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Chapter 5
measures of S. enterica biofilm formation [56, 96]. However, the use of
standard errors to demonstrate variance between repeated measures in
the absence of standard deviations or confidence intervals is not
recommended [233-234].
Previous published material in this area by Lianou et al. has also reported
large variation in S. enterica biofilm density using the microtitre plate
method stained with crystal violet [191]. Lianou et al. reported large
variation on mean OD 590 measurements and standard deviations of S.
enterica serovars similar to that reported here. However, the author does
not indicate if inter-run variation (repeatability) may have been responsible
for some of this variation or if the variation was more related to differences
between the strains in each categorised serovar. Moreover, the author
stresses the need for inclusion of multiple strains of S. enterica serovars in
any comparisons of serovars to ensure that the data is an accurate
representation of the variation in biofilm density [191].
Taking into consideration the variation in repeated measures, there is still
evidence to suggest S. Agona strains may form a more dense biofilm than
S. Typhimurium and S. Enteritidis strains, particularly after 48 hours
incubation at 22°C (section 5.3.3). Similarly, Vestby et al. also found S.
Agona and S. Montevideo formed a more dense biofilm than other
serovars (S. Typhimurium and S. Senftenberg) using the microtitre plate
method [56]. Although as previously discussed, the authors used the
median measurements standard error to report the variation in the 3
repeated measures for each strain examined [56]. As a result, it is difficult
to compare the results presented in this chapter to what was reported by
Vestby et al. using the same method. However, the standard error from
this work (data not shown) is similar to that reported by Vestby et al. which
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