MICROBIAL CELL IMAGING USING ATOMIC FORCE MICROSCOPY - Life at the Nanoscale: Atomic Force Microscopy of Live Cells - page 52

(a) (b) (c) (d)

(e) (f) (g) (h)

Figure 3.2. Mid-exponential P. aeruginosa ( PA14) cells treated with 10 μg/ml colistin
for 3 hours and imaged in 0.25 M sucrose. (a-b, e-f ) are MACmode images while
(c-d, g-h) are contact mode images. In the untreated controls, (a) topography and (b)
amplitude are Macmode images, while (c) topography and (d) delection are contact
mode images. Cells treated with colistin and imaged in MACmode are shown in (e)
and (f ), while contact mode images are shown in (g) and (h). The surface structures in
MACmode appear “spiky,” while contact mode images appear wavy.

(a) (b)

Figure 3.3. Immobilized E. coli spheroplasts imaged in liquid in contact and non-
contact modes. (a) Contact mode imaging imposes the shape of the probe into the
image as it contacts the pliable spheroplasts. (b) Non-contact mode (MACmode)
imaging causes less disturbance of the cell shape.

Other imaging artifacts can result from the shape of the probe tip and
the forces exerted by it as irst described by Velegol . 47 The relatively tall

microbial cell requires slow scanning speeds and careful optimization of gain
settings to enable the tip to track over the cell without signiicantly disturbing
it. Further, in the early AFM studies of bacteria in liquid, it was speculated that
material was being scraped off the cell surface resulting in the piling up of

et al