Biomedical Engineering Reference
In-Depth Information
Fig. 7.20. Studies of bacterial morphology. Top left:
Streptococcus
, showing typical linear clusters.
Top right: large clusters of
Staphylococcus aureus
. Bottom left:
Salmonella
biofilm showing pili-like
fimbrial structures. Bottom right:
E. coli
. All these images were measured in air. Reproduced with
permission from [624] (top left) and [626] (bottom left).
needs to be careful of drying artefacts by these techniques [621]. However, it is useful to
be able to study bacteria in liquid, and usually this requires a more elaborate preparation
protocol because it's necessary that the cells be fixed to the substrate in some way. The
most commonly used techniques include the use of poly-l-lysine (PLL) or polyethylenei-
mine (PEI) coating of glass for chemical capture and using gelatin-coated glass for a soft
physical capture [6, 314, 315]. For spherical bacteria, i.e. cocci, physical trapping of
substrates with appropriately-sized holes works well, and it can even be possible to
observe the cells dividing while immobilized in this way [313, 317]. Bacteria that
naturally form biofilms are simple to study as biofilms are perfect samples for AFM,
although some washing may be required. See Section 4.1 for more sample preparation
