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Chapter 6
previously published material has published on 3 replicate wells from one
experiment or have not provided the figures to examine the extent of
variation in tabular format (graphs only) [56, 178].
6.8.4. Reasons for variation using the microtitre plate bases system
As discussed in the limitations of the research performed in chapter 5,
there may be a number of reasons for this variation in SD values. First, it
was evident from repeated examination that the optical density reader
may not provide consistent values even on repeated examination of the
same microtitre plate (see Table 5.1 in chapter 5 and Table 1 in Appendix 2
for details). It is also possible that slight variation in the position held in the
automated reader may result in a different area going under examination.
Low speed shaking of the inoculated microtitre plates during incubation
may alleviate some aggregation of biofilm cells, however the aggregation
may also represent the heterogeneous formation of macro-colonies on the
surface. Moreover, post staining with crystal violet, it was apparent that
the crystal violet stain was not completely eluted from the biofilm
uniformly across the entire surface of the plate. It is possible that the use
of other reagents such as glacial acetic acid [111-112, 135, 165] instead of
ethanol: acetone may have been more effective. Others have achieved
greater repeatability using this method [111-112, 165]. Due to time
constraints this method could not optimized for the research presented in
chapter 5.
6.8.5. The limitations of using repeated measurements
Although the level of repeatability presented in this work, broadly
corresponds to what has been reported elsewhere, there is still a need to
exercise caution when interpreting results. Due to the small sample size (6-
9 observation in most comparisons of individual strains), the findings may
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