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Chapter 2
also used “high” sonication conditions to remove Escherichia coli and P.
aeruginosa ATCC 27853 biofilm attached to a surface, however the exact
conditions used were not provided in the article describing the research
[114]. However, if high sonication conditions had been chosen without
assessment of cells recovery it may have been wrongly assumed that the
strains were unable to form a dense biofilm.
The complete removal of viable cells was confirmed with 12 of the 13
strains assessed using scanning electron microscopy. However the biofilm
formed by the LT2 strain was not fully removed using the same conditions
verified with all other 12 strains. This difference between the LT2 strain
and other S. Typhimurium strains is most likely attributable to the
described genetic variation of this strain with respect to sigma factor
(RpoS) [105]. This genetic difference may contribute to the strain being
more dense biofilm former than other strains tested (as seen in tables 2.5)
and in the formation of a more adherent biofilm. Due to this deviation of
biofilm removal the LT2 strain was excluded from statistical analysis.
The results demonstrate that there is a substantial range of intra-strain
variation between the biofilm cell density values achieved through
repeated measures (indicated in the respective tables through the use of
SD values). Variation between repeated experiments has also been
discussed elsewhere [117, 171, 183]. The variation of results is a widely
recognised limitation of the biological process with variables such as room
temperature, humidity and slight variation in manual procedures (such as
biofilm removal and enumeration) contributing to the variation in repeated
tests. The same level of variation has also been reported elsewhere using
the CBR method [72, 117, 124].
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