View/Open - ARAN - National University of Ireland, Galway

Chapter 5
5.3.4. The density of biofilm formed over 168 hours using the microtitre
plate system
When S. enterica biofilm was developed over an extended period of time
(168 hours at 22°C), a similar pattern emerged in that the OD 590 readings
for replicate wells of the same strain indicated that there was a large
variation in repeated measurements. As displayed in Table 5.5, the mean
OD 590 and the standard deviation is underlined for 5 S. Agona strains due to
a small number of high OD 590 values for some observations for these strains.
The mean OD 590 of stained biofilm would be smaller if these outliers were
excluded. The full set of observations for all 13 strains is provided in
Appendix 2- Table 4.
When the mean density of biofilm formed by the strains was examined
after 168 hours incubation there was evidence to suggest that some strains
of S. Agona may form a more dense biofilm but overall this pattern was not
consistent for all strains after incubation at 22°C. This trend was also not
consistent for some strains when incubated at 37°C for the 168 hour
duration (Table 5.6) most likely due to high and low outliers in some of the
repeated reading of the OD 590 of S. Agona biofilm. The full set of
observations are provided in Appendix 2 – Table 5.
If the strains were to be grouped into the respective serovars as displayed
in Table 5.6, the S. Agona serovar has the largest mean OD 590 for all 3
serovars. As previously discussed, because of the variation in OD 590
readings within individual strains caution should be exercised when
grouping the strains together to compare the three S. enterica serovars.
Page 177