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Chapter 2
2.7. Discussion
The results of the quality control experiments suggest that caution is
needed when using sonication for biofilm removal. As reported elsewhere
researchers should examine the surfaces or biofilm substrata post removal
to verify complete removal and confirm validity of the removal method
[183]. The results of the quality control experiments indicate that swabbing
the surface with a pre-moistened sterile swab was not an effective method
for removing all biofilm cells from the entire surface (Table 2.2). Figure 2.4
also illustrates biofilm cells remained on both the smooth (glass) and
porous/rough surface (concrete) after swabbing. Moreover cotton deposits
remained on the surface after contact with the surface. If this method is
chosen in experiments such as those described by Joseph et al. [71], it may
result in an underestimation of the biofilm density on a test surface. The
research published by Joesph et al. did not indicate if SEM or any
microscopy was performed in order to validate the swabbing method for
biofilm removal. Incomplete removal post swabbing may have contributed
to the finding of a more dense biofilm recovered from plastic than concrete
(cement) [71] which is the opposite to what was found in the research
reported in this thesis.
The quality control results also indicated that sonication at 20 kHz was the
most appropriate sonication condition for removal of S. enterica cells
without reducing the number of viable cells. Based on the results
presented in this chapter, quality control measures should be performed to
ensure cells are not damaged by sonication. Curtin et al. used the same
model sonication bath previously at 45-49 kHz for 30 minutes to remove S.
epidermidis biofilm cells from catheter associated surfaces [186]. It is
possible that the high sonication conditions may be suitable for gram
positive organisms such as S. epidermidis. However previous authors have
also used higher sonication such as 27 kHz [118] or 42 kHz [72] over short
intervals to remove biofilm consisting of gram negative organisms such as P.
aeruginosa, Klebsiella pneumoniae and Shewanella putrefaciens. Ceri et al.
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