Biomedical Engineering Reference
In-Depth Information
details. Although higher resolution is usually obtained in air, bacteria imaged in liquid are
closer to the native state, and dried bacteria usually have a small fraction of their hydrated
height [6, 315, 621].
One of the most important areas in studies of bacteria is the study of the method of
action of antibiotics and other antibacterial agents, due to the ongoing increase in antibi-
otic resistance in bacteria [627]. Several studies have imaged bacteria treated with anti-
microbial agents, including the morphological changes to
E. coli
caused by the antibiotic
cefodizime [628] and also
E. coli
and
P. aeruginosa
response to antibacterial peptides
[629, 630],
S. aureus
response to antibiotics [631, 632] and others [624, 633, 634]. The
response to the natural antimicrobial polymer chitosan, of
E. coli, S. aureus
,
B. cereus
and
B. cereus
spores has been measured by both AFM imaging and nanoindentation measure-
ments [169, 178]. The changes that can be seen include morphological alterations such as
appearance of holes, shrinking, cell shape changes and cell lysis, and also mechanical
changes. An example showing the response of
S. aureus
to antibiotic treatment by both
topographic changes and changes in cell elasticity is shown in Figure 7.21.
20 minutes
40 minutes
80 minutes
100 nm
20
No treatment
80 minutes treatment
15
10
5
0
0
1000
2000
0
1000
2000
Young's Modulus (kPa)
Fig. 7.21. An example of the use of AFM to measure bacterial response to antibiotic treatment. Top:
topographical images showing cell wall roughening in
S. aureus
after increasing times of treatment
by the antibiotic lysostaphin. The images are deflection images measured in contact mode. Below:
the effect on cell wall stiffness. The drug appears to severely degrade the cell wall within 80 minutes.
This data was collected in buffer solution, on a cell trapped in a membrane pore. Reproduced with
permission from [632].
