeared unaffected by exposure to the peptide, as capsule thickness and inferred organization were within the control limits, determined by mechanical measurements. These data show that AFM measurements may provide valuable insights into the physical events that precede bacterial lysis by AMPs.
Insights
Antimicrobial peptides (AMPs) show promise for treating resistant bacteria. This study used atomic force microscopy to reveal how a model AMP affects bacterial cell mechanics, leading to lysis.
Area of Science:
- Microbiology
- Biophysics
- Biochemistry
Background:
- Rising antimicrobial resistance necessitates novel therapeutics.
- Antimicrobial peptides (AMPs) are potential candidates, but their mechanism of action is unclear.
- Many AMPs target bacterial membranes, but their precise effects on cell biophysics are not fully understood.
Purpose of the Study:
- To investigate the mechanobiology of a model antimicrobial peptide (AMP) on living Klebsiella pneumoniae cells.
- To elucidate how AMPs modulate bacterial turgor pressure, cell wall elasticity, and capsule properties.
- To understand the physical events preceding bacterial lysis induced by AMPs.
Main Methods:
- Utilized atomic force microscopy (AFM) for in situ biophysical measurements on individual Klebsiella pneumoniae cells.
- Measured changes in turgor pressure and cell wall elasticity (Young's modulus) upon AMP exposure.
- Assessed bacterial capsule thickness and organization through mechanical property analysis.
Main Results:
- Exposure to the model AMP significantly altered K. pneumoniae turgor pressure, initially increasing then decreasing, indicating cell lysis.
- The peptide increased the Young's modulus of the cell wall, suggesting enhanced rigidity.
- The bacterial capsule did not impede AMP-induced lysis and remained mechanically unaffected.
Conclusions:
- AFM provides valuable insights into the physical mechanisms of bacterial lysis by AMPs.
- AMPs can disrupt bacterial cell integrity through mechanical modulation of the cell envelope.
- The bacterial capsule does not confer resistance to AMP-mediated lysis in K. pneumoniae.
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