Biology Reference
In-Depth Information
In one study, the microbial response to differences in growth conditions
shows that the organization of
S-layer is
dependent on the growth media. This work showed that AFM images of
C. glutamicum
Corynebacterium glutamicum
grown in nutrient-rich media had a smooth surface with no
ordered S-layer visible, while bacteria grown in brain-heart infusion media
showed a highly ordered hexagonal lattice S-layer.
60
An early AFM-based
study in air examined the response of
to different concentrations
of ethylenediaminetetraacetic acid (EDTA). AFM images of dried samples
revealed changes in bacterial surface morphology and collapsed cells due
to the EDTA treatment. The study also showed that metal depletion caused
irregularly shaped pits in the cell's outer membrane.
11
AFM has also been
used to visualize morphological changes in
E. coli
after bacteriophage
infection. AFM images taken in air showed increased smoothness and
decreased bacterial height.
E. coli
61
Several reports have established the utility of AFM in understanding
the mechanism of antibiotic action. AFM has been used to examine the
mechanism of action for a range of antimicrobial peptides including PGLa,
62,63
magainin 2, melittin,
63
SB006
64
and the so-called sushi peptides.
65
In all cases,
AFM images in air show that the antimicrobial peptides caused damage to the
bacterial cell envelope. AFM has also been used to study in air the effects of
exposure of various bacteria to the antibiotic cefodizime,
a polymeric drug
risug,
66
nanoparticles bound to lysozyme
67
and nitric oxide (NO).
68
In both
cefodizime- and risug-treated
8
, the centre of the cells was observed
to be collapsed when imaged in air, and a knobby and irregular appearance
to the bacterial surface was also seen. Silver nanoparticles coupled with
lysozyme showed strong antimicrobial properties on
E. coli
Proteus mirabilis
and
E.
coli
where AFM imaging in air revealed a partially destroyed cell envelope.
67
E. coli and
exposed to NO showed morphology similar to
bacteria exposed to the antibiotic amoxicillin, indicating that NO leads to cell
envelope deterioration.
68
AFM revealed that bacitracin, a metal-dependent
dodecapeptide, inhibited cell growth and division in
P. aeruginosa
Staphylococcus aureus
and that the effect of bacitracin was increased when the peptide was coupled
to metal ions.
69
The antimicrobial effect of chitosan was investigated on both
vegetative bacteria and its spores of
. AFM showed that the
polymer forms a ilm that surrounds the cells.
13
A study of the antimicrobial
peptide colistin performed on living
Bacillus cereus
in liquid showed that the
cell morphology changed to a wavy phenotype and increased stiffness of the
cell surface.
30
As a natural extension to studying single cells, bacterial communities
such as bioilms have also been investigated.
57,70
AFM has been used to study
bioilm organization, response to chemical exposure and bacterial predation.
Most studies have examined the early stages of bioilm formation and are
carried out in air. Hydrated, mature bioilms have dramatic topographies and
P. aeruginosa
Search WWH ::
Custom Search