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Chapter 6
to emphasise the importance of choosing multiple strains when designing
experiments of this nature.
6.4. Biofilm formation using the microtitre plate method
It is important to note that any comparison made based on the mean OD 590
data presented in chapter 5 are made with caution due to the substantial
range of the 9 OD 590 measurements for single strain. The large variation in
repeated measures was much greater than that observed using the CBR (as
indicated through standard deviations in each chapter). Variability may
reflect uneven biofilm formation (and subsequent failure to resuspension
in ethanol: acetone) by S. enterica in the microtitre plate method as
suggested elsewhere [178]. However, it is also possible that some
adaptation of the biofilm development method or evaluation of biofilm
density may have resulted in greater repeatability however time
constraints did not permit further optimisation of the method.
Nevertheless, tentative suggestions of overall trends are made here based
on those results. To describe the full extent of variation, the full set of
OD 590 measurements are provided in Appendix 2.
Overall, most of the S. Agona strains were more dense biofilm formers
after 48 hours in comparison to most of the S. Typhimurium and S.
Enteritidis strains. However, this trend was not consistent throughout,
possibly due to the variation of OD 590 of repeated measurements.
Interestingly, when the biofilm was established at 22°C only 4 of the 13
strains had a higher mean OD 590 after 168 hours. There was no difference
or only a marginal difference in the density of biofilm after extending the
period of time to 168 hours (~0.1-0.2 mean OD 590 ). Two strains, S. Agona
strains S08-0601 and S. Typhimurium SL1344 showed a larger difference in
terms of mean OD 590 over time. However the difference observed was
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