Atomic Force Microscopy Reveals the Mechanobiology
of Lytic Peptide Action on Bacteria
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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 <i>Klebsiella pneumoniae</i> bacterial cells.
We performed <i>in situ</i> 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 <i>K. pneumoniae</i> 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