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Chapter 6
6.8. Limitations of the Studies
6.8.1. Incomplete removal of biofilm cells from the surface
Scanning electron microscopy was used for all experiments performed
using the CBR to assess completeness of biofilm removal from the surfaces
by sonication. Based on the evaluation of all 13 strains investigated for
biofilm formation over 48 hours, only one strain (S. Typhimurium LT2) was
not fully removed using the conditions described in. This finding highlights
the need to use SEM or other forms of microscopy to confirm removal of
biofilm from a surface which is used for enumeration and comparative
purposes as conclusions based on inconsistent removal are more difficult
to interpret.
6.8.2. Incomplete removal of the mature biofilm
As discussed in chapter 3, sonication under the conditions described was
used to maximise removal of biofilm from the surfaces post developed
over 168 hours. The results of chapter 2 and 3 indicate that sonication
removed more biofilm from the surface than swabbing the surface but that
increasing the sonication power or duration was not as effective as it
impacted on cell viability. As a result, incomplete removal decreases the
validity of using a plate count method to determine the density of 168 hour
biofilm attached to the surface. If viable counts are to be applied to assess
density of such biofilm then development of acceptable methods to
achieve full removal without impairment of cell viability are necessary. An
alternative is to work on developing methods that achieve enumeration of
viable cells without biofilm detachment such as the use fluorescent
staining, which also has certain limitations as discussed in chapter 2.
Due to incomplete removal of the 168 hour biofilm, direct comparisons
(biofilm log 10 density levels after 48 and 168 hours) should be looked at
with a degree of caution. Incomplete but variable removal may be
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